Laparoscopic Imaging Systems
It is well known that laparoscopy is the consequence of advances made in the field of medical engineering. Each surgical specialty has different requirements for instruments. Laparoscopy was initially criticized owing to the cost of specialized instruments and possible complications due to these sharp long instruments. Also, it necessitated difficult hand-eye coordination. Gradually, the technique gained recognition and respect from the medical fraternity since it drastically reduced many of the complications of the open procedure.
Minimal access surgery has developed rapidly only after the grand success of laparoscopic cholecystectomy. Computer-aided designing of laparoscopic instruments is an important branch of medical engineering. It is now possible to control access through microprocessor controlled laparoscopic instruments. New procedures and instruments are innovated regularly which makes it important for the surgeon to be familiar with the developments. Laparoscopy is a technologically dependent surgery and it is expected every surgeon should have reasonably good knowledge of these instruments.
LAPAROSCOPIC TROLLEY
The mobile laparoscopic video cart is equipped with locking brakes and has four anti-static rollers. The trolley has a drawer and three shelves. The upper shelves have a tilt adjustment and used for supporting the video monitor unit. Included on the trolley is an electrical supply terminal strip, mounted on the rear of the second shelf (from the top). Recently, ceiling-mounted trolleys are launched by many companies that are ergonomically better and consume less space in the operation theater.
IMAGING SYSTEMS
• Light source
• Light cable
• Telescope
• Laparoscopic camera
• Laparoscopic video monitor
The imaging system is a chain of equipment that are link together in place perfectly and functioning well to produce an excellent laparoscopic image. The break-in this sequential pass of links of the chain will be rendered our imaging system impotent.
The classic imaging chain starts with a light source, and ends in the monitor, requiring seven pieces of equipment, known as the Magnificent Seven: light source, fiberoptic light cable, laparoscope, camera head, video signal processor, video cable, and monitor. This imaging chain is often supported by a cast of VCRs, photo printers, or digital capture devices. The surgeon and the operating room team must work together to ensure optimal equipment function through careful handling of the equipment in the operating room and during the sterilization process. Yet, when the image is poor, many operating teams become paralyzed, unable to function without the aid of a medical engineer. “Understanding can overcome any situation, however, mysterious or insurmountable, it may appear to be.” Accordingly, understanding the (imaging) video system will allow the operating surgeon to do the basic troubleshooting for his or her system and not be totally dependent on nursing or technical staff, especially at night when experienced personnel may not be available. The advent of integrated operating suites has not changed the principles of this basic idea.
LIGHT SOURCE
It is clear and easy to say that, life, recently, is impossible without light, and simply: no light, no laparoscopy. The light source is the often-overlooked soldier of the video laparoscopic system.
A high-intensity light is created with bulbs of halogen gas, xenon gas, or mercury vapor. The bulbs are available in different wattages “150 and 300 Watt” and should be chosen based on the type of procedure being performed. Because light is absorbed by the blood, any procedure in which bleeding is encountered may require more light. We use stronger light sources for all advanced laparoscopy. The availability of light is a challenge in many bariatric procedures where the abdominal cavity is large.
A good laparoscopic light source should emit light as much as possible near the natural sunlight.
Three types of the light source are in use today:
1. Halogen light source
2. Xenon light source
3. Metal halide light source
The output from the light sources is conducted to the telescope by light cables that contain either glass fiber bundles or special fluid. The halogen light source is used in the medical field for the last 20 years, but the spectral temperature of these lights is 3200 Kelvin which makes it too different and too low from natural sunlight. The midday sunlight has approximately 5600 Kelvin color temperature. In practice, the yellow light of the halogen bulb is compensated for in the video camera system by white balancing.
A more suitable light source for laparoscopic cameras involves the creation of an electrical arc in a metal halide system or in xenon. This electrical arc is produced in the same way as in a flash of the photographic camera. Xenon has a more natural color spectrum and a smaller spot size than halogen. The xenon light source emits a spectral temperature of the color of approximately 6000 Kelvin on average for a power of 300 W
Arc generated lamps have a spectral temperature that gradually decreases with use and white balance is required before each use. The bulb needs replacing after 250 to 500 hours of usage, depending on the type of lamp. One of the main advantages of the laparoscopy is that of obtaining a virtually microsurgical view compared to that obtained by laparotomy. The quality of the image obtained very much depends on the quantity of light available at each step of the optical and electronic system.
The Interface of the laparoscopic teamwork with a Standard Light Source:
It is essential for the laparoscopic team, particularly the surgeons, to know about all the switch and function of the light source. All essential details of the equipment and all the action required on the part can be found on the operating manual of the product.
Many light sources record and display the hours of service and alert the biomedical medical engineer (or the well- informed surgeon) when it is time to make a change. When the lifetime rating of the bulb has been exceeded, the subsequent performance of the light source becomes unpredictable, often slowly dwindling until the surgeon just can not produce a well-lit scene despite the fact that bright light seems to emanate from the laparoscope.
A typical light source consists of:
• A lamp (bulb)
• A heat filter
• A condensing lens
• Manual or automatic intensity control circuit (shutter).
Lamp (Bulb)
Lamp or bulb is the most important part of the light source. When the bulb fails, the entire system is out of commission until either the bulb is replaced or a new light is brought to bear. Many light sources record and display the hours of service and alert the biomedical medical engineer (or the well-informed surgeon) when it is time to make a change. When the lifetime rating of the bulb has been exceeded, the subsequent performance of the light source becomes unpredictable, often slowly dwindling until the surgeon just can not produce a well-lit scene despite the fact that bright light seems to emanate from the laparoscope.
The quality of light depends on the lamp used. Several modern types of light sources are currently available. These light sources mainly differ in the type of bulb used.
Three types of lamp are used more recently:
1. Quartz halogen Incandescent lamp
2. Xenon lamp
3. Metal halide vapor arc lamp.
I-Halogen Bulbs (150-watt) or Tungsten-halogen Bulb
It is an incandescent lamp with a transparent quartz bulb and a compressed gas filling that includes a halogen. Quartz is used instead of glass to permit higher temperatures, higher currents, and therefore greater light output. The lamp gives a brilliant light. The halogen combines with the tungsten evaporated from the hot filament to form a compound that is attracted back to the filament, thus extending the filament’s life. The halogen gas also prevents the evaporated tungsten from condensing on the bulb and darkening it, an effect that reduces the light output of ordinary incandescent lamps. First used in the late 1960s in motion-picture production, halogen lamps are now also used in automobile headlights, underwater photography, and residential lighting.
Incandescent (to begin to glow): It is so hot to the point of glowing or emitting intense light rays, like an incandescent light bulb.
Quartz, one of the most common of all rock-forming minerals and one of the most important constituents of the earth’s crust. Chemically, it is silicon dioxide, SiO2. It occurs in crystals of the hexagonal system, commonly having the form of a six-sided prism terminating in a six-sided pyramid; the crystals are often distorted and twins are common. Quartz may be transparent, translucent, or opaque; it may be colorless or colored.
The halogen lamp takes its name from the halogens included in the gas within its tungsten-filament bulb, added to prolong filament life and increase brightness.
Halogen: Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine. They are all monovalent and readily form negative ions. Halogen bulbs provide a highly efficient crisp white light source with excellent color rendering. Electrodes in halogen lamps are made of the tungsten filament. This is the only metal with a sufficiently high melting temperature and sufficient vapor pressure at elevated temperatures. They use a halogen gas that allows bulbs to burn( light) more intensely. Halogen bulbs use low voltages and have an average life of 2,000 hours. The color temperature of the halogen lamp is around (5000–5600 K). These lamps are economical and can be used for laparoscopic surgery if the low budget setup is required.
II-Xenon Lamps (300-watt)
Xenon (Symbol Xe): A colorless, odorless, highly unreactive gaseous nonmetallic element found in minute quantities in the atmosphere and extracted commercially from liquefied air. The atomic number is 54. The radioactive isotope 133Xe, having a half-life of 5.3 days, is used for diagnostic imaging in the assessment of pulmonary function, lung imaging, and cerebral blood flow studies.
Xenon lamps consist of a spherical or ellipsoidal envelope made of quartz glass, which can withstand high thermal loads and high internal pressure. For ultimate image quality, only the highest-grade clear fused silica quartz is used. It is typically doped, although not visible to the human eye, to absorb harmful UV radiation generated during operation. The color temperature of the xenon lamp is about 6000 to 6400 K. The operating pressures are tens of atmospheres at times, with surface temperatures exceeding 600°C.
The smaller, pointed electrode is called the cathode, which supplies the current to the lamp and facilitates the emission of electrons. To supply a sufficient amount of electrons, the cathode material is doped with thorium. The optimum operating temperature of the cathode tip is approximately 2000°C. To obtain this precise operating temperature, the cathode tip is pointed and in many cases has a groove on the pointed tip to act as a heat choke. This heat choke causes the tip to run at a higher temperature. This configuration of the cathode tip allows for a very high concentration of light from the cathode tip and a very stable arc.
The anode, the larger electrode, receives electrons emitted by the cathode. Once the electrons penetrate the anode face, the resulting energy is converted to heat, most of which radiates away. The large, cylindrical shape of the anode helps to keep the temperature low by radiating the heat from the anode surface.
The advantage of a xenon bulb is that it used two electrodes (cathode and anode) and there is no filament as in halogen bulb, so it has somewhat a fixed lifetime with an average of 1500 hours. The two most frequently used types of lamps are halogen and xenon. The main difference between them is in the colors obtained. The xenon lamp has a slightly bluish tint. The light emitted by the xenon lamp is more natural compared to a halogen lamp. However, most of the cameras at present analyze and compensate these variations by means of automatic “equalization of whites” (2100–10,000 K), which allows the same image to be obtained with both light sources.
A proper white balancing before the start of the operation is essential for obtaining a natural color. The white light is composed of an equal proportion of red, blue, and green colors. At the time of white balancing, the camera sets its digital coding for these primary colors to equal proportion, assuming that the target is white. If at the time of white balancing, the telescope is not seeing a perfectly white object, the setup of the camera will be incorrect and the color perception will be poor.
The newer light source of xenon is defined as a cool light but practically it is not completely heated free and it should care for ignition hazard.
III-Metal Halide Vapor Arc Lamp (250-watt)
Halide: A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide or astatide compound. Many salts are halides. All group 1 metals form halide compounds which are white solids at room temperature. A halide ion is a halogen atom bearing a negative charge. The halide ions are fluoride (F–), chloride (Cl–), bromide (Br–), iodide (I–), and astatide (At–). Such ions are present in all ionic halide salts.
Metal halides are used in high-intensity discharge lamps called metal halide lamps, such as those used in modern street lights. These are more energy-efficient than mercury- vapor lamps and have much better color rendition than orange high-pressure sodium lamps. Metal halide lamps are also commonly used in greenhouses or in rainy climates to supplement natural sunlight.
Examples of halide compounds are: sodium chloride (NaCl), potassium chloride (KCl), potassium iodide (KI), lithium chloride (LiCl), copper (II) chloride(CuCl2), silver chloride (AgCl), and chlorine fluoride (ClF).
Metal halide lamps, a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercury vapor lamp, improved luminous efficacy and light color are obtained. Originally created in the late 1960s for industrial use, metal halide lamps are now available in numerous sizes and configurations for commercial and residential applications.
Like most HID lamps, metal halide lamps operate under high pressure and temperature and require special fixtures to operate safely.
In a metal halide lamp, a mixture of compounds (comprising mostly salts of rare earth and halides as well as the mercury which provides the conduction path) is carefully chosen to produce an output that approximates to ‘white’ light as perceived by the human eye. There is two types of metal halide lamp generally used. They are iron iodide lamps and gallium iodide lamps. Iron iodide is a broad emitter and enhances the spectral output of the lamp in the 380 nm. Gallium iodide has the effect of introducing spectral lines at 403 nm and 417 nm of the electromagnetic spectrum.
The intensity of the light delivered by any lamp also depends on the power supply of the source. However, increasing power poses a real problem as it generates more heat. At present, the improvements made to the cameras means that it is possible to return to reasonable power levels of 250 W. However, 400 W units are preferable in order to obtain sufficient illumination of the abdomen even when bleeding causes strong light absorption. It is important to remember that a three-chip camera requires more light than the single-chip camera so a 400 W light source is recommended for 3 chips cameras.
IV-LED light source
LED technology is rapidly becoming the modern-day benchmark for illumination. The new range of LED light source units is available offering high performance, quality, durability, and economy. The economy is due to the longevity of the lamp units. For example, at an average of 30,000 hours operating life, the LED units offer years of trouble-free performance as well as the inherent cost saving of replacement bulbs. At an average of 30,000 hours, the operating life of LED light sources exceeds the standard life of high-performance light sources. 250 workdays per year at 10 hours each equals an operating life of approx. 10-12 years. Most incandescent and halogen bulbs are in the Kelvin range 2700K-3000K. Fluorescent, metal halide, and LED bulbs can be purchased with color temperature options from 2700K to 6500K.
Why LED light source?
LEDs offer definite advantages over conventional lamps:
1. Purchase costs are quickly justified due to the long life (30,000 hours) and minimal power consumption
2. Extremely economical
3. Ultra-low maintenance
4. Clear return on investment
5. High energy efficiency with 90% reduced power consumption over conventional bulb types
6. Ready to go, instantly (full light intensity available as soon as the unit is powered on)
7. Environmentally friendly
Heat Filter
For 100 percent of the energy consumed, a normal light source (a light bulb) converts approximately two percent to light and 98 percent as heat. This heat is mainly due to the infrared spectrum of light and due to obstruction in the pathway of light. If infrared travels through the light cable, the cable will become hot. A heat filter is introduced to filter this infrared in fiberoptic cable. A cool light source lowers this ratio by creating more light but does not reduce the heat produced to zero. This implies a significant dissipation of heat, which increases as the power rating increases. A cold light is a light emitted at low temperatures from a source that is not incandescent, such as fluorescence or phosphorescence. Incandescence is the emission of light (visible electromagnetic radiation) from a hot body as a result of its temperature.
The sources are protected against transmitting too much heat at present. The heat is essentially dissipated in transport, along the cable, in the connection with the endoscope and along with the endoscope. While it is remarkable how little heat is delivered to the tip of the laparoscope, the effects are cumulative. A lighted laparoscope or fiberoptic bundle in direct contact with paper drapes or the patient’s skin will cause a burn after 20 or 30 seconds and must be avoided. Some accidents have been reported due to burning caused by the heat of the optics system. It is therefore important to test the equipment, particularly if assemblies of different brands are used.
Condensing Lens
The purpose of the condensing lens is to converge the light emitted by lamp to the area of light cable input. In most of the light source, it is used for increasing the light intensity per square cm of area.
Manual or Automatic Intensity Control Circuit (Shutter)
Manual adjustment allows the light source to be adjusted to a power level defined by the surgeon. In video cameras, close-up viewing is hampered in too much light, whereas a more distant view is too dark. To address this, the luminosity of most of the current light sources is adjustable. The advanced light source system is based on the automatic intensity adjustment technology. The video camera transforms the signal into an electronic signal. This electronic signal is coded in order to be transported. The coding dissociates the luminance and chrominance of the image. The luminance is the quantity of light of the signal (black and white) that dictates the quality of the final image. When there is too much light for the image (when the endoscope is near to the tissue), the luminance signal of the oscilloscope increases. On the other hand, when the luminosity is low (distant view or red surroundings), the luminance is low and the electronic signal is much weaker. A good quality luminance signal is calibrated to one millivolt. Overexposed images make the electronic signal pass above one millivolt, whereas underexposed images make the signal drop below one millivolt. Light sources equipped with adjustment analyze the luminance. If the signal is significantly higher than one millivolt, they lower the power and bring the signal back within the standards. Conversely, if the signal is too weak, they increase their intensity.
These systems are extremely valuable, permitting work to be performed at different distances from the target in good viewing conditions. However, the cameras currently available are often equipped with a regulation system, which is capable of automatic gain control in poor light conditions and the purchase of a light source with adjustment associated with a camera equipped with an adjustment system is a double purchase that is unnecessary. A laparoscopic surgeon should be technically well-acknowledged by the principle of the instrument they are using. The purchase of a costly instrument is not an answer for achieving a good task, ability to handle them is equally important.
Infrared Light Source: The new infrared LED light source provides real-time endoscopic visibility and near-infrared fluorescence imaging. This enables the surgeon to perform minimally invasive surgery using standard endoscopic visible light as well as visual assessment of vessels, blood flow, related tissue perfusion, and biliary anatomy near-infrared imaging. In addition, this infrared visualization technology is very useful to transilluminate the ureters with the fibreoptic ureteric kit (IRIS U-kits) available.
LIGHT CABLE
Minimal access surgery depends on the artificial light available in the closed body cavity, and before the discovery of light source and light cable; mirrors were used to reflect the light onto the subject where direct light access was not possible.
In 1954, a major breakthrough in technology occurred in the development of fiberoptic cables. The principle of fiberoptic cable was based on the total internal reflection of light. Light can be conducted along a curved glass rod due to multiple total internal reflections. Light would enter at one end of the fiber and emerge at the other end after numerous internal reflections with virtually all of its intensity.
Total Internal Reflection
An effect that combines both refraction and reflection is total internal reflection. Consider light coming from a dense medium like water into a less dense medium like air. When the light coming from the water strikes the surface, the part will be reflected and part will be refracted. Measured with respect to the normal line perpendicular to the surface, the reflected light comes off at an angle equal to that at which it entered, while that for the refracted light is larger than the incident angle. In fact the greater the incident angle, the more the refracted light bends away from the normal. Thus, increasing the angle of incidence from path “1” to “2” will eventually reach a point where the refracted angle is 90o, at which point the light appears to emerge along the surface between the water and air. If the angle of incidence is increased further, the refracted light cannot leave the water. It gets completely reflected. The interesting thing about total internal reflection is that it really is total. That is 100 percent of the light gets reflected back into the more dense medium, as long as the angle at which it is incident to the surface is large enough.
The light enters the glass cable, and as long as the bending is not too sudden, it will be totally internally reflected when it hits the sides, and thus is guided along the cable. This is used in telephone and TV cables to carry the signals. Light as an information carrier is much faster and more efficient than electrons in an electric current. Also, since light rays do not interact with each other (whereas electrons interact via their electric charge), it is possible to pack a large number of different light signals into the same fiberoptics cable without distortion. You are probably most familiar with fiberoptics cables in novelty items consisting of thin, multi-colored strands of glass that carry light beams. Nowadays, there are two types of light cable available:
1. Fiberoptic cable
2. Liquid crystal gel cable.
Fiberoptic Cable
Fiberoptic is the science or technology of light transmission through (a bundle of optical fibers) very fine, flexible glass or plastic fibers.
Fiberoptic cables are made up of a bundle of optical fiberglass thread swaged at both ends. The fiber size used is usually 20 to 150 micron in diameter. A good fiberoptic cable will transmit all the spectrum of light without loss. They have a very high quality of optical transmission but are fragile.
The light inside these fibers travels on the principle of total internal reflection without losing much of its intensity. The multimode fiber maintains the intensity of light and the light can be passed in a curved path of the light cable.
As the light cables are used progressively, some optical fibers break. The loss of optical fibers may be seen when one end of the cable is viewed in daylight. The broken fibers are seen as black spots. To avoid the breakage of these fibers, the curvature radius of light cable should be respected and in any circumstances, it should not be less than 15 cm in radius. If the heat filter or cooling system of the light source does not work properly, the fibers of these light cables are burnt (melt) and it will decrease the intensity of light dramatically. If poor quality fibers are used, it might burn just within a few months of use.
Liquid Crystal Gel Cable
These cables are made up of a sheath that is filled with a clear optical gel (Liquid crystal). Crystal (a clear, transparent mineral or glass resembling ice) is a piece of solid substance, such as quartz, with regular shape in which plane faces intersect at definite angles, due to the regular internal structure of its atoms, ions, or molecules. Within a crystal, many identical paralleled-piped unit cells, each containing a group of atoms, are packed together to fill all space (see illustration). In scientific nomenclature, the term crystal is usually short for single crystal, a single periodic arrangement of atoms. Most gems are single crystals. However, many materials are polycrystalline, consisting of many small grains, each of which is a single crystal. For example, most metals are polycrystalline.
Liquid Crystal
A substance that flows like a liquid but maintains some of the ordered structure characteristics of a crystal. Some organic substances do not melt directly when heated but instead turn from a crystalline solid to a liquid crystalline state. When heated further, a true liquid is formed. Liquid crystals have unique properties. The structures are easily affected by changes in mechanical stress, electromagnetic fields, temperature, and chemical environment.
Liquid Crystal Gel Cables are capable of transmitting up to 30 percent more light than optic fibers. Due to lighter and better color temperature transmission, this cable is recommended in those circumstances, where documentation (movie, photography, or TV) is performed. The quartz swaging at the ends is extremely fragile, especially when the cable is hot. The slightest shock, on a bench, for example, can cause the quartz end to crack and thus cause a loss in the transmission of the light.
Gel cables transmit more heat than optical fiber cables. These cables are made more rigid by a metal sheath, which makes them more difficult to maintain and to store. In conclusion, even though the choice is a difficult one, we use optical fiber cables, which are as fragile as the gel cables but their flexibility makes them much easier to maintain.
Attachment of the Light Cable to the Light Source
The conventional attachment has at right angle connection for light source and camera. Recently, new attachment for light cable is available known as DCI interface (Display control interface). The benefit of this is that it maintains upright orientation regardless of the angle of viewing, using an auto- rotation system. It also provides single-handed control of the entire endoscope camera system.
Maintenance of Light Cable
The following points should be followed for the maintenance of light cable:
• Handle them carefully.
• Avoid twisting them.
• After the operation has been completed, the cable should preferably be first disconnected from the endoscope and then disconnected from the light source. In fact, most of the sources currently available have a plug for holding the cable until it cools down.
• The end of the crystal of cable should be periodically cleaned with a cotton swab moistened with alcohol.
• The outer plastic covering of the cable should be cleaned with a mild cleaning agent or disinfectant.
• Distal end of the fiberoptic cable should never be placed on or under drapes, or next to the patient, when connected to an illuminated light source. The heat generated from the intensity of the light may cause burns to the patient or ignite the drapes.
• The intensity of the light source is so high that there is a chance of retinal damage if the light will fall directly on the eye. Never try to look directly at the light source when it is lighted.
TELESCOPE
There are two types of telescope, rigid and flexible. The rigid laparoscopic and thoracoscopic telescopes come in a variety of shapes and sizes and offering several different angles of view. The standard laparoscope consists of a metal shaft between 24 to 33 cm in length.
There are three important structural differences in telescope available in the market:
• No. of the rod lens: From 6 to 18-rod lens system telescopes
• The Angle of view: Between 0° and 120° telescopes
• The Diameter: 1.5 to 15 mm of telescopes.
The Angle of View
Telescopes offer either a straight-on view with the 0° or can be angled at 25 to 30 or 45 to 50°. The 30° telescope provides a total field of view of 152° compared with the 0° telescope, which only provides a field of view of 76°. The 30° forward oblique angle permits far greater latitude for viewing underlying areas under difficult anatomical conditions.
The Diameter
The most commonly used telescope has a diameter of 10 mm and provides the greatest light and visual acuity. The next most commonly used telescope is the 5 mm laparoscope, which can be placed through one of the working ports for an alternative view. Smaller-diameter laparoscopes, down to a 1.1 mm scope, are available and are used mostly in children. They are not used commonly in adult patients because of an inability to direct enough light into the larger abdominal cavity. Laparoscopes are as small as 1 mm have been produced for diagnostic use. The field of view and picture brightness are dramatic improvements over early designs. “Mini” or “ Micro” 2 mm laparoscopy is reported for diagnostic and even advanced procedures. One of the problems with working with these smaller laparoscopes (particularly those less than 3.4 mm) is that they tend to bend easily, leading to potential damage during surgery. Fullscreen 5 mm laparoscopes with images comparable to many 10 mm systems are now available.
The Lens System
There are two lens system designs used with the laparoscopy. The conventional thin lens system and the Hopkins rod- lens system design. The thin lens system, which uses a series of objective lenses to transport the image down the laparoscope, is used less commonly. The Hopkins lens system containing a series of quartz-rod lenses that carry the image through the length of the scope to the eyepiece. Rigid rod lens system provides good resolution and better depth perception. The Hopkins lens system uses more glass than air so it has improved light transmission. Normally used telescope is the Hopkins Forward Oblique Telescope (30°). Its diameter is 10 mm length of 33 cm and is autoclavable.
At the distal end, it is a front lens complex (inverting real-image lens system, IRILS) which creates an inverted and real image of the subject. A number of IRILS transport the image to the eyepiece containing a magnifying lens. In the Hopkins rod-lens system, light is transmitted through glass columns and refracted through intervening air lenses. The camera is attached to the eyepiece of the laparoscope for processing.
Digital laparoscopes, in which the laparoscope and camera head are a single unit with the imaging sensor at the end of the laparoscope, have been available since the early 1990s. This (chip on stick technology) has been introduced in which Charge-coupling device-chip (CCD) will be at the tip inside the abdominal cavity. One of the popular brands of the digital laparoscope is Olympus EndoEye The ENDOEYE comes with a fog-free feature, providing clear views throughout the procedure. The advanced multi-CCD chip on the tip technology enables bright, clear images, and Narrow Band Imaging (NBI) further enhances the visualization of vessels and other tissues on the mucosal surface. The flexible tip can articulate in all directions up to 100°, and the focus-free optical design provides greater depth of field, eliminating the need for manual focusing.
Telescope Fiber Bundle
The telescope also contains a parallel optical fibers bundle that transmits light into the abdomen from the light source via a light cable attached to the side of the telescope. The fiber bundle in the laparoscope and the fiberoptic light cable must be in excellent working order so as to achieve an optimal well-lighted picture. The fiber bundle located along a track on the periphery of the telescope and occupies less than half of the circumference of the telescope. Is an exit at the inner tip of the telescope is corresponding to the attachment of the light cable to the side of the telescope?
3D Stereoscope
One of the main problems associated with video-assisted MIS is the loss of stereopsis, meaning the perception of depth and three-dimensionality. This occurs when a three-dimensional (3D) image is projected on a two-dimensional screen and is often the cause of impeded hand-eye coordination and erroneous movements of the tools. Modern laparoscopic stereoscope with dual cameras can provide 3D images in ultra-high definition resolution and offer a binocular stereoscopic vision of the operative field comparable to open surgery, making up for the loss of stereovision and representing a definite improvement. There are flexible 3D videoscopes also available which allow the surgeon to reach hidden targets even through tortuous paths and have permitted the emergence of novel techniques that exploit the body's natural openings. In addition, video images can be enhanced with virtual models of structures and tissues, creating an augmented reality environment that has been proven to improve the performance of the surgeon. These new 3D technologies, also used to create completely virtual scenes for surgical preparation and training, are rendered from volumetric data that are obtained from preoperative scans.
The Olympus VISERA 3D platforms (Olympus, Shinjuku, Tokyo, Japan), for instance, include stereo videoscopes that can bend their tip of 100° in four directions and providing 3D videos in 4K resolution and offering flexibility for applications in laparoscopy and endoscopy. Another example is the 3D-Eye-Flex, developed by Nishiyama et al,15 an endoscopic video system that offers a wide-angle of view for minimally invasive neurosurgery. This type of technology is already commercially available and has undergone clinical trials, yielding improved performance, shorter learning curve, and greater accuracy and precision.
LAPAROSCOPIC CAMERA
The first medical camera was introduced by Circon Corporation in 1972. The laparoscopic camera is one of the very important instruments and should be of good quality. Laparoscopic camera available is either of a single chip or three chips. We all know that there are three primary colors (Red, green, and blue). All the colors are a mixture of these three primary colors in different proportions.
The Charge-coupling device (Chip) (CCD)or CMOS (Complementary Metal Oxide Semiconductor) is an electronic memory that records the intensity of light as a variable charge. Widely used in still cameras, camcorders, and scanners to capture images, CCDs are analog devices. Their charges equate to shades of light for monochrome images or shades of red, green, and blue when used with color filters. Three chips camera uses three CCDs, one for each of the red, green, and blue colors.
Why Coupled?
The “coupled” in the name is because the CCD is comprised of an array of imaging pixels and a matching array of storage pixels that are coupled together. After the imaging array is exposed to light, its charges are quickly transferred to the storage array. While the imaging CCDs are being exposed to the next picture, the storage CCDs from the last picture is being read out a row at a time to the analog-to-digital converters (A/D converters) that transform the charges into binary data( 0/1) to be processed. CCD and CMOS are both image sensors found in digital laparoscopic cameras. They're what's responsible for converting light into electronic signals. The first digital cameras used CCD (Charged Coupling Devices) to turn images from analog light signals into digital pixels. They're made through a special manufacturing process that allows the conversion to take place in the chip without distortion. This creates high-quality sensors that produce excellent images. But, because they require special manufacturing, they are more expensive than their newer CMOS counterparts. CMOS (Complementary Metal Oxide Semiconductor) chips use transistors at each pixel to move the charge through traditional wires. This offers flexibility because each pixel is treated individually. Traditional manufacturing processes are used to make CMOS. It's the same as creating microchips. Because they're easier to produce, CMOS sensors are cheaper than CCD sensors. Because CMOS technology came after CCD sensors and are cheaper to manufacture, CMOS sensors are the reason that laparoscopic cameras have dropped in price.
The biggest difference is that CCD sensors create high-quality images with low noise. CMOS images tend to be higher in noise. CCD sensors are more sensitive to light. CMOS sensors need more light to create a low noise image at proper exposure. This does not mean that CMOS sensors are completely inferior to CCD. CCD has been around for a lot longer in digital cameras, and the technology is more advanced. CMOS sensors are catching up and will soon match CCD in terms of resolution and overall quality. They can be manufactured on any standard silicon production line and are much more inexpensive when compared to CCD sensors. Eventually, economics will someday make every camera CMOS when the final advances in quality are made. In fact, CMOS sensors are already superior to CCD sensors in terms of power consumption.
In a camera, CCD or CMOS takes the place of film. They are exposed to light, recording the intensities, or shades of light as variable charges. In the digital camera above, the variable, analog charges in the CCD, or CMOS are converted to binary data (0/1) by analog-to Digital converter chip (ADC). DSP: Digital single processing
The camera system has two components: The head of the camera, which is attached to the ocular of the telescope, and the controller, which is usually located on the trolley along with the monitor. Within the head of the camera is an objective zoom lens that focuses the image of the object on the chip, and a CCD chip that “sees” an image taken by the telescope. All modern miniature cameras used in minimal access surgery are based on the charged-couple device (chip) (CCD). The CCD then converts the optical image into an electrical signal that is sent through the camera cable to CCU (Camera control unit). The chip has light-sensitive photoreceptors that generate pixels by transforming the incoming photons into electronic charges. The electronic charges are then transferred from the pixels into a storage element on the chip. A subsequent scanning at defined time intervals results in a black and white image with gray tones.
Pixel: PIX [picture]+ EL[element], picture element is the smallest element of a light-sensitive device, such as cameras that use charge-coupled devices. It is the smallest resolved unit of a video image that has specific luminescence and color. Its proportions are determined by the number of lines making up the scanning raster (the pattern of dots that form the image) and the resolution along each line. In the most common form of computer graphics and the CCD devices, the thousands of tiny pixels that make up an individual image are projected onto a display screen as illuminated dots that from a distance appear as a continuous image. An electron beam creates the grid of pixels by tracing each horizontal line from left to right, one pixel at a time, from the top line to the bottom line.
The number of pixels determines the resolution. Screen resolution is rated by the number of horizontal and vertical pixels; for example, 1024 × 768 means 1,024 pixels are displayed in each row, and there are 768 rows (lines). Likewise, bitmapped images are sized in pixels: a 350 × 250 image has 350 pixels across and 250 down. You've probably already noticed the jump from pre-digital 'standard definition' television up to 'HD' and 'Full HD' services that are now available on digital TV, online streaming, and Blu-Ray discs. Compared to earlier standards, this HD footage is detailed, crisp and it even looks good when viewed on a large TV. But even the best quality, '1080p' HD footage is only 1920 pixels across. Recently 4 K or UHD laparoscopic cameras are available. 4K is significantly more detailed, since it has twice as many pixels horizontally, and four times as many pixels in total.
Pixels and Subpixels: In monochrome systems, the pixel is the smallest addressable unit. With color systems, each pixel contains red, green, and blue subpixels, and the subpixel is the smallest addressable unit for the screen’s electronic circuits. On a display screen, pixels are either phosphorus or liquid crystal elements. For monochrome, the element is either energized fully or not. For grayscale, the pixel is energized with different intensities, creating a range from light to dark. For color displays, the red, green, and blue (RGB) subpixels are each energized to a particular intensity, and the combination of the three color intensities creates the perceived color to the eye. The average chip contains 250000 to 380000 pixels but 4K video is poised to become the new benchmark for both recording and watching the laparoscopic video and it brings a whole host of benefits, right away.
Cameras are classified according to the number of chips. These differ among other things, in the way they relay color information to the monitor. Color separation is used to create a colored video image from the original black and white. In single-chip cameras, color separation is achieved by adding a stripe filter that covers the whole chip. Each stripe accepts one of the complementary colors (magenta, green, cyan, or yellow) and each pixel is assigned to one stripe.
In a single-chip camera, these three primary colors are sensed by a single chip. In a three-chip camera, there are 3 CCD chips for separate capture and processing of three primary colors (R, G, B colors). In three-chip cameras, color separation is achieved with a prism system that overlies the chips. Each chip receives only one of the three primary colors (Red, green, or blue). This system gives a higher resolution and better image quality because the pixel number is three times greater.
The video information, color, and light are scanned at a rate of 525 lines per frame and 30 frames per second. Picture resolution determines the clarity and detail of the video image. Higher the resolution, the better will be the quality of the image. The resolution of the picture is ascertained by the number of distinct vertical lines that can be seen in the picture. The higher the resolution numbers, the sharper, and cleaner the image will form. The CCU of the camera is connected with the monitor and the monitor converts the electrical image back to the original optical image. These 3 chip camera has unprecedented color reproduction and the highest degree of fidelity. Three chip cameras have a high horizontal image resolution of more than 750 lines.
The chip on Stick Technology
Currently, chip on stick technology has been introduced in which CCD will be at the tip inside the abdominal cavity. It is proved that the resolution of the picture will be more than 250 k pixels.
Focusing on Laparoscopic Camera
The laparoscopic camera needs to be focused before inserting inside the abdominal cavity. At the time of focusing, it should be placed at a distance of approximately 10 cm away from the target for the 10 mm telescope, 5 mm for 5 mm telescope, and 4 mm for 4 mm telescope, with an average distance of approximately 5 mm for all telescopes. This distance is optimum for focusing because at the time of laparoscopic surgery, most of the time we keep the telescope at this distance.
White Balancing of Camera
White balancing should be performed before inserting the camera inside the abdominal cavity. White balancing is required to remove added impurities of light which unknowingly we add. During white balancing digital laparoscopic camera will added counter color to neutralize our added impurity. White balancing is necessary every time before the start of surgery because every time there is some added impurities of color due to the following variables:
• Difference in voltage
• Differences in color temperature of light sources
• Different cleaning material used to clean the tip of the telescope which can stain the tip
• Scratches, wear and tear of the telescopes eye-piece, object piece, and CCD of camera.
White balancing is done by keeping any white object in front of a telescope attached with a camera that senses white object as reference. It adjusts its primary color (Red, blue and green) to make a pure natural white color.
LAPAROSCOPIC VIDEO MONITOR
Surgical monitors are slightly different from the TV which we watch at home. Monitor lasts long so a surgeon gets high-end products with at least 600 lines resolution. The size of the screen varies generally from 8 to 29 inches. The closure the laparoscopic surgeon is to the monitor, the smaller the monitor should be to get a better picture. The basic principle of image reproduction is horizontal beam scanning on the face of the picture tube. This plate is coated internally with a fluorescent substance containing phosphorus. This generates electrons when struck by beams from the electron gun. As the beam sweeps horizontally and back, it covers all the picture elements before reaching its original position. This occurs repetitively and rapidly. This method is called ‘ Horizontal linear scanning’. Each picture frame consists of several such lines depending on the type of system used. The distance of the monitor from the eye of the surgeon should be five-time to the diagonal length of the monitor screen. This means if the monitor is 21 inch it should be kept 105 inches away from the eye of the surgeon. Nowadays 4K laparoscopic monitor is preferred, It is also known as an ultra-high-definition or UHD monitor, is one that supports 4K resolution. This brings up another common question: what is 4K resolution? The answer is simple. Standard high-definition, or 1080P (as found on Blu-ray discs and HD televisions), is made up of a picture that is 1,920 pixels in width and 1,080 pixels in height. In total, this results in a picture with more than two million pixels. The width of a picture that has 4K resolution contains almost 4,000 pixels (3,840 to be precise – twice that of 1080P). With 2,160 pixels along the vertical side, the total number of pixels on a 4K monitor is four times that of a traditional HD monitor.
Endoscopic Vision (Video) Technology Evolution
In the past endoscopic procedures were done without the aid of monitors. The operator visualized the interiors of the patient directly through the eyepiece of the scope. This method was associated with many difficulties. He was the only person who could observe the procedure leading to poor coordination with other members of the team. As a result, extensive and difficult procedures could not be performed. The magnification was very poor. Surgeons had to face problems with posture leading to discomfort and strain as his eye was always glued to the eyepiece. He had difficulties in orientation due to visualizing with only one eye.
As better methods of communication developed the introduction of television brought about a significant impact. A good magnification of the image was reproduced. All members of the team could visualize the procedure. Surgeons could operate more comfortably. Complex procedures began to be undertaken and were even recorded. Soulas in France first used television for endoscopic procedures in 1956. He demonstrated the first televised bronchoscopy. A rigid bronchoscope was attached to a black and white camera that weighed about 100 lbs.
In 1959, a laparoscopic procedure was demonstrated using a closed-circuit television program using the “Forestier method”. This method was developed by transmitting an intense beam of light along a quartz rod from the proximal to distal ends of the laparoscope. The first miniature endoscopic black and white television camera was developed in Australia in 1960. It weighed 350 grams, was 45 mm wide, and 120 mm long. Because of its small dimensions, it could be attached to the eyepiece.
TELEVISION SYSTEMS
The existing television systems in use differ according to the country. The USA uses the NTSC (National Television System Committee) system. In European countries, the PAL (Phase alternation by line) system is in use. There is also a French system called SECAM (Sequential Color and Memory). The final image depends upon the number of lines of resolution, scanning lines, pixels, and dot.pitch. The number of black and white lines a system can differentiate gives the lines of resolution. These can be horizontal and vertical. The horizontal resolution is the number of vertical lines that can be seen and vice versa. Pixels denote the picture elements and they are responsible for picture resolution. The more number of pixels is, the better the resolution. They are represented on the camera chip by an individual photodiode. The restricting factor of information on a scan line is the ‘dot pitch’ that represents phosphorus element size.
The NTSC system has certain drawbacks. Not all the lines of resolution are used. The maximum number of lines visible is reduced by 40. Improving the resolution of the camera will not improve monitor resolution. This is due to a fixed vertical resolution. In addition to these problems, if the phase angle is disturbed even a little, it produces unwanted hues. The PAL system is superior in certain aspects. It can overcome this problem by producing alternations over the axis of modulation of the color signed by line. This system also deals with problems of flickering. It involves a process called ‘interlacing’ where odd and even lines in a field are scanned alternatively. The SECAM system is similar to PAL in these aspects except that the signals are transmitted in sequence.
The Formation of the Color Image
Another important aspect one has to keep in mind is the formation of the color image. This is done by superimposing the data for color on the existing black and white pictures. The black and white signal is a monochromatic signal and combines with the composite color signal. This gives the final color signal. Luminance (brightness) is delivered by the black and white signal. Chrominance (color) is delivered by the color signal. It is called composite as it contains the three primary color information (Red, blue, and green). A system that combines luminance and chrominance into one signal is called a “ compound system”.
Color values can be problematic as they can go out of phase. This is due to their high sensitivity. Applying a reference mark for the signal on the scanning line called “ color burst” can prevent this. The color on a monitor can be calibrated. This can be done manually by using the standard color bars of NTSC or by using other methods like “blue gun”. New monitors do not require this, as calibration can be done automatically.
Monitor Connecting Cables
Images cannot be visualized on the monitor unless they are wired. Monitor cables are of three types. The RGB cable has 3 wires, one for each primary color. The Y/C cable has 2 wires, one for the luminance (Y) and one for the chrominance (C) component. The composite cable consists of one pair of wires. An important factor to realize is that no matter what type of cable is used, whether it has better bandwidth or other advantages, the final resolution depends upon the monitor used. For HD and UHD system we should always use DVI or HDMI cable. DVI, which stands for Digital Visual Interface, is the older of the two and arguably on its way out. Functionally, HDMI and DVI cords are basically identical. The DVI video signal is basically the same as HDMI, just without the audio. In laparoscopic surgery, we don’t use audio so DVI is used more.
Frames of Reference in Vision
We face many problems with monitors in regard to minimal access surgery. But before dealing with them, a mention of the frames of reference in vision would be apt. NJ Wade’s paper on ‘Frames of reference in vision’ mentions various frames namely ethnocentric, egocentric, geocentric, and pattern centric. He applies these to minimal access surgery and finds a dissociation of pattern centric motion (seen on the monitor) and the area of manipulation. Any visual-motor task requires a match between the coordinate systems operating in both vision and motor control. Knowledge of these frames can alter our perspective of the way things happen in minimal access surgery with respect to vision.
Imaging Technical Terms
Resolution means the degree of sharpness of a displayed or printed image; simply, the ability of a television or film image to reproduce fine detail. Resolution is defined as (Pixels per inch); the maximum number of pixels that can be displayed on a screen monitor, expressed as (number of horizontal pixels) × (number of vertical pixels), i.e. 1024 × 768. The ratio of horizontal to vertical resolution is usually 4:3, the same as that of conventional television sets.
For a monitor, a screen resolution of 1920 × 1200 means 1,920 pixels horizontally across each of 1,200 lines, which run vertically from top to bottom. For printers and scanners, the resolution is expressed as the number of dots per linear inch (Printed dots per inch- dpi). 300 dpi means 300 × 300 or 90,000 dots per square inch. Laser printers and plotters have resolutions from 300 to 1,200 dpi and more, whereas most display screens provide less than 100 dpi.
Gain controls the brightness of the image under conditions of low light by recruiting pixels to increase signal strength. Clearly, this step results in some loss of image resolution. This increases light but results in a grainy picture with poorer resolution. It also may create a loss of color accuracy owing to the amplification of the noise-to-signal ratio). The gain should be off at the beginning of a routine procedure (not needed in routine situations). There are two good reasons for this. First, inadequate light at the beginning of the procedure is an indication that a piece of equipment is malfunctioning, a situation that should be rectified before getting too involved with the procedure. Second, the use of “gain” comes at the expense of picture resolution, resulting in a somewhat grainy image on the monitor, while turning the brightness knob to maximum produces a very washed- out picture. A good general rule of thumb to follow is to look in the right upper quadrant and visualize the space over the liver. The entire dome of the liver and right lateral diaphragm should be well lit and easily seen. If not, then the lighting system should be evaluated and optimized prior to beginning the dissection.
Contrast: The extent to which adjacent areas of an optical image, on a monitor screen, differ in brightness. It is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. Because the human visual system is more sensitive to contrast than absolute luminescence, we can perceive the world similarly regardless of the huge changes in illumination over the day or from place-to-place.
Luminescence is a general term applied to all forms of cool light, i.e. light emitted by sources other than a hot, incandescent body. It is a process by which an excited material emits light in a process not caused solely by a rise in temperature. The excitation is usually achieved with, ultraviolet radiation, X-rays, electrons, alpha particles, electrical fields, or chemical energy. The color or wavelength, of the light emitted, is determined by the material, while the intensity depends on both the material and the input energy. Examples of luminescence include light emissions from neon lamps, luminescent watch dials, television and computer screens, fluorescent lamps, and fireflies.
Modulation Transfer Function
The endoscopes transmit resolution and contrast to the monitor. The efficacy by which this occurs determines the more delicate aspects of the image. Resolution and contrast can be measured on a specially designed optical bench and expressed as modulation transfer function (MTF). If there is excessive glare in the picture then contrast and resolution decrease. Distortions of the image can occur and if these lines seem to curve outwards they are called “ barrel distortion”. Field curvature occurs when there is an improper focus of the center from other parts. Astigmatism can occur when some lines of different orientations are present in focus and others are not.
Temporal Aliasing
When a moving object is shown on a monitor, unless the speed with which it is moving is similar to the refresh rate, then jerky movements will occur. This is called “ temporal aliasing”. This can be prevented by the use of filters, or by performing slow movements. Fatigue and headache can occur due to disturbance of saccadic eye movements. These are rapid eye movements used to visualize the borders of a field.
Gaze-Down Position
When a surgeon has to constantly look in a different direction and operate in another his efficiency to perform declines. The job becomes even more difficult if the monitor is positioned at a further distance, giving rise to spatial disorientation. A surgeon can perform optimally if he can look and operate in the same direction as in open surgery. This can also be called the “ gaze-down position”.
THREE-DIMENSIONAL VISION
One of the major limitations of minimal access surgery is the loss of depth perception. The surgeon works with artificial two-dimensional video pictures available on the monitor. There is a need to develop some mechanism to improve depth perception or stereoscopic vision. Stereoscopic vision is needed for precise and fast complex manipulations because the perception of space and depth is necessary for surgery.
Stereopsis (3D Perception)
Stereopsis refers to the perception of three-dimensional shape from any source of depth information. Unlike horses, humans have two eyes located side-by-side in the front of their heads. Due to the close side-by-side positioning, each eye takes a view of the same area from a slightly different angle.
The two eyes have different views of the visual world and these different views set-up disparities that give us information about the relative depth of the image that is the third dimension of vision. Binocular disparity results when an image of an object falls on different areas of the two retinas
It is well known that laparoscopy is the consequence of advances made in the field of medical engineering. Each surgical specialty has different requirements for instruments. Laparoscopy was initially criticized owing to the cost of specialized instruments and possible complications due to these sharp long instruments. Also, it necessitated difficult hand-eye coordination. Gradually, the technique gained recognition and respect from the medical fraternity since it drastically reduced many of the complications of the open procedure.
Minimal access surgery has developed rapidly only after the grand success of laparoscopic cholecystectomy. Computer-aided designing of laparoscopic instruments is an important branch of medical engineering. It is now possible to control access through microprocessor controlled laparoscopic instruments. New procedures and instruments are innovated regularly which makes it important for the surgeon to be familiar with the developments. Laparoscopy is a technologically dependent surgery and it is expected every surgeon should have reasonably good knowledge of these instruments.
LAPAROSCOPIC TROLLEY
The mobile laparoscopic video cart is equipped with locking brakes and has four anti-static rollers. The trolley has a drawer and three shelves. The upper shelves have a tilt adjustment and used for supporting the video monitor unit. Included on the trolley is an electrical supply terminal strip, mounted on the rear of the second shelf (from the top). Recently, ceiling-mounted trolleys are launched by many companies that are ergonomically better and consume less space in the operation theater.
IMAGING SYSTEMS
• Light source
• Light cable
• Telescope
• Laparoscopic camera
• Laparoscopic video monitor
The imaging system is a chain of equipment that are link together in place perfectly and functioning well to produce an excellent laparoscopic image. The break-in this sequential pass of links of the chain will be rendered our imaging system impotent.
The classic imaging chain starts with a light source, and ends in the monitor, requiring seven pieces of equipment, known as the Magnificent Seven: light source, fiberoptic light cable, laparoscope, camera head, video signal processor, video cable, and monitor. This imaging chain is often supported by a cast of VCRs, photo printers, or digital capture devices. The surgeon and the operating room team must work together to ensure optimal equipment function through careful handling of the equipment in the operating room and during the sterilization process. Yet, when the image is poor, many operating teams become paralyzed, unable to function without the aid of a medical engineer. “Understanding can overcome any situation, however, mysterious or insurmountable, it may appear to be.” Accordingly, understanding the (imaging) video system will allow the operating surgeon to do the basic troubleshooting for his or her system and not be totally dependent on nursing or technical staff, especially at night when experienced personnel may not be available. The advent of integrated operating suites has not changed the principles of this basic idea.
LIGHT SOURCE
It is clear and easy to say that, life, recently, is impossible without light, and simply: no light, no laparoscopy. The light source is the often-overlooked soldier of the video laparoscopic system.
A high-intensity light is created with bulbs of halogen gas, xenon gas, or mercury vapor. The bulbs are available in different wattages “150 and 300 Watt” and should be chosen based on the type of procedure being performed. Because light is absorbed by the blood, any procedure in which bleeding is encountered may require more light. We use stronger light sources for all advanced laparoscopy. The availability of light is a challenge in many bariatric procedures where the abdominal cavity is large.
A good laparoscopic light source should emit light as much as possible near the natural sunlight.
Three types of the light source are in use today:
1. Halogen light source
2. Xenon light source
3. Metal halide light source
The output from the light sources is conducted to the telescope by light cables that contain either glass fiber bundles or special fluid. The halogen light source is used in the medical field for the last 20 years, but the spectral temperature of these lights is 3200 Kelvin which makes it too different and too low from natural sunlight. The midday sunlight has approximately 5600 Kelvin color temperature. In practice, the yellow light of the halogen bulb is compensated for in the video camera system by white balancing.
A more suitable light source for laparoscopic cameras involves the creation of an electrical arc in a metal halide system or in xenon. This electrical arc is produced in the same way as in a flash of the photographic camera. Xenon has a more natural color spectrum and a smaller spot size than halogen. The xenon light source emits a spectral temperature of the color of approximately 6000 Kelvin on average for a power of 300 W
Arc generated lamps have a spectral temperature that gradually decreases with use and white balance is required before each use. The bulb needs replacing after 250 to 500 hours of usage, depending on the type of lamp. One of the main advantages of the laparoscopy is that of obtaining a virtually microsurgical view compared to that obtained by laparotomy. The quality of the image obtained very much depends on the quantity of light available at each step of the optical and electronic system.
The Interface of the laparoscopic teamwork with a Standard Light Source:
It is essential for the laparoscopic team, particularly the surgeons, to know about all the switch and function of the light source. All essential details of the equipment and all the action required on the part can be found on the operating manual of the product.
Many light sources record and display the hours of service and alert the biomedical medical engineer (or the well- informed surgeon) when it is time to make a change. When the lifetime rating of the bulb has been exceeded, the subsequent performance of the light source becomes unpredictable, often slowly dwindling until the surgeon just can not produce a well-lit scene despite the fact that bright light seems to emanate from the laparoscope.
A typical light source consists of:
• A lamp (bulb)
• A heat filter
• A condensing lens
• Manual or automatic intensity control circuit (shutter).
Lamp (Bulb)
Lamp or bulb is the most important part of the light source. When the bulb fails, the entire system is out of commission until either the bulb is replaced or a new light is brought to bear. Many light sources record and display the hours of service and alert the biomedical medical engineer (or the well-informed surgeon) when it is time to make a change. When the lifetime rating of the bulb has been exceeded, the subsequent performance of the light source becomes unpredictable, often slowly dwindling until the surgeon just can not produce a well-lit scene despite the fact that bright light seems to emanate from the laparoscope.
The quality of light depends on the lamp used. Several modern types of light sources are currently available. These light sources mainly differ in the type of bulb used.
Three types of lamp are used more recently:
1. Quartz halogen Incandescent lamp
2. Xenon lamp
3. Metal halide vapor arc lamp.
I-Halogen Bulbs (150-watt) or Tungsten-halogen Bulb
It is an incandescent lamp with a transparent quartz bulb and a compressed gas filling that includes a halogen. Quartz is used instead of glass to permit higher temperatures, higher currents, and therefore greater light output. The lamp gives a brilliant light. The halogen combines with the tungsten evaporated from the hot filament to form a compound that is attracted back to the filament, thus extending the filament’s life. The halogen gas also prevents the evaporated tungsten from condensing on the bulb and darkening it, an effect that reduces the light output of ordinary incandescent lamps. First used in the late 1960s in motion-picture production, halogen lamps are now also used in automobile headlights, underwater photography, and residential lighting.
Incandescent (to begin to glow): It is so hot to the point of glowing or emitting intense light rays, like an incandescent light bulb.
Quartz, one of the most common of all rock-forming minerals and one of the most important constituents of the earth’s crust. Chemically, it is silicon dioxide, SiO2. It occurs in crystals of the hexagonal system, commonly having the form of a six-sided prism terminating in a six-sided pyramid; the crystals are often distorted and twins are common. Quartz may be transparent, translucent, or opaque; it may be colorless or colored.
The halogen lamp takes its name from the halogens included in the gas within its tungsten-filament bulb, added to prolong filament life and increase brightness.
Halogen: Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine. They are all monovalent and readily form negative ions. Halogen bulbs provide a highly efficient crisp white light source with excellent color rendering. Electrodes in halogen lamps are made of the tungsten filament. This is the only metal with a sufficiently high melting temperature and sufficient vapor pressure at elevated temperatures. They use a halogen gas that allows bulbs to burn( light) more intensely. Halogen bulbs use low voltages and have an average life of 2,000 hours. The color temperature of the halogen lamp is around (5000–5600 K). These lamps are economical and can be used for laparoscopic surgery if the low budget setup is required.
II-Xenon Lamps (300-watt)
Xenon (Symbol Xe): A colorless, odorless, highly unreactive gaseous nonmetallic element found in minute quantities in the atmosphere and extracted commercially from liquefied air. The atomic number is 54. The radioactive isotope 133Xe, having a half-life of 5.3 days, is used for diagnostic imaging in the assessment of pulmonary function, lung imaging, and cerebral blood flow studies.
Xenon lamps consist of a spherical or ellipsoidal envelope made of quartz glass, which can withstand high thermal loads and high internal pressure. For ultimate image quality, only the highest-grade clear fused silica quartz is used. It is typically doped, although not visible to the human eye, to absorb harmful UV radiation generated during operation. The color temperature of the xenon lamp is about 6000 to 6400 K. The operating pressures are tens of atmospheres at times, with surface temperatures exceeding 600°C.
The smaller, pointed electrode is called the cathode, which supplies the current to the lamp and facilitates the emission of electrons. To supply a sufficient amount of electrons, the cathode material is doped with thorium. The optimum operating temperature of the cathode tip is approximately 2000°C. To obtain this precise operating temperature, the cathode tip is pointed and in many cases has a groove on the pointed tip to act as a heat choke. This heat choke causes the tip to run at a higher temperature. This configuration of the cathode tip allows for a very high concentration of light from the cathode tip and a very stable arc.
The anode, the larger electrode, receives electrons emitted by the cathode. Once the electrons penetrate the anode face, the resulting energy is converted to heat, most of which radiates away. The large, cylindrical shape of the anode helps to keep the temperature low by radiating the heat from the anode surface.
The advantage of a xenon bulb is that it used two electrodes (cathode and anode) and there is no filament as in halogen bulb, so it has somewhat a fixed lifetime with an average of 1500 hours. The two most frequently used types of lamps are halogen and xenon. The main difference between them is in the colors obtained. The xenon lamp has a slightly bluish tint. The light emitted by the xenon lamp is more natural compared to a halogen lamp. However, most of the cameras at present analyze and compensate these variations by means of automatic “equalization of whites” (2100–10,000 K), which allows the same image to be obtained with both light sources.
A proper white balancing before the start of the operation is essential for obtaining a natural color. The white light is composed of an equal proportion of red, blue, and green colors. At the time of white balancing, the camera sets its digital coding for these primary colors to equal proportion, assuming that the target is white. If at the time of white balancing, the telescope is not seeing a perfectly white object, the setup of the camera will be incorrect and the color perception will be poor.
The newer light source of xenon is defined as a cool light but practically it is not completely heated free and it should care for ignition hazard.
III-Metal Halide Vapor Arc Lamp (250-watt)
Halide: A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide or astatide compound. Many salts are halides. All group 1 metals form halide compounds which are white solids at room temperature. A halide ion is a halogen atom bearing a negative charge. The halide ions are fluoride (F–), chloride (Cl–), bromide (Br–), iodide (I–), and astatide (At–). Such ions are present in all ionic halide salts.
Metal halides are used in high-intensity discharge lamps called metal halide lamps, such as those used in modern street lights. These are more energy-efficient than mercury- vapor lamps and have much better color rendition than orange high-pressure sodium lamps. Metal halide lamps are also commonly used in greenhouses or in rainy climates to supplement natural sunlight.
Examples of halide compounds are: sodium chloride (NaCl), potassium chloride (KCl), potassium iodide (KI), lithium chloride (LiCl), copper (II) chloride(CuCl2), silver chloride (AgCl), and chlorine fluoride (ClF).
Metal halide lamps, a member of the high-intensity discharge (HID) family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercury vapor lamp, improved luminous efficacy and light color are obtained. Originally created in the late 1960s for industrial use, metal halide lamps are now available in numerous sizes and configurations for commercial and residential applications.
Like most HID lamps, metal halide lamps operate under high pressure and temperature and require special fixtures to operate safely.
In a metal halide lamp, a mixture of compounds (comprising mostly salts of rare earth and halides as well as the mercury which provides the conduction path) is carefully chosen to produce an output that approximates to ‘white’ light as perceived by the human eye. There is two types of metal halide lamp generally used. They are iron iodide lamps and gallium iodide lamps. Iron iodide is a broad emitter and enhances the spectral output of the lamp in the 380 nm. Gallium iodide has the effect of introducing spectral lines at 403 nm and 417 nm of the electromagnetic spectrum.
The intensity of the light delivered by any lamp also depends on the power supply of the source. However, increasing power poses a real problem as it generates more heat. At present, the improvements made to the cameras means that it is possible to return to reasonable power levels of 250 W. However, 400 W units are preferable in order to obtain sufficient illumination of the abdomen even when bleeding causes strong light absorption. It is important to remember that a three-chip camera requires more light than the single-chip camera so a 400 W light source is recommended for 3 chips cameras.
IV-LED light source
LED technology is rapidly becoming the modern-day benchmark for illumination. The new range of LED light source units is available offering high performance, quality, durability, and economy. The economy is due to the longevity of the lamp units. For example, at an average of 30,000 hours operating life, the LED units offer years of trouble-free performance as well as the inherent cost saving of replacement bulbs. At an average of 30,000 hours, the operating life of LED light sources exceeds the standard life of high-performance light sources. 250 workdays per year at 10 hours each equals an operating life of approx. 10-12 years. Most incandescent and halogen bulbs are in the Kelvin range 2700K-3000K. Fluorescent, metal halide, and LED bulbs can be purchased with color temperature options from 2700K to 6500K.
Why LED light source?
LEDs offer definite advantages over conventional lamps:
1. Purchase costs are quickly justified due to the long life (30,000 hours) and minimal power consumption
2. Extremely economical
3. Ultra-low maintenance
4. Clear return on investment
5. High energy efficiency with 90% reduced power consumption over conventional bulb types
6. Ready to go, instantly (full light intensity available as soon as the unit is powered on)
7. Environmentally friendly
Heat Filter
For 100 percent of the energy consumed, a normal light source (a light bulb) converts approximately two percent to light and 98 percent as heat. This heat is mainly due to the infrared spectrum of light and due to obstruction in the pathway of light. If infrared travels through the light cable, the cable will become hot. A heat filter is introduced to filter this infrared in fiberoptic cable. A cool light source lowers this ratio by creating more light but does not reduce the heat produced to zero. This implies a significant dissipation of heat, which increases as the power rating increases. A cold light is a light emitted at low temperatures from a source that is not incandescent, such as fluorescence or phosphorescence. Incandescence is the emission of light (visible electromagnetic radiation) from a hot body as a result of its temperature.
The sources are protected against transmitting too much heat at present. The heat is essentially dissipated in transport, along the cable, in the connection with the endoscope and along with the endoscope. While it is remarkable how little heat is delivered to the tip of the laparoscope, the effects are cumulative. A lighted laparoscope or fiberoptic bundle in direct contact with paper drapes or the patient’s skin will cause a burn after 20 or 30 seconds and must be avoided. Some accidents have been reported due to burning caused by the heat of the optics system. It is therefore important to test the equipment, particularly if assemblies of different brands are used.
Condensing Lens
The purpose of the condensing lens is to converge the light emitted by lamp to the area of light cable input. In most of the light source, it is used for increasing the light intensity per square cm of area.
Manual or Automatic Intensity Control Circuit (Shutter)
Manual adjustment allows the light source to be adjusted to a power level defined by the surgeon. In video cameras, close-up viewing is hampered in too much light, whereas a more distant view is too dark. To address this, the luminosity of most of the current light sources is adjustable. The advanced light source system is based on the automatic intensity adjustment technology. The video camera transforms the signal into an electronic signal. This electronic signal is coded in order to be transported. The coding dissociates the luminance and chrominance of the image. The luminance is the quantity of light of the signal (black and white) that dictates the quality of the final image. When there is too much light for the image (when the endoscope is near to the tissue), the luminance signal of the oscilloscope increases. On the other hand, when the luminosity is low (distant view or red surroundings), the luminance is low and the electronic signal is much weaker. A good quality luminance signal is calibrated to one millivolt. Overexposed images make the electronic signal pass above one millivolt, whereas underexposed images make the signal drop below one millivolt. Light sources equipped with adjustment analyze the luminance. If the signal is significantly higher than one millivolt, they lower the power and bring the signal back within the standards. Conversely, if the signal is too weak, they increase their intensity.
These systems are extremely valuable, permitting work to be performed at different distances from the target in good viewing conditions. However, the cameras currently available are often equipped with a regulation system, which is capable of automatic gain control in poor light conditions and the purchase of a light source with adjustment associated with a camera equipped with an adjustment system is a double purchase that is unnecessary. A laparoscopic surgeon should be technically well-acknowledged by the principle of the instrument they are using. The purchase of a costly instrument is not an answer for achieving a good task, ability to handle them is equally important.
Infrared Light Source: The new infrared LED light source provides real-time endoscopic visibility and near-infrared fluorescence imaging. This enables the surgeon to perform minimally invasive surgery using standard endoscopic visible light as well as visual assessment of vessels, blood flow, related tissue perfusion, and biliary anatomy near-infrared imaging. In addition, this infrared visualization technology is very useful to transilluminate the ureters with the fibreoptic ureteric kit (IRIS U-kits) available.
LIGHT CABLE
Minimal access surgery depends on the artificial light available in the closed body cavity, and before the discovery of light source and light cable; mirrors were used to reflect the light onto the subject where direct light access was not possible.
In 1954, a major breakthrough in technology occurred in the development of fiberoptic cables. The principle of fiberoptic cable was based on the total internal reflection of light. Light can be conducted along a curved glass rod due to multiple total internal reflections. Light would enter at one end of the fiber and emerge at the other end after numerous internal reflections with virtually all of its intensity.
Total Internal Reflection
An effect that combines both refraction and reflection is total internal reflection. Consider light coming from a dense medium like water into a less dense medium like air. When the light coming from the water strikes the surface, the part will be reflected and part will be refracted. Measured with respect to the normal line perpendicular to the surface, the reflected light comes off at an angle equal to that at which it entered, while that for the refracted light is larger than the incident angle. In fact the greater the incident angle, the more the refracted light bends away from the normal. Thus, increasing the angle of incidence from path “1” to “2” will eventually reach a point where the refracted angle is 90o, at which point the light appears to emerge along the surface between the water and air. If the angle of incidence is increased further, the refracted light cannot leave the water. It gets completely reflected. The interesting thing about total internal reflection is that it really is total. That is 100 percent of the light gets reflected back into the more dense medium, as long as the angle at which it is incident to the surface is large enough.
The light enters the glass cable, and as long as the bending is not too sudden, it will be totally internally reflected when it hits the sides, and thus is guided along the cable. This is used in telephone and TV cables to carry the signals. Light as an information carrier is much faster and more efficient than electrons in an electric current. Also, since light rays do not interact with each other (whereas electrons interact via their electric charge), it is possible to pack a large number of different light signals into the same fiberoptics cable without distortion. You are probably most familiar with fiberoptics cables in novelty items consisting of thin, multi-colored strands of glass that carry light beams. Nowadays, there are two types of light cable available:
1. Fiberoptic cable
2. Liquid crystal gel cable.
Fiberoptic Cable
Fiberoptic is the science or technology of light transmission through (a bundle of optical fibers) very fine, flexible glass or plastic fibers.
Fiberoptic cables are made up of a bundle of optical fiberglass thread swaged at both ends. The fiber size used is usually 20 to 150 micron in diameter. A good fiberoptic cable will transmit all the spectrum of light without loss. They have a very high quality of optical transmission but are fragile.
The light inside these fibers travels on the principle of total internal reflection without losing much of its intensity. The multimode fiber maintains the intensity of light and the light can be passed in a curved path of the light cable.
As the light cables are used progressively, some optical fibers break. The loss of optical fibers may be seen when one end of the cable is viewed in daylight. The broken fibers are seen as black spots. To avoid the breakage of these fibers, the curvature radius of light cable should be respected and in any circumstances, it should not be less than 15 cm in radius. If the heat filter or cooling system of the light source does not work properly, the fibers of these light cables are burnt (melt) and it will decrease the intensity of light dramatically. If poor quality fibers are used, it might burn just within a few months of use.
Liquid Crystal Gel Cable
These cables are made up of a sheath that is filled with a clear optical gel (Liquid crystal). Crystal (a clear, transparent mineral or glass resembling ice) is a piece of solid substance, such as quartz, with regular shape in which plane faces intersect at definite angles, due to the regular internal structure of its atoms, ions, or molecules. Within a crystal, many identical paralleled-piped unit cells, each containing a group of atoms, are packed together to fill all space (see illustration). In scientific nomenclature, the term crystal is usually short for single crystal, a single periodic arrangement of atoms. Most gems are single crystals. However, many materials are polycrystalline, consisting of many small grains, each of which is a single crystal. For example, most metals are polycrystalline.
Liquid Crystal
A substance that flows like a liquid but maintains some of the ordered structure characteristics of a crystal. Some organic substances do not melt directly when heated but instead turn from a crystalline solid to a liquid crystalline state. When heated further, a true liquid is formed. Liquid crystals have unique properties. The structures are easily affected by changes in mechanical stress, electromagnetic fields, temperature, and chemical environment.
Liquid Crystal Gel Cables are capable of transmitting up to 30 percent more light than optic fibers. Due to lighter and better color temperature transmission, this cable is recommended in those circumstances, where documentation (movie, photography, or TV) is performed. The quartz swaging at the ends is extremely fragile, especially when the cable is hot. The slightest shock, on a bench, for example, can cause the quartz end to crack and thus cause a loss in the transmission of the light.
Gel cables transmit more heat than optical fiber cables. These cables are made more rigid by a metal sheath, which makes them more difficult to maintain and to store. In conclusion, even though the choice is a difficult one, we use optical fiber cables, which are as fragile as the gel cables but their flexibility makes them much easier to maintain.
Attachment of the Light Cable to the Light Source
The conventional attachment has at right angle connection for light source and camera. Recently, new attachment for light cable is available known as DCI interface (Display control interface). The benefit of this is that it maintains upright orientation regardless of the angle of viewing, using an auto- rotation system. It also provides single-handed control of the entire endoscope camera system.
Maintenance of Light Cable
The following points should be followed for the maintenance of light cable:
• Handle them carefully.
• Avoid twisting them.
• After the operation has been completed, the cable should preferably be first disconnected from the endoscope and then disconnected from the light source. In fact, most of the sources currently available have a plug for holding the cable until it cools down.
• The end of the crystal of cable should be periodically cleaned with a cotton swab moistened with alcohol.
• The outer plastic covering of the cable should be cleaned with a mild cleaning agent or disinfectant.
• Distal end of the fiberoptic cable should never be placed on or under drapes, or next to the patient, when connected to an illuminated light source. The heat generated from the intensity of the light may cause burns to the patient or ignite the drapes.
• The intensity of the light source is so high that there is a chance of retinal damage if the light will fall directly on the eye. Never try to look directly at the light source when it is lighted.
TELESCOPE
There are two types of telescope, rigid and flexible. The rigid laparoscopic and thoracoscopic telescopes come in a variety of shapes and sizes and offering several different angles of view. The standard laparoscope consists of a metal shaft between 24 to 33 cm in length.
There are three important structural differences in telescope available in the market:
• No. of the rod lens: From 6 to 18-rod lens system telescopes
• The Angle of view: Between 0° and 120° telescopes
• The Diameter: 1.5 to 15 mm of telescopes.
The Angle of View
Telescopes offer either a straight-on view with the 0° or can be angled at 25 to 30 or 45 to 50°. The 30° telescope provides a total field of view of 152° compared with the 0° telescope, which only provides a field of view of 76°. The 30° forward oblique angle permits far greater latitude for viewing underlying areas under difficult anatomical conditions.
The Diameter
The most commonly used telescope has a diameter of 10 mm and provides the greatest light and visual acuity. The next most commonly used telescope is the 5 mm laparoscope, which can be placed through one of the working ports for an alternative view. Smaller-diameter laparoscopes, down to a 1.1 mm scope, are available and are used mostly in children. They are not used commonly in adult patients because of an inability to direct enough light into the larger abdominal cavity. Laparoscopes are as small as 1 mm have been produced for diagnostic use. The field of view and picture brightness are dramatic improvements over early designs. “Mini” or “ Micro” 2 mm laparoscopy is reported for diagnostic and even advanced procedures. One of the problems with working with these smaller laparoscopes (particularly those less than 3.4 mm) is that they tend to bend easily, leading to potential damage during surgery. Fullscreen 5 mm laparoscopes with images comparable to many 10 mm systems are now available.
The Lens System
There are two lens system designs used with the laparoscopy. The conventional thin lens system and the Hopkins rod- lens system design. The thin lens system, which uses a series of objective lenses to transport the image down the laparoscope, is used less commonly. The Hopkins lens system containing a series of quartz-rod lenses that carry the image through the length of the scope to the eyepiece. Rigid rod lens system provides good resolution and better depth perception. The Hopkins lens system uses more glass than air so it has improved light transmission. Normally used telescope is the Hopkins Forward Oblique Telescope (30°). Its diameter is 10 mm length of 33 cm and is autoclavable.
At the distal end, it is a front lens complex (inverting real-image lens system, IRILS) which creates an inverted and real image of the subject. A number of IRILS transport the image to the eyepiece containing a magnifying lens. In the Hopkins rod-lens system, light is transmitted through glass columns and refracted through intervening air lenses. The camera is attached to the eyepiece of the laparoscope for processing.
Digital laparoscopes, in which the laparoscope and camera head are a single unit with the imaging sensor at the end of the laparoscope, have been available since the early 1990s. This (chip on stick technology) has been introduced in which Charge-coupling device-chip (CCD) will be at the tip inside the abdominal cavity. One of the popular brands of the digital laparoscope is Olympus EndoEye The ENDOEYE comes with a fog-free feature, providing clear views throughout the procedure. The advanced multi-CCD chip on the tip technology enables bright, clear images, and Narrow Band Imaging (NBI) further enhances the visualization of vessels and other tissues on the mucosal surface. The flexible tip can articulate in all directions up to 100°, and the focus-free optical design provides greater depth of field, eliminating the need for manual focusing.
Telescope Fiber Bundle
The telescope also contains a parallel optical fibers bundle that transmits light into the abdomen from the light source via a light cable attached to the side of the telescope. The fiber bundle in the laparoscope and the fiberoptic light cable must be in excellent working order so as to achieve an optimal well-lighted picture. The fiber bundle located along a track on the periphery of the telescope and occupies less than half of the circumference of the telescope. Is an exit at the inner tip of the telescope is corresponding to the attachment of the light cable to the side of the telescope?
3D Stereoscope
One of the main problems associated with video-assisted MIS is the loss of stereopsis, meaning the perception of depth and three-dimensionality. This occurs when a three-dimensional (3D) image is projected on a two-dimensional screen and is often the cause of impeded hand-eye coordination and erroneous movements of the tools. Modern laparoscopic stereoscope with dual cameras can provide 3D images in ultra-high definition resolution and offer a binocular stereoscopic vision of the operative field comparable to open surgery, making up for the loss of stereovision and representing a definite improvement. There are flexible 3D videoscopes also available which allow the surgeon to reach hidden targets even through tortuous paths and have permitted the emergence of novel techniques that exploit the body's natural openings. In addition, video images can be enhanced with virtual models of structures and tissues, creating an augmented reality environment that has been proven to improve the performance of the surgeon. These new 3D technologies, also used to create completely virtual scenes for surgical preparation and training, are rendered from volumetric data that are obtained from preoperative scans.
The Olympus VISERA 3D platforms (Olympus, Shinjuku, Tokyo, Japan), for instance, include stereo videoscopes that can bend their tip of 100° in four directions and providing 3D videos in 4K resolution and offering flexibility for applications in laparoscopy and endoscopy. Another example is the 3D-Eye-Flex, developed by Nishiyama et al,15 an endoscopic video system that offers a wide-angle of view for minimally invasive neurosurgery. This type of technology is already commercially available and has undergone clinical trials, yielding improved performance, shorter learning curve, and greater accuracy and precision.
LAPAROSCOPIC CAMERA
The first medical camera was introduced by Circon Corporation in 1972. The laparoscopic camera is one of the very important instruments and should be of good quality. Laparoscopic camera available is either of a single chip or three chips. We all know that there are three primary colors (Red, green, and blue). All the colors are a mixture of these three primary colors in different proportions.
The Charge-coupling device (Chip) (CCD)or CMOS (Complementary Metal Oxide Semiconductor) is an electronic memory that records the intensity of light as a variable charge. Widely used in still cameras, camcorders, and scanners to capture images, CCDs are analog devices. Their charges equate to shades of light for monochrome images or shades of red, green, and blue when used with color filters. Three chips camera uses three CCDs, one for each of the red, green, and blue colors.
Why Coupled?
The “coupled” in the name is because the CCD is comprised of an array of imaging pixels and a matching array of storage pixels that are coupled together. After the imaging array is exposed to light, its charges are quickly transferred to the storage array. While the imaging CCDs are being exposed to the next picture, the storage CCDs from the last picture is being read out a row at a time to the analog-to-digital converters (A/D converters) that transform the charges into binary data( 0/1) to be processed. CCD and CMOS are both image sensors found in digital laparoscopic cameras. They're what's responsible for converting light into electronic signals. The first digital cameras used CCD (Charged Coupling Devices) to turn images from analog light signals into digital pixels. They're made through a special manufacturing process that allows the conversion to take place in the chip without distortion. This creates high-quality sensors that produce excellent images. But, because they require special manufacturing, they are more expensive than their newer CMOS counterparts. CMOS (Complementary Metal Oxide Semiconductor) chips use transistors at each pixel to move the charge through traditional wires. This offers flexibility because each pixel is treated individually. Traditional manufacturing processes are used to make CMOS. It's the same as creating microchips. Because they're easier to produce, CMOS sensors are cheaper than CCD sensors. Because CMOS technology came after CCD sensors and are cheaper to manufacture, CMOS sensors are the reason that laparoscopic cameras have dropped in price.
The biggest difference is that CCD sensors create high-quality images with low noise. CMOS images tend to be higher in noise. CCD sensors are more sensitive to light. CMOS sensors need more light to create a low noise image at proper exposure. This does not mean that CMOS sensors are completely inferior to CCD. CCD has been around for a lot longer in digital cameras, and the technology is more advanced. CMOS sensors are catching up and will soon match CCD in terms of resolution and overall quality. They can be manufactured on any standard silicon production line and are much more inexpensive when compared to CCD sensors. Eventually, economics will someday make every camera CMOS when the final advances in quality are made. In fact, CMOS sensors are already superior to CCD sensors in terms of power consumption.
In a camera, CCD or CMOS takes the place of film. They are exposed to light, recording the intensities, or shades of light as variable charges. In the digital camera above, the variable, analog charges in the CCD, or CMOS are converted to binary data (0/1) by analog-to Digital converter chip (ADC). DSP: Digital single processing
The camera system has two components: The head of the camera, which is attached to the ocular of the telescope, and the controller, which is usually located on the trolley along with the monitor. Within the head of the camera is an objective zoom lens that focuses the image of the object on the chip, and a CCD chip that “sees” an image taken by the telescope. All modern miniature cameras used in minimal access surgery are based on the charged-couple device (chip) (CCD). The CCD then converts the optical image into an electrical signal that is sent through the camera cable to CCU (Camera control unit). The chip has light-sensitive photoreceptors that generate pixels by transforming the incoming photons into electronic charges. The electronic charges are then transferred from the pixels into a storage element on the chip. A subsequent scanning at defined time intervals results in a black and white image with gray tones.
Pixel: PIX [picture]+ EL[element], picture element is the smallest element of a light-sensitive device, such as cameras that use charge-coupled devices. It is the smallest resolved unit of a video image that has specific luminescence and color. Its proportions are determined by the number of lines making up the scanning raster (the pattern of dots that form the image) and the resolution along each line. In the most common form of computer graphics and the CCD devices, the thousands of tiny pixels that make up an individual image are projected onto a display screen as illuminated dots that from a distance appear as a continuous image. An electron beam creates the grid of pixels by tracing each horizontal line from left to right, one pixel at a time, from the top line to the bottom line.
The number of pixels determines the resolution. Screen resolution is rated by the number of horizontal and vertical pixels; for example, 1024 × 768 means 1,024 pixels are displayed in each row, and there are 768 rows (lines). Likewise, bitmapped images are sized in pixels: a 350 × 250 image has 350 pixels across and 250 down. You've probably already noticed the jump from pre-digital 'standard definition' television up to 'HD' and 'Full HD' services that are now available on digital TV, online streaming, and Blu-Ray discs. Compared to earlier standards, this HD footage is detailed, crisp and it even looks good when viewed on a large TV. But even the best quality, '1080p' HD footage is only 1920 pixels across. Recently 4 K or UHD laparoscopic cameras are available. 4K is significantly more detailed, since it has twice as many pixels horizontally, and four times as many pixels in total.
Pixels and Subpixels: In monochrome systems, the pixel is the smallest addressable unit. With color systems, each pixel contains red, green, and blue subpixels, and the subpixel is the smallest addressable unit for the screen’s electronic circuits. On a display screen, pixels are either phosphorus or liquid crystal elements. For monochrome, the element is either energized fully or not. For grayscale, the pixel is energized with different intensities, creating a range from light to dark. For color displays, the red, green, and blue (RGB) subpixels are each energized to a particular intensity, and the combination of the three color intensities creates the perceived color to the eye. The average chip contains 250000 to 380000 pixels but 4K video is poised to become the new benchmark for both recording and watching the laparoscopic video and it brings a whole host of benefits, right away.
Cameras are classified according to the number of chips. These differ among other things, in the way they relay color information to the monitor. Color separation is used to create a colored video image from the original black and white. In single-chip cameras, color separation is achieved by adding a stripe filter that covers the whole chip. Each stripe accepts one of the complementary colors (magenta, green, cyan, or yellow) and each pixel is assigned to one stripe.
In a single-chip camera, these three primary colors are sensed by a single chip. In a three-chip camera, there are 3 CCD chips for separate capture and processing of three primary colors (R, G, B colors). In three-chip cameras, color separation is achieved with a prism system that overlies the chips. Each chip receives only one of the three primary colors (Red, green, or blue). This system gives a higher resolution and better image quality because the pixel number is three times greater.
The video information, color, and light are scanned at a rate of 525 lines per frame and 30 frames per second. Picture resolution determines the clarity and detail of the video image. Higher the resolution, the better will be the quality of the image. The resolution of the picture is ascertained by the number of distinct vertical lines that can be seen in the picture. The higher the resolution numbers, the sharper, and cleaner the image will form. The CCU of the camera is connected with the monitor and the monitor converts the electrical image back to the original optical image. These 3 chip camera has unprecedented color reproduction and the highest degree of fidelity. Three chip cameras have a high horizontal image resolution of more than 750 lines.
The chip on Stick Technology
Currently, chip on stick technology has been introduced in which CCD will be at the tip inside the abdominal cavity. It is proved that the resolution of the picture will be more than 250 k pixels.
Focusing on Laparoscopic Camera
The laparoscopic camera needs to be focused before inserting inside the abdominal cavity. At the time of focusing, it should be placed at a distance of approximately 10 cm away from the target for the 10 mm telescope, 5 mm for 5 mm telescope, and 4 mm for 4 mm telescope, with an average distance of approximately 5 mm for all telescopes. This distance is optimum for focusing because at the time of laparoscopic surgery, most of the time we keep the telescope at this distance.
White Balancing of Camera
White balancing should be performed before inserting the camera inside the abdominal cavity. White balancing is required to remove added impurities of light which unknowingly we add. During white balancing digital laparoscopic camera will added counter color to neutralize our added impurity. White balancing is necessary every time before the start of surgery because every time there is some added impurities of color due to the following variables:
• Difference in voltage
• Differences in color temperature of light sources
• Different cleaning material used to clean the tip of the telescope which can stain the tip
• Scratches, wear and tear of the telescopes eye-piece, object piece, and CCD of camera.
White balancing is done by keeping any white object in front of a telescope attached with a camera that senses white object as reference. It adjusts its primary color (Red, blue and green) to make a pure natural white color.
LAPAROSCOPIC VIDEO MONITOR
Surgical monitors are slightly different from the TV which we watch at home. Monitor lasts long so a surgeon gets high-end products with at least 600 lines resolution. The size of the screen varies generally from 8 to 29 inches. The closure the laparoscopic surgeon is to the monitor, the smaller the monitor should be to get a better picture. The basic principle of image reproduction is horizontal beam scanning on the face of the picture tube. This plate is coated internally with a fluorescent substance containing phosphorus. This generates electrons when struck by beams from the electron gun. As the beam sweeps horizontally and back, it covers all the picture elements before reaching its original position. This occurs repetitively and rapidly. This method is called ‘ Horizontal linear scanning’. Each picture frame consists of several such lines depending on the type of system used. The distance of the monitor from the eye of the surgeon should be five-time to the diagonal length of the monitor screen. This means if the monitor is 21 inch it should be kept 105 inches away from the eye of the surgeon. Nowadays 4K laparoscopic monitor is preferred, It is also known as an ultra-high-definition or UHD monitor, is one that supports 4K resolution. This brings up another common question: what is 4K resolution? The answer is simple. Standard high-definition, or 1080P (as found on Blu-ray discs and HD televisions), is made up of a picture that is 1,920 pixels in width and 1,080 pixels in height. In total, this results in a picture with more than two million pixels. The width of a picture that has 4K resolution contains almost 4,000 pixels (3,840 to be precise – twice that of 1080P). With 2,160 pixels along the vertical side, the total number of pixels on a 4K monitor is four times that of a traditional HD monitor.
Endoscopic Vision (Video) Technology Evolution
In the past endoscopic procedures were done without the aid of monitors. The operator visualized the interiors of the patient directly through the eyepiece of the scope. This method was associated with many difficulties. He was the only person who could observe the procedure leading to poor coordination with other members of the team. As a result, extensive and difficult procedures could not be performed. The magnification was very poor. Surgeons had to face problems with posture leading to discomfort and strain as his eye was always glued to the eyepiece. He had difficulties in orientation due to visualizing with only one eye.
As better methods of communication developed the introduction of television brought about a significant impact. A good magnification of the image was reproduced. All members of the team could visualize the procedure. Surgeons could operate more comfortably. Complex procedures began to be undertaken and were even recorded. Soulas in France first used television for endoscopic procedures in 1956. He demonstrated the first televised bronchoscopy. A rigid bronchoscope was attached to a black and white camera that weighed about 100 lbs.
In 1959, a laparoscopic procedure was demonstrated using a closed-circuit television program using the “Forestier method”. This method was developed by transmitting an intense beam of light along a quartz rod from the proximal to distal ends of the laparoscope. The first miniature endoscopic black and white television camera was developed in Australia in 1960. It weighed 350 grams, was 45 mm wide, and 120 mm long. Because of its small dimensions, it could be attached to the eyepiece.
TELEVISION SYSTEMS
The existing television systems in use differ according to the country. The USA uses the NTSC (National Television System Committee) system. In European countries, the PAL (Phase alternation by line) system is in use. There is also a French system called SECAM (Sequential Color and Memory). The final image depends upon the number of lines of resolution, scanning lines, pixels, and dot.pitch. The number of black and white lines a system can differentiate gives the lines of resolution. These can be horizontal and vertical. The horizontal resolution is the number of vertical lines that can be seen and vice versa. Pixels denote the picture elements and they are responsible for picture resolution. The more number of pixels is, the better the resolution. They are represented on the camera chip by an individual photodiode. The restricting factor of information on a scan line is the ‘dot pitch’ that represents phosphorus element size.
The NTSC system has certain drawbacks. Not all the lines of resolution are used. The maximum number of lines visible is reduced by 40. Improving the resolution of the camera will not improve monitor resolution. This is due to a fixed vertical resolution. In addition to these problems, if the phase angle is disturbed even a little, it produces unwanted hues. The PAL system is superior in certain aspects. It can overcome this problem by producing alternations over the axis of modulation of the color signed by line. This system also deals with problems of flickering. It involves a process called ‘interlacing’ where odd and even lines in a field are scanned alternatively. The SECAM system is similar to PAL in these aspects except that the signals are transmitted in sequence.
The Formation of the Color Image
Another important aspect one has to keep in mind is the formation of the color image. This is done by superimposing the data for color on the existing black and white pictures. The black and white signal is a monochromatic signal and combines with the composite color signal. This gives the final color signal. Luminance (brightness) is delivered by the black and white signal. Chrominance (color) is delivered by the color signal. It is called composite as it contains the three primary color information (Red, blue, and green). A system that combines luminance and chrominance into one signal is called a “ compound system”.
Color values can be problematic as they can go out of phase. This is due to their high sensitivity. Applying a reference mark for the signal on the scanning line called “ color burst” can prevent this. The color on a monitor can be calibrated. This can be done manually by using the standard color bars of NTSC or by using other methods like “blue gun”. New monitors do not require this, as calibration can be done automatically.
Monitor Connecting Cables
Images cannot be visualized on the monitor unless they are wired. Monitor cables are of three types. The RGB cable has 3 wires, one for each primary color. The Y/C cable has 2 wires, one for the luminance (Y) and one for the chrominance (C) component. The composite cable consists of one pair of wires. An important factor to realize is that no matter what type of cable is used, whether it has better bandwidth or other advantages, the final resolution depends upon the monitor used. For HD and UHD system we should always use DVI or HDMI cable. DVI, which stands for Digital Visual Interface, is the older of the two and arguably on its way out. Functionally, HDMI and DVI cords are basically identical. The DVI video signal is basically the same as HDMI, just without the audio. In laparoscopic surgery, we don’t use audio so DVI is used more.
Frames of Reference in Vision
We face many problems with monitors in regard to minimal access surgery. But before dealing with them, a mention of the frames of reference in vision would be apt. NJ Wade’s paper on ‘Frames of reference in vision’ mentions various frames namely ethnocentric, egocentric, geocentric, and pattern centric. He applies these to minimal access surgery and finds a dissociation of pattern centric motion (seen on the monitor) and the area of manipulation. Any visual-motor task requires a match between the coordinate systems operating in both vision and motor control. Knowledge of these frames can alter our perspective of the way things happen in minimal access surgery with respect to vision.
Imaging Technical Terms
Resolution means the degree of sharpness of a displayed or printed image; simply, the ability of a television or film image to reproduce fine detail. Resolution is defined as (Pixels per inch); the maximum number of pixels that can be displayed on a screen monitor, expressed as (number of horizontal pixels) × (number of vertical pixels), i.e. 1024 × 768. The ratio of horizontal to vertical resolution is usually 4:3, the same as that of conventional television sets.
For a monitor, a screen resolution of 1920 × 1200 means 1,920 pixels horizontally across each of 1,200 lines, which run vertically from top to bottom. For printers and scanners, the resolution is expressed as the number of dots per linear inch (Printed dots per inch- dpi). 300 dpi means 300 × 300 or 90,000 dots per square inch. Laser printers and plotters have resolutions from 300 to 1,200 dpi and more, whereas most display screens provide less than 100 dpi.
Gain controls the brightness of the image under conditions of low light by recruiting pixels to increase signal strength. Clearly, this step results in some loss of image resolution. This increases light but results in a grainy picture with poorer resolution. It also may create a loss of color accuracy owing to the amplification of the noise-to-signal ratio). The gain should be off at the beginning of a routine procedure (not needed in routine situations). There are two good reasons for this. First, inadequate light at the beginning of the procedure is an indication that a piece of equipment is malfunctioning, a situation that should be rectified before getting too involved with the procedure. Second, the use of “gain” comes at the expense of picture resolution, resulting in a somewhat grainy image on the monitor, while turning the brightness knob to maximum produces a very washed- out picture. A good general rule of thumb to follow is to look in the right upper quadrant and visualize the space over the liver. The entire dome of the liver and right lateral diaphragm should be well lit and easily seen. If not, then the lighting system should be evaluated and optimized prior to beginning the dissection.
Contrast: The extent to which adjacent areas of an optical image, on a monitor screen, differ in brightness. It is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. Because the human visual system is more sensitive to contrast than absolute luminescence, we can perceive the world similarly regardless of the huge changes in illumination over the day or from place-to-place.
Luminescence is a general term applied to all forms of cool light, i.e. light emitted by sources other than a hot, incandescent body. It is a process by which an excited material emits light in a process not caused solely by a rise in temperature. The excitation is usually achieved with, ultraviolet radiation, X-rays, electrons, alpha particles, electrical fields, or chemical energy. The color or wavelength, of the light emitted, is determined by the material, while the intensity depends on both the material and the input energy. Examples of luminescence include light emissions from neon lamps, luminescent watch dials, television and computer screens, fluorescent lamps, and fireflies.
Modulation Transfer Function
The endoscopes transmit resolution and contrast to the monitor. The efficacy by which this occurs determines the more delicate aspects of the image. Resolution and contrast can be measured on a specially designed optical bench and expressed as modulation transfer function (MTF). If there is excessive glare in the picture then contrast and resolution decrease. Distortions of the image can occur and if these lines seem to curve outwards they are called “ barrel distortion”. Field curvature occurs when there is an improper focus of the center from other parts. Astigmatism can occur when some lines of different orientations are present in focus and others are not.
Temporal Aliasing
When a moving object is shown on a monitor, unless the speed with which it is moving is similar to the refresh rate, then jerky movements will occur. This is called “ temporal aliasing”. This can be prevented by the use of filters, or by performing slow movements. Fatigue and headache can occur due to disturbance of saccadic eye movements. These are rapid eye movements used to visualize the borders of a field.
Gaze-Down Position
When a surgeon has to constantly look in a different direction and operate in another his efficiency to perform declines. The job becomes even more difficult if the monitor is positioned at a further distance, giving rise to spatial disorientation. A surgeon can perform optimally if he can look and operate in the same direction as in open surgery. This can also be called the “ gaze-down position”.
THREE-DIMENSIONAL VISION
One of the major limitations of minimal access surgery is the loss of depth perception. The surgeon works with artificial two-dimensional video pictures available on the monitor. There is a need to develop some mechanism to improve depth perception or stereoscopic vision. Stereoscopic vision is needed for precise and fast complex manipulations because the perception of space and depth is necessary for surgery.
Stereopsis (3D Perception)
Stereopsis refers to the perception of three-dimensional shape from any source of depth information. Unlike horses, humans have two eyes located side-by-side in the front of their heads. Due to the close side-by-side positioning, each eye takes a view of the same area from a slightly different angle.
The two eyes have different views of the visual world and these different views set-up disparities that give us information about the relative depth of the image that is the third dimension of vision. Binocular disparity results when an image of an object falls on different areas of the two retinas
