How to Use Indocyanine Green (ICG) for Localization of Ureter

Indocyanine green (ICG) is a water-soluble, near-infrared (NIR) fluorescent dye that has gained widespread use in medical imaging, especially in urology and surgical procedures. It is employed to improve the visualization of various anatomical structures, including the ureter, during minimally invasive surgeries. The ability of ICG to fluoresce under NIR light makes it an invaluable tool for real-time imaging and enhanced localization of the ureter, facilitating safer and more precise surgical interventions.

What is Indocyanine Green (ICG)?

ICG is a diagnostic agent that, when injected into the body, binds to plasma proteins and is rapidly cleared by the liver. When exposed to NIR light, it emits fluorescence, which can be captured by specialized cameras to produce images in real-time. ICG has a unique property of being able to penetrate tissues to a certain depth while emitting a strong fluorescent signal, allowing for enhanced imaging in surgeries involving deep or complex structures like the ureter.

The main advantages of ICG over traditional contrast agents or visualization techniques are its minimal invasiveness, real-time imaging, and its ability to localize tissue structures with high precision.
 

Indications for Ureteral Localization
 

The localization of the ureter is crucial in various surgical procedures, especially in urological, gynecological, and colorectal surgeries. Some common indications for ureteral localization include:

1. Pelvic surgeries: In procedures such as hysterectomies, pelvic lymphadenectomy, or colorectal surgeries, the ureters are at risk of injury due to their location and the extensive dissection required.

2. Laparoscopic and Robotic-Assisted Surgeries: These procedures are becoming more common, and precise identification of the ureter can be challenging due to limited visual access.

3. Prevention of Ureteral Injury: Accidental injury to the ureter during surgery can lead to significant complications, such as urinary leakage or stricture formation. Using ICG can help reduce the risk of such injuries.

ICG fluorescence works by emitting light when the dye is excited by infrared light. After injection into the bloodstream, ICG binds to plasma proteins, and its fluorescence can be captured through a near-infrared camera. The process involves:

1. Excitation: When ICG is exposed to NIR light (typically around 780-800 nm), it absorbs this light and enters an excited state.

2. Fluorescence: As ICG returns to its ground state, it emits light at a longer wavelength, typically around 830-835 nm. This emitted light can be visualized through a NIR camera.

3. Imaging: Specialized equipment designed to capture NIR fluorescence images allows the surgeon to visualize the ureter in real-time during surgery, facilitating its localization.

1. Preoperative Preparation:

Patient Evaluation: Assess the patient’s overall health, renal function, and suitability for using ICG. ICG is generally safe for use in patients with normal liver and kidney function, but caution is advised in those with impaired hepatic function.

Dye Injection: ICG is injected intravenously. Typically, a dose of 0.1-0.2 mg/kg is administered. This dose is carefully calculated based on the patient’s weight and medical history.

2. Intraoperative Application:

Fluorescence Camera Setup: The surgical team must set up a near-infrared fluorescence camera and ensure it is correctly calibrated for ICG visualization.

Injection Timing: After the intravenous injection, the surgeon should wait for approximately 1-5 minutes to allow the dye to circulate and accumulate in the renal and ureteral tissues.
 

Fluorescence Visualization: Once the dye is circulated, the surgeon uses the NIR camera to visualize the fluorescence. The ureter, typically rich in blood supply, will appear as a distinct bright line on the imaging screen, facilitating its identification and precise localization.
 

3. Identification of the Ureter:

Localization: ICG fluorescence helps to identify the ureter by highlighting its anatomical location, often in real-time during dissection or other surgical maneuvers. The bright fluorescence of the ureter contrasts well with surrounding tissues.

Monitoring During Surgery: Surgeons can use the fluorescence to track the ureter’s path throughout the procedure, especially in challenging areas where the ureter is hard to distinguish from surrounding tissues, such as in the pelvis during a hysterectomy or colorectal resection.
 

4. Surgical Decision-Making:

Intraoperative Navigation: In addition to localization, ICG can guide surgical decisions, such as determining the safe distance for resection or detecting any inadvertent injury to the ureter.
 

Prevention of Injury: The real-time visualization of the ureter decreases the likelihood of accidental injury, improving patient outcomes by minimizing complications such as ureteral stricture, fistula, or extravasation.

5. Postoperative Evaluation:

Monitoring for Complications: Postoperative imaging with ICG can help evaluate ureteral integrity and identify any potential leaks, especially in cases where there was concern about injury.

Follow-up Imaging: Some institutions may choose to follow up with additional imaging studies, such as CT or MRI, to confirm the absence of injury or abnormality in the ureter.

1. Enhanced Visualization: ICG allows for real-time, high-contrast visualization of the ureter, especially in patients with a difficult pelvic anatomy.

2. Reduced Risk of Ureteral Injury: Surgeons can better identify the ureter during complex dissections, reducing the chances of accidental injury or complications.

3. Non-invasive: ICG is injected intravenously and does not require incisions, making it a safe and minimally invasive technique.

4. Real-time Imaging: Unlike traditional imaging techniques, ICG offers real-time feedback, allowing the surgeon to make immediate decisions based on live data.

While ICG has many advantages, it is important to consider some limitations:

• Not Suitable for All Patients: ICG is contraindicated in patients with iodine hypersensitivity or certain liver conditions that may affect its clearance.

• False Positives/Negatives: In rare cases, the ureter may not fluoresce adequately due to poor circulation or technical issues with the imaging equipment. Additionally, there could be interference from other nearby structures.

• Technical Skill Requirement: Surgeons and the operating team must be trained in the use of NIR fluorescence imaging and ICG injection for optimal results.

Conclusion

Indocyanine green (ICG) is a powerful tool for the localization of the ureter during surgery. By leveraging NIR fluorescence imaging, surgeons can achieve precise identification of the ureter in real-time, enhancing surgical safety and improving patient outcomes. The technique is particularly valuable in minimally invasive procedures, where anatomical structures may be difficult to visualize. While there are limitations to its use, such as patient-specific contraindications or the need for specialized equipment, the benefits of ICG in ureteral localization make it an increasingly popular choice in modern surgical practice.