ICG fluorescence imaging is an advanced technique in medical diagnostics and surgical guidance. This method allows medical professionals to visualize anatomical structures and physiological processes in real-time during various procedures. By providing immediate visual feedback, it enhances the clarity and precision of interventions.
How ICG Fluorescence Imaging Works
Indocyanine Green (ICG) is a water-soluble, tricarbocyanine dye used in this imaging technique. Once administered, typically through intravenous injection, ICG binds rapidly to plasma proteins within the bloodstream. It circulates throughout the body, absorbing light in the near-infrared (NIR) spectrum, specifically around 780 to 800 nanometers. This absorption causes the dye to fluoresce, emitting light at a slightly longer wavelength, usually around 820 to 850 nanometers.
Specialized cameras with filters detect this emitted near-infrared light. These cameras are designed to capture the fluorescent signal while filtering out ambient light, creating a high-contrast image. The captured fluorescent light is then processed and displayed on a monitor in real-time, allowing surgeons to observe blood flow, tissue perfusion, or the presence of specific structures that have taken up the dye. The dye remains within the vascular system and does not typically extravasate into interstitial fluid, which helps in clear visualization of blood vessels and lymphatic pathways. The liver rapidly metabolizes ICG, which is then excreted into bile without undergoing significant biotransformation.
Medical Applications of ICG Fluorescence
ICG fluorescence imaging finds extensive use across various medical disciplines due to its real-time visualization capabilities. In assessing tissue perfusion, surgeons can inject ICG and observe its flow through microvasculature. This is particularly useful in reconstructive surgery, where evaluating blood supply to tissue flaps helps ensure their viability and reduces complications like necrosis. By visualizing the distribution of the dye, areas with compromised blood flow become evident, guiding decisions on flap placement or revision.
The technique is also widely employed in identifying sentinel lymph nodes during cancer surgery. After injecting ICG near the tumor site, the dye travels through lymphatic channels, accumulating in the first lymph nodes to receive drainage from the tumor. This allows surgeons to precisely locate and remove these nodes for biopsy, aiding in accurate cancer staging and reducing the need for extensive lymph node dissection. The fluorescent signal provides a clear roadmap for identifying these nodes, which might otherwise be difficult to find visually.
In gastrointestinal surgery, ICG fluorescence aids in visualizing bile ducts during laparoscopic cholecystectomy (gallbladder removal). Injecting ICG intravenously causes it to be excreted by the liver into the bile, illuminating the bile duct system. This enhanced visualization helps surgeons avoid accidental injury to these delicate structures, a common complication during such procedures. Furthermore, ICG assists in identifying tumors and their margins in various cancers, including liver and gastric cancers. Certain tumor types can selectively accumulate ICG, making them glow under near-infrared light and distinguishing them from healthy tissue, thereby facilitating more complete resections.
Key Benefits of ICG Fluorescence Imaging
ICG fluorescence imaging provides real-time visualization during surgical procedures. This immediate feedback allows surgeons to make informed decisions dynamically, adapting their approach based on the live fluorescent images. Unlike static preoperative imaging, ICG offers a continuous assessment of anatomical structures and physiological processes throughout the operation. This real-time guidance contributes to enhanced precision during surgery, as surgeons can clearly delineate structures like blood vessels, lymphatic pathways, or tumor margins.
The enhanced clarity and precision from ICG imaging can lead to improved patient outcomes. By accurately identifying structures or assessing tissue viability, the risk of complications such as anastomotic leaks in bowel surgery or flap necrosis in reconstructive procedures can be reduced. This technology often allows for less invasive surgical approaches, as the detailed visualization can facilitate smaller incisions and more targeted interventions. Improved precision and reduced complications can lead to shorter operating times and faster patient recovery.
Safety and Important Considerations
Indocyanine Green is generally considered safe and well-tolerated. Adverse reactions are rare, with an estimated incidence of about 1 in 42,000 administrations, and are usually mild, such as skin rashes or itching. More severe reactions, like anaphylaxis, are uncommon. Patients with a known allergy to iodine or any components of the ICG dye should not receive it, as iodine is part of the dye’s chemical structure.
It is also generally avoided in patients with severe liver dysfunction, as the liver is responsible for its clearance. Before administration, medical professionals typically review a patient’s medical history for any contraindications. Once injected, ICG is rapidly cleared from the bloodstream, with a half-life of approximately 2.5 to 4 minutes in individuals with normal liver function, ensuring it does not persist in the body for extended periods.