Indocyanine green (ICG) imaging is a medical diagnostic technique that uses a special fluorescent dye to visualize structures and processes within the body. The ICG dye is injected into a patient and glows when exposed to near-infrared light. Specialized cameras detect this glow, allowing medical professionals to observe real-time physiological activity. The technique provides a dynamic view of how substances move through the body, aiding in various diagnoses and surgical procedures.
Understanding Indocyanine Green
Indocyanine green is a water-soluble, cyanine dye with unique optical properties suitable for medical imaging. When exposed to near-infrared (NIR) light, ICG absorbs and then re-emits it at a longer wavelength, a phenomenon known as fluorescence. Specialized cameras detect these NIR wavelengths to visualize the dye.
The dye is typically administered intravenously. Once in the bloodstream, ICG rapidly binds to plasma proteins, circulating throughout the body. Unlike some other dyes, ICG remains within blood vessels and does not leak into surrounding tissues, providing clear images of blood flow and vessel structures. The liver then quickly processes and excretes the dye, minimizing its presence in the body over time.
Key Medical Uses of ICG Imaging
ICG imaging has found widespread application across medical fields due to its ability to provide real-time visualization of various biological processes. One significant use is in assessing blood flow, also known as angiography. In ophthalmology, ICG angiography is used to visualize blood vessels in the retina and choroid, aiding in the diagnosis of conditions like age-related macular degeneration and central serous chorioretinopathy by providing clearer views of deeper, potentially leaky vessels.
Beyond ophthalmology, ICG evaluates tissue perfusion during reconstructive surgeries. Surgeons monitor the blood supply to tissue flaps and grafts, ensuring adequate vascularization for their survival, which enhances surgical precision and reduces complications. Similarly, in colorectal surgery, ICG fluorescence angiography is used intraoperatively to assess the perfusion of bowel segments before creating connections, known as anastomoses.
ICG imaging also identifies anatomical structures and delineates tumors. For instance, it helps surgeons visualize the biliary tract, including the cystic and common bile ducts, during laparoscopic cholecystectomy, reducing bile duct injury risk. In cancer surgery, ICG aids in visualizing tumor margins for more precise removal of malignant tissues while preserving healthy surrounding tissue, including applications in oral, liver, pancreas, and adrenal gland surgeries.
ICG is utilized for lymphatic mapping and sentinel lymph node biopsy, particularly in cancer staging for various malignancies such as breast, colon, rectum, esophagus, and skin cancer. By tracing the flow of ICG through the lymphatic system, surgeons can identify the first lymph nodes to which cancer cells are likely to spread, thereby improving the accuracy of staging and treatment planning.
Benefits and Safety Considerations
ICG imaging offers several advantages over other diagnostic methods, contributing to improved patient care and surgical outcomes. A benefit is its ability to provide real-time visualization of blood flow, tissue perfusion, and anatomical structures, which was often previously unavailable to surgeons. This immediate feedback allows for dynamic decision-making during procedures, potentially reducing complications and enhancing surgical precision. Moreover, ICG imaging uses non-ionizing near-infrared light, avoiding the radiation exposure associated with techniques like X-rays or CT scans.
The safety profile of indocyanine green is favorable, with a low incidence of adverse reactions. ICG has been approved for medical use since 1959 and has an established safety record worldwide. Common side effects are rare and mild, such as temporary changes in blood pressure or allergic reactions.
However, certain contraindications exist for ICG administration. Patients with a known allergy to iodine or indocyanine green itself should not receive the dye. Caution is also advised for individuals with severe liver or kidney dysfunction, as these organs are involved in the dye’s metabolism and excretion.