Indocyanine green (ICG) fluorescence is a medical imaging technique that utilizes a special dye to visualize internal body structures. This method allows medical professionals to observe processes like blood flow or tissue perfusion in real-time. By introducing this dye into the body and exciting it with specific light, it emits a glow that specialized cameras can detect. This allows for enhanced visibility during various diagnostic and surgical procedures.
Understanding Indocyanine Green
Indocyanine green (ICG) is a water-soluble dye that has been used in medicine for over six decades, first approved by the FDA in 1959. It is an amphiphilic, tricarbocyanine compound with a mass of 751.4 Da, designed for intravenous injection. Its rapid binding to plasma proteins, primarily albumin, keeps the dye within the vascular system and contributes to its non-toxic profile.
ICG’s unique optical properties make it suitable for medical imaging. When exposed to near-infrared (NIR) light, typically around 780-800 nm, ICG absorbs this energy and becomes excited. As the dye returns to its stable state, it emits light at a slightly longer wavelength, usually around 830-835 nm, a phenomenon known as fluorescence. This emitted NIR light penetrates tissues and is captured by specialized cameras, allowing real-time visualization where the dye accumulates.
Medical Applications
ICG fluorescence imaging has significantly expanded its utility across numerous medical specialties, providing enhanced visualization for various diagnostic and surgical procedures. Its ability to show real-time information makes it a valuable tool in diverse clinical scenarios.
Angiography is a primary application, where ICG visualizes blood flow dynamics. In ophthalmology, retinal angiography uses ICG to assess blood circulation in the choroid, a layer of blood vessels behind the retina, aiding in the diagnosis of certain eye conditions. Similarly, cerebral angiography can employ ICG to evaluate blood flow in the brain, assisting neurosurgical planning and vascular integrity assessment. It also aids cardiac output assessment by tracking dye circulation through the heart.
ICG fluorescence is widely used for sentinel lymph node mapping, a procedure to identify the first lymph nodes to which cancer cells are most likely to spread. This technique is particularly beneficial in cancers like breast cancer and melanoma, where precise identification of these nodes guides surgical decisions regarding lymph node dissection. ICG offers advantages over traditional methods like technetium-99 and methylene blue, providing more accurate detection of deeper lymphatic structures and avoiding radiation.
During surgical procedures, ICG fluorescence serves as a powerful guidance tool for surgeons. It allows for real-time visualization of anatomical structures that might be difficult to see with the naked eye or under normal white light. For instance, in gastrointestinal surgery, ICG can assess tissue perfusion at anastomotic sites, which are areas where two parts of the intestine are joined, helping to reduce complications like anastomotic leakage. In plastic surgery, it helps evaluate tissue viability and blood supply in flaps used for reconstruction.
Neurosurgeons utilize ICG for visualizing blood vessels during brain tumor removal and other complex cranial procedures. ICG also identifies ureters during complex pelvic surgeries, helping prevent accidental injury.
Beyond these uses, ICG is employed for general perfusion assessment, evaluating the blood supply to various tissues and organs. This is particularly useful in situations where tissue viability needs to be confirmed, such as in organ transplantation or reconstructive surgery. The real-time feedback provided by ICG fluorescence allows surgeons to make immediate, informed decisions during procedures, ultimately aiming to improve patient outcomes.
Safety Profile and Administration
Indocyanine green has a favorable safety profile, making it a widely accepted agent in various medical procedures. Adverse reactions are infrequent and typically mild. These include minor symptoms like nausea, itching, or a temporary feeling of warmth.
Severe reactions, such as anaphylaxis, are rare, occurring in approximately 1 in 42,000 administrations. Due to its iodine content, ICG is contraindicated in patients with an iodine allergy. Individuals with severe liver disease may also be advised against ICG use, as the liver primarily excretes the dye.
ICG is administered intravenously, injected directly into a vein. Dosage varies by application and patient weight, generally ranging from 0.1 to 0.5 mg/kg. After injection, the dye rapidly circulates, binding to plasma proteins. Its swift excretion by the liver ensures it is cleared from the body quickly, usually within minutes to a few hours, minimizing prolonged systemic exposure.