Nearly a decade has passed since the introduction of 125I-fibrinogen as a tracer to aid in the clinical diagnosis of thrombosis. During this time many new radiopharmaceuticals have been developed for the detection of thrombi. Most of these have been designed to overcome the primary disadvantages of 125I-fibrinogen for uptake tests, namely, that it is limited to evaluation of the extremities, and it does not provide a scintigraphic image. Iodine-125-fibrinogen is now commercially available in the United States. We, therefore, concentrated our review on agents labeled with short-lived gamma-emitting nuclides useful for scintigraphy: 123I, 111In, 77Br, and 99mTc. In addition to being tagged with a variety of short-lived isotopes, fibrinogen has been chemically modified by overiodination and by clot formation/dissolution in attempts to accelerate its biologic clearance. These modifications have resulted in higher thrombus: blood ratios measured at earlier times when the photon flux is still high. Labeled leukocytes and platelets also have been tested as thrombus-localizing agents, and several components of the fibrinolytic system, including plasminogen, streptokinase, and urokinase, have been purified and labeled with iodine and/or technetium. The later agents could prove particularly useful for localizing older thrombi in which net fibrin deposition has slowed. Among the radiopharmaceuticals described for thrombus scintigraphy, chemically modified and fast clearing 123I-fibrinogen, 111In-platelets, and 123I-plasminogen show the greatest potential and should find extensive clinical application in the immediate future.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging