Comparison of In-111-labeled platelets and iodinated fibrinogen for the detection of deep vein thrombosis.

Indium-111-labeled platelets and I-125 fibrinogen were administered to dogs with experimentally induced deep-vein thrombosis. The thrombus uptake of both labeled compounds was studied as a function of thrombus age. In thrombi less than 24 hr old, thrombus-to-blood ratios for In-111 platelets were about twice as great as those obtained for I-125 fibrinogen. Excellent scintiphotos were obtained with In-111 platelets. In thrombi older than 24 hr, uptake of both agents was low, but good images were still obtained with In-111 platelets. The images in this case are not of thrombi, but rather of damaged vessel wall. Indium-111-labeled platelets are superior to iodinated fibrinogen for imaging fresh thrombi, but offer no advantage for thrombi over 24 hr old.