Aging of Acute Deep Vein Thrombosis Measured by Radiolabeled 99mTc-rt-PA

In previous studies, 99mTc-recombinant tissue plasminogen acti-vator (rt-PA) imaging has had a high sensitivity and specificity for the detection of deep vein thrombosis (DVT). In this technique, the plasminogen activation site of rt-PA undergoes inactivation but fibrin binding is retained. Uptake of 99mTc-rt-PA into DVT relies on binding of C-terminal lysine residues on fibrin. It is pos-tulated that as the thrombus ages, fewer fibrin sites are available for 99mTc-rt-PA and that there should be a progressive decrease in 99mTc-rt-PA uptake in old thrombi as compared with fresh thrombi. The ability to differentiate fresh from old thrombus would have significant clinical implications in the objective diagnosis of recurrent DVT. Our aim was to examine the relative uptake of 99mTc-rt-PA in acute DVT over the first 30 d after diagnosis. Methods: Seventy-four patients with acute symptomatic DVT were entered into the study. Patients underwent ultrasound and 99mTc-rt-PA imaging on days 1, 7, and 30.Results:Residual thrombuswas detected by ultrasonography in 46 (84%) of 55 pa-tients on day 7 and in 29 (66%) of 44 patients on day 30. Of the persisting thrombi on day 7, 72 % (33/46) showed 99mTc-rt-PA uptake. Of the persisting thrombi on day 30, 0 % (0/29) showed 99mTc-rt-PA uptake. Conclusion: Uptake of 99mTc-rt-PA into DVT was absent 30 d after diagnosis. This finding suggests that this imaging technique can distinguish fresh from old throm-bus