99Tcm labeled C2A domain of synaptotagmin I (99Tcm-Syt I-C2A) is a scintigraphic tracer that binds to phosphatidylserine exposed on activated platelets. This study is to determine the potential of this agent for imaging acute venous thrombosis. A stainless steel was placed in femoral vein for inducing venous thrombi in 5 dogs

which were injected each with 185 MBq of 99Tcm-Syt I-C2A. Images of legs were acquired at 1

2 and 3 h after injection. ROI analysis was applied to measure the thrombus-to-contralateral location and thrombus-to-background ratios. The samples of thrombus

blood

and muscle were separated and were counted in a γ well counter for percent injected dose %ID·g-1. Thrombus-to-blood and thrombus-to-muscle ratios were calculated from the %ID·g-1 value. In in vivo imag- ing

the thrombus-to- contralateral location ratios were 3.01±0.30

3.22±0.21 and 3.37±0.57

respectively

and throm- bus-to-background ratios were 3.10±0.39

3.32±0.31 and 3.50±0.45

respectively

at 1

2 and 3 h after injection. The thrombus-to-blood and thrombus-to-muscle ratios of %ID·g-1 were 2.40±0.35 and 68.90±45.30

respectively. 99Tcm-Syt I- C2A with high venous thrombus uptake is a promising agent for imaging acute venous thrombosis.