Background-Matrix metalloproteinase (MMP) activation plays a key role in vascular remodeling. RP782 is a novel indium 111 In-labeled tracer with specificity for activated MMPs. We hypothesized that RP782 can detect injury-induced vascular remodeling in vivo. Methods and Results-Left common carotid artery injury was induced with a guidewire in apolipoprotein E Ϫ/Ϫ mice. Sham surgery was performed on the contralateral artery, which served as control for imaging experiments. Carotid wire injury led to significant hyperplasia and expansive remodeling over a period of 4 weeks. MMP activity, detected by in situ zymography, increased in response to injury and was maximal by 3 to 4 weeks after injury. RP782 (11.1 MBq) was injected intravenously into apolipoprotein E Ϫ/Ϫ mice at 1, 2, 3, and 4 weeks after left carotid injury. MicroSPECT imaging was performed at 2 hours and was followed by CT angiography to localize the carotid arteries. In vivo images revealed focal uptake of RP782 in the injured carotid artery at 2, 3, and 4 weeks. Increased tracer uptake in the injured artery was confirmed by quantitative autoradiography. Pretreatment with 50-fold excess nonlabeled tracer significantly reduced RP782 uptake in injured carotids, thus demonstrating uptake specificity. Weekly changes in the vessel-wall area closely paralleled and correlated with RP782 uptake (Spearman rϭ0.95, Pϭ0.001

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