In vivo noninvasive detection and age definition of arterial thrombus by MRI

OBJECTIVES The purpose of this study was to evaluate the potential of magnetic resonance (MR) to detect arterial thrombotic obstruction and define thrombus age. BACKGROUND Arterial thrombi underlie the clinical consequences of atherosclerosis and are not reliably detected by current noninvasive diagnostic techniques, METHODS Carotid thrombi were induced in swine (n = 7) by arterial injury. Serial high-resolution in vivo AIR images were obtained using black-blood Tl-weighted (T1W) and T2-weighted (T2W) sequences in a clinical 1.5T MR system at 6 h, 1 day and at 1, 2,3, 6 and 9 weeks. At each time point one animal was sacrificed and the occluded carotid artery processed for histopathology. Thrombus signal intensity (SI) was normalized to that of the a adjacent muscle, Thrombus age was assessed based on MR appearance by two blinded independent observers. RESULTS Thrombus appearance and relative SI revealed characteristic temporal changes in multicontrast-weighted MR images, reflecting histologic changes in the composition, Acute thrombus appeared very bright on the T2 V images, facilitating the detection. Signal intensity was 197 +/- 25% at 6 h, peaking at 1 week (246 +/- 51%), reaching a plateau by 6 weeks (120 15916). At six weeks, complete thrombus organization was confirmed histologically. The T1W images had similar pattern with lower SI than T2W. Age definition using visual appearance was highly accurate (Pearson's chi-square with 4 df ranging from 96 to 132 and Cohen's kappa at 0.81 to 0.94). Agreement between observers was substantial (Pearson's chi-square with 4 df = 91.5, kappa = 0.79). CONCLUSIONS Magnetic resonance imaging is a promising tool to noninvasively detect arterial thrombosis, Measurement of SI and the characteristic visual appearance of the thrombus have potential to define thrombus age. (J Am Coll Cardiol 2002;39:1306-73) (C) 2002 by the American College of Cardiology Foundation.