Noninvasive quantification of microvascular density in carotid atherosclerotic plaques using mri with paramagnetic contrast enhancement

Aim. We have carried out the direct comparison between MR-images of atherosclerotic plaques of carotid arteries and morphologic density of microvasculature of the plaques, as seen from surgical specimen removed at carotid endarterectomy. Materials and Methods. Twenty two patients with internal carotid artery stenosis over 70% were included and all underwent contrast-enhanced MRI and MR-angiography of carotid arteries before carotid endarterectomy. In order to quantify the changes in T1-weighted images due to contrast uptake to the plaque, the index of enhancement (IE) was calculated in all patients as ratio of post- and pre-contrast intensities per voxel over the plaque. The index of vascularity was scored from the microscopy of the resected specimen based on the number of capillaries in plaque per field of view (f.o.v) (mag.x200). In particular: 0 - no capillaries detected; 1 degree - 1-3 /f.o.v; 2 - 4-6 /f.o.v; 3 - 7-9 /f.o.v; 4 - 10 or more. Results. Vascularity degree 0-1 was observed when IE was in ranges of 1.01-1.15; degree 2 corresponded to IE of 1.16-1.34; degree 3 corresponded to IE of 1.35-1.46; vascularity degree 4 corresponded to IE >1.46. In all cases, the inter-group significance of differences was p1.22. Conclusions. Enhanced uptake of paramagnetic contrast agent to the atherosclerotic plaque occurs when the capillary vascularity of the plaque is enhanced and when revealed (i.e. if index of enhancement is over 1.22) should be accepted as additional indication to carotid endarterectomy or to stenting of the stenosis. The quantitative processing of the contract-enhanced MRI of the carotid plaques and arterial walls of the carotid arteries should be employed for noninvasive evaluation of the vascularity of atherosclerotic lesions.