Arjen Lindenholz

26 CHAPTER 2 wall changes on 3T and 7T and brain infarction have been published. 12-14 Although most studies have so far only been performed in a limited number of patients, the following preliminary conclusions may be drawn. Eccentric atherosclerotic lesions are most frequently detected and seem to be associated with a focal (short-segment) thickening pattern, while concentric plaques usually show a more diffuse (long-segment) thickening. 14 Although contrast-enhancement of intracranial atherosclerotic plaques is frequently observed and has been linked to the vessels supplying the area of ischemic injury, it may as well appear in asymptomatic lesions. 10,14-16 Since atherosclerotic lesions of the intracranial vasculature cannot be correlated with histopathology in living patients (unlike the carotid plaques, which may be surgically removed by endarterectomy), only post- mortem quantitative MRI-pathologic correlation studies have been performed to compare plaque contents with plaque signal intensities on 3T and 7T on CoW. 17-20 These have shown the promising result that different tissue components of advanced intracranial plaques have distinguishable relaxation times on ultra-high- resolution quantitative MR imaging. T2 and T2* relaxation times at 3T, and T1 relaxation times at 7T, have shown the most differences among individual tissue components of intracranial plaques, including lipid, fibrous tissue, fibrous cap, calcifications, and the healthy vessel wall. 17,18 Hence, the most promising method for distinguishing intracranial plaque components at 7T is T1-weighted imaging. Figure 2 . MR Angiography of the intracranial perforating arteries. Coronal Maximum Intensity Projection (MIP) of a 7T Time-of-Flight (TOF) MRA, repetition time 16 ms, echo time 3.3 ms, acquired voxel size 0.25 × 0.3 × 0.4 mm 3 , reconstructed voxel size 0.2 × 0.2 × 0.2 mm 3 , field-of-view 200 x 190 × 50 mm 3 , scan duration 9 minutes 54 seconds, performed in a 51-year-old male. Perforating lenticulostriate arteries (arrowheads) branching off from the middle cerebral arteries are clearly seen in both cerebral hemispheres.