Arjen Lindenholz

29 Clinical Vascular Imaging in the Brain at 7T 2 Cortical microinfarcts Another major clinical advancement of 7T MRI is its ability to detect cortical microinfarcts (CMIs) ( Figure 4 ). Historically being a strictly pathologic diagnosis recorded during autopsy in elderly people, high resolution MRI has made it possible to visualize some of these lesions in vivo at 7T ( Figure 4 ) 46-49 and to a lesser degree at 3T. 1,50 Nevertheless, the majority of microinfarcts currently remain under the detection limits of clinical in vivo MRI. 51 On post-mortem 7T MRI studies, three types of CMIs have been distinguished based on the involvement of all three cortical layers (type 1), two cortical layers (type 2), or one (superficial, middle or deep) cortical layer only (type 3. 52 CMIs should be distinguished from enlarged or atypically shaped perivascular spaces, which can be CMI mimics but which are located juxtacortically ( Figure 5 ). 53 CMIs are associated with atherosclerosis, and are believed to be of microembolic origin. 54-56 Also, CMIs are a new marker of vascular dementia, especially if occurring in strategic locations, such as the inferior frontal and cingulate gyri. 50,52,57 Although CMIs have also been described in the cerebellum on post-mortem 7T MRI studies, the somewhat larger cortical infarct cavities ( < 1.5 cm) are more frequently observed in that region ( Figure 6 ). 58-60 As originally found on post-mortem 7T MRI, those cerebellar cortical infarct cavities demonstrate a characteristic sparing of juxtacortical white matter ( Figure 6 ), a finding which has recently allowed translation to lower field-strength MRI in vivo. 59,61 Like CMIs, cerebellar cortical infarct cavities are associated with atherosclerosis and believed to be of embolic origin. 30,33 Figure 4. Cortical microinfarcts. 7T contrast-enhanced 3D-FLAIR imaging of a 68-year-old man with a large right-sided temporoparietal ischemic infarction ( A ), repetition time 8000 ms, echo time 300 ms, inversion time 2200 ms, acquired voxel size 0.8 × 0.8 × 0.8 mm 3 , reconstructed voxel size 0.5 × 0.5 × 0.5 mm 3 , field-of-view 250 x 250 × 190 mm 3 , scan duration 10 minutes 48 seconds. ( A ) Sagittal and ( B ) axial reconstruction shows multiple tiny cortical hyperintensities, compatible with cortical microinfarcts. Most cortical microinfarcts seen involve all cortical layers, compatible with type I microinfarcts according to. 52