Arjen Lindenholz

31 Clinical Vascular Imaging in the Brain at 7T 2 Microbleeds Detection of microbleeds may be of potential clinical relevance for a variety of pathologies, including brain trauma, hypertensive microangiopathy, cerebral amyloid angiopathy (CAA) and Alzheimer’s dementia (AD). 37,62-67 A recent post- mortem study has shown a strong association between cerebral microbleeds and CMIs in CAA, suggesting a shared underlying pathophysiologic mechanism. 68 Susceptibility effects and the sensitivity of T2* and SWI for detecting microbleeds increase with field strength, and 3D dual-echo T2*-weighted imaging at 7T has been found to result in better and more reliable detection of microbleeds compared with 3D T2*-weighted imaging at 1.5T in vivo. 69 Interestingly, a recent combined in-vivo/post-mortemMRI correlation study has shown that microbleeds on in vivo MRI are specific for microhemorrhages in CAA, but that increasing the resolution of magnetic resonance images with ultra-high resolution post mortem 7T MRI ( < 100 μ m isotropic voxels) results in the detection of more ‘non- hemorrhagic’ pathology. 51 In addition, diagnostic confidence of rating microbleeds in vivo has not been found significantly higher at 7T compared to 3T for the diagnosis and exclusion of microbleeds and vascular malformations. 70 Visual rating of microbleeds is more challenging at 7T than at lower field strengths due to the increased susceptibility effects of adjacent structures, such as veins. 71,72 Because manual detection of microbleeds may be time consuming with observer variability, automated detection systems of microbleeds have been developed. 73-75 Aneurysms, arteriovenous malformations and cavernomas Cerebral aneurysms 7T MRI has also been proven beneficial for the depiction of cerebral aneurysms, with overall image quality equaling the gold standard DSA. 76 7T has already proven its superiority over 1.5T in the analysis of aneurysm neck and dome, as well as in the evaluation of aneurysm location at the parent vessel. 77 Using 7T TOF-MRA, microaneurysms with diameters under 1 mm are now being described, e.g. ventricular microaneurysms in patients with moyamoya disease. 78 7T MPRAGE has been found superior to 7T TOF-MRA for the assessment of aneurysm features, with less artifacts and simultaneous high quality assessment of the brain with full coverage. 77 Interestingly, high-resolution vessel wall imaging has shown a strong association between ruptured aneurysms and circumferential aneurysm wall enhancement in subarachnoid hemorrhage (SAH), which may identify the site of rupture in patients with multiple intracranial aneurysms. 79-82 In addition, circumferential wall enhancement has been more frequently observed in unruptured but unstable (growing and symptomatic) aneurysms. 80,81 Although a minority of incidentally discovered aneurysms also show wall enhancement, it still needs to be established if these are at an increased risk of rupture. 80 Apart