MR-Imaging in acute stroke: Results from the ImagingNet of the Competence Net Stroke

Im Rahmen multizentrischer Studien im Subnetz „Bildgebende Verfahren beim akuten Schlaganfall“ (ImagingNet) im Kompetenznetz Schlaganfall wurden wichtige Fragen zur Pathophysiologie der akuten zerebralen Ischämie und zum Stellenwert der MR-Bildgebung für Therapieentscheidungen beantwortet. Erstens kann man heute davon ausgehen, dass die Kernspintomographie (MRT) der Computertomographie im Nachweis akuter zerebraler Blutungen mindestens gleichwertig, bei der Darstellung chronischer „Mikrobleeds” aber überlegen ist. Zweitens hat sich die diffusionsgewichtete MRT (DW-MRT) als hoch sensitives Instrument in der sehr frühen Darstellung akuter zerebraler Ischämien erwiesen. Drittens bildet die Kombination aus DW-MRT und perfusionsgewichteter MRT (PW-MRT) ein zuverlässiges operationales Mismatch-Konzept zum Verständnis der Pathophysiologie der zerebralen Ischämie. Die Anwendung des Schlaganfall-MRT ist relevant für Therapieentscheidungen auch außerhalb des 3-Stundenfensters.Studies from the ImagingNet within the Competence Net Stroke were important steps towards acceptance of stroke MRI and understanding of pathophysiology of ischemic stroke. It could be shown that MRI is at least as good as CT in the detection of early acute cerebral hemorrhage, but it may be even better in the detection of “chronic microbleeds”. Secondly, diffusion-weighted MRI (DWI) is now proven highly sensitive in the detection of early ischemic infarction. Finally, the combination of DWI and perfusionweighted Imaging (PWI) givesa useful operational „mismatch”-definition and new insights into the pathophysiology of ischemic stroke which is relevant for therapeutic decisions outside the 3-hour-time-window for systemic thrombolysis

Vessel size imaging reveals pathological changes of microvessel density and size in acute ischemia

The aim of this study was to test the feasibility of vessel size imaging with precise evaluation of apparent diffusion coefficient and cerebral blood volume and to apply this novel technique in acute stroke patients within a pilot group to observe the microvascular responses in acute ischemic tissue. Microvessel density-related quantity Q and mean vessel size index (VSI) were assessed in 9 healthy volunteers and 13 acute stroke patients with vessel occlusion within 6 hours after symptom onset. Our results in healthy volunteers matched with general anatomical observations. Given the limitation of a small patient cohort, the median VSI in the ischemic area was higher than that in the mirrored region in the contralateral hemisphere (P<0.05). Decreased Q was observed in the ischemic region in 2 patients, whereas no obvious changes of Q were found in the remaining 11 patients. In a patient without recanalization, the VSI hyperintensity in the subcortical area matched well with the final infarct. These data reveal that different observations of microvascular response in the acute ischemic tissue seem to emerge and vessel size imaging may provide useful information for the definition of ischemic penumbra and have an impact on future therapeutic approaches

Divergent regional patterns of cerebral hypoperfusion and gray matter atrophy in mild cognitive impairment patients

Reductions of cerebral blood flow and gray matter structure have been implicated in early pathogenesis of Alzheimer’s disease, potentially providing complementary information. The present study evaluated regional patterns of cerebral hypoperfusion and atrophy in patients with mild cognitive impairment and healthy older adults. In each participant, cerebral perfusion and gray matter structure were extracted within selected brain regions vulnerable to Alzheimer’s disease using magnetic resonance imaging. Measures were compared between diagnostic groups with/without adjustment for covariates. In mild cognitive impairment patients, cerebral blood flow was significantly reduced in comparison with healthy controls in temporo-parietal regions and the basal ganglia in the absence of local gray matter atrophy. By contrast, gray matter structure was significantly reduced in the hippocampus in the absence of local hypoperfusion. Both, cerebral perfusion and gray matter structure were significantly reduced in the entorhinal and isthmus cingulate cortex in mild cognitive impairment patients compared with healthy older adults. Our results demonstrated partly divergent patterns of temporo-parietal hypoperfusion and medial-temporal atrophy in mild cognitive impairment patients, potentially indicating biomarker sensitivity to dissociable pathological mechanisms. The findings support applicability of cerebral perfusion and gray matter structure as complementary magnetic resonance imaging-based biomarkers in early Alzheimer’s disease detection, a hypothesis to be further evaluated in longitudinal studies