Magnetic Resonance Perfusion-Weighted Imaging of Acute Cerebral Infarction

Abstract

Background and Purpose-Various calculation methods are available to estimate the transit-time on MR perfusionweighted imaging (PWI). Each method may affect the results of PWI. Steno-occlusive disease in the parent vessels is another factor that may affect the results of the PWI. The purpose of this study was to elucidate the effect of the calculation methods and underlying vasculopathy on PWI. Methods-From a pool of 113 patients who had undergone PWI during the study period, a total of 12 patients with nonlacunar ischemic strokes who were scanned within 24 hours after onset of symptom were selected for the study. The patient population consisted of 6 patients who had extracranial internal carotid artery stenosis (Ͼ70%) and 6 individuals without stenosis. Seven different postprocessing methods were evaluated: first moment, ratio of area to peak, time to peak (TTP), relative TTP, arrival time, full-width at half-maximum, and deconvolution methods. Follow-up MR or CT images were used to determine the areas that evolved into infarcts, which served as the gold standard. Sensitivity and specificity of each transit time technique were calculated. Results-Calculation methods with high sensitivity were the first moment (sensitivity, 74%), TTP (sensitivity, 77%), and deconvolution methods (sensitivity, 81% to 94%). Between the 2 groups with and without internal carotid artery stenosis, the specificity of most of the techniques was lower in the internal carotid artery stenosis group. The first moment and deconvolution methods maintained relatively high specificity even in the stenosis group. Conclusions-The calculation technique and presence of underlying vasculopathy have a direct impact on the results of PWI. The methods with high sensitivity even in the presence of steno-occlusive disease were the first moment and deconvolution methods with arterial input function derived from the peri-infarct arteries; the deconvolution method was the superior choice because of higher lesion conspicuity.

The Performance of MRI-Based Cerebral Blood Flow Measurements in Acute and Subacute Stroke Compared With 15O-Water Positron Emission Tomography

“…According to previous studies of TTP maps in patients with high-grade ICA stenosis, vessel pathology was supposed to influence the reliability of PWI maps. 37,50 However, we found the performance of CBF MRI not related to the presence of extracranial vessel pathology because an ipsilateral stenosis or occlusion did not significantly change the C-ratio. This discrepancy to the previous studies can be explained by the fact that CBF maps are less sensitive to collateral flow than TTP maps.…”

“…This discrepancy to the previous studies can be explained by the fact that CBF maps are less sensitive to collateral flow than TTP maps. 50,51 The finding that the few patients with contralateral ICA pathology (nϭ4) did not differ in their performance of CBF MRI is of considerable interest but should be clarified in larger patient samples. Taken into account our sample size and the resulting subgroups of vessel pathology, these results suggest that the AIF-based CBF measurement seems mainly independent of ipsilateral vessel pathology.…”

“…44 These findings differ from studies of acute ischemia in which AIF selection does affect quantitative parameters. 37,50 A manually chosen AIF is highly observer dependent, whereas automatic algorithms could be helpful but are not fully validated yet. 55 We therefore constantly derived the AIF from intravascular voxels 33 of the first 2 segments of the MCA or from the distal ICA of the unaffected hemisphere.…”

Principles of cerebral perfusion imaging by bolus tracking

“…Although the dependence of these indices on MTT and CBF depends strongly on the vascular structure and the AIF (41), these indices often suffice to delineate pathological changes and provide important qualitative information in many diseases. It appears, however, that the derivation of CBF, CBV, and MTT from kinetic principles somewhat improves specificity and sensitivity of clinical studies, facilitating inter-and intrasubject comparisons (48).…”

Crossed Cerebellar Diaschisis: Insights into Oxygen Challenge MRI

“…Yamada et al 13 showed reduced CBV in the contralesional hemisphere in 10 subacute stroke subjects. In a back-to-back PET-MR study, Madai et al 6 reported mild cerebellar asymmetry on MRP maps measuring CBF and CBV, with normal time to peak.…”