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Abstract
BackgroundNeuroimaging may guide acute stroke treatment by measuring the volume of brain tissue in the irreversibly injured “ischemic core.” The most widely accepted core volume measurement technique is diffusion-weighted MRI (DWI). However, some claim that measuring regional cerebral blood flow (CBF) with CT perfusion imaging (CTP), and labeling tissue below some threshold as the core, provides equivalent estimates. We tested whether any threshold allows reliable substitution of CBF for DWI.Methods58 patients with suspected stroke underwent DWI and CTP within six hours of symptom onset. A neuroradiologist outlined DWI lesions. In CBF maps, core pixels were defined by thresholds ranging from 0%-100% of normal, in 1% increments. Replicating prior studies, we used receiver operating characteristic (ROC) curves to select thresholds that optimized sensitivity and specificity in predicting DWI-positive pixels, first using only pixels on the side of the brain where infarction was clinically suspected (“unilateral” method), then including both sides (“bilateral”). We quantified each method and threshold’s accuracy in estimating DWI volumes, using sums of squared errors (SSE). For the 23 patients with follow-up studies, we assessed whether CBF-derived volumes inaccurately exceeded follow-up infarct volumes.ResultsThe areas under the ROC curves were 0.89 (unilateral) and 0.90 (bilateral). Various metrics selected optimum CBF thresholds ranging from 29%-32%, with sensitivities of 0.79–0.81, and specificities of 0.83–0.85. However, for the unilateral and bilateral methods respectively, volume estimates derived from all CBF thresholds above 28% and 22% were less accurate than disregarding imaging and presuming every patient’s core volume to be zero. The unilateral method with a 30% threshold, which recent clinical trials have employed, produced a mean core overestimation of 65 mL (range: –82–191), and exceeded follow-up volumes for 83% of patients, by up to 191 mL.ConclusionCTP-derived CBF maps cannot substitute for DWI in measuring the ischemic core.
Highlights
Cerebral blood flow maps cannot substitute for diffusion-weighted MRI (DWI) in measuring the ischemic core share de-identified data with interested scientific researchers, upon request, and to share deidentified subject to any limitations that may be imposed by our IRB
computed tomography (CT) perfusion imaging (CTP)-derived cerebral blood flow (CBF) maps cannot substitute for DWI in measuring the ischemic core
Treatment of acute ischemic stroke patients may be guided by imaging-based estimation of the volume of brain tissue that has already suffered irreversible ischemic injury at the time of presentation, which is known as the ischemic “core.” Because the potential benefits of any acute stroke therapy are limited in patients who present with large cores,[1, 2] interventions that are risky or of uncertain efficacy may be best avoided in these patients
Summary
Treatment of acute ischemic stroke patients may be guided by imaging-based estimation of the volume of brain tissue that has already suffered irreversible ischemic injury at the time of presentation, which is known as the ischemic “core.” Because the potential benefits of any acute stroke therapy are limited in patients who present with large cores,[1, 2] interventions that are risky or of uncertain efficacy may be best avoided in these patients. [6] many hospitals lack continuous access to an MRI scanner that is available emergently for acute stroke patients.[7] researchers have searched for a technique that can obviate the need for DWI, by instead measuring the ischemic core’s volume with more widely available x-ray computed tomography (CT) scanners. One proposed method for doing this is the Alberta Stroke Programme Early Computed Tomography Score (ASPECTS), which was created in order to provide rough approximations of the extent of early ischemic signs in middle cerebral artery stroke patients’ noncontrast CT (NCCT) images.[8] Volumes of affected tissue cannot be measured reliably in NCCT images, because early ischemic signs are often visible only at gray matter-white matter interfaces. The most widely accepted core volume measurement technique is diffusion-weighted MRI (DWI). We tested whether any threshold allows reliable substitution of CBF for DWI
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