Decreased Signal Intensity Ratio on MRA Reflects Misery Perfusion on SPECT in Patients with Intracranial Stenosis

ABSTRACT BACKGROUND AND PURPOSE Acetazolamide reactivity on 123 I‐IMP SPECT is used to detect misery perfusion due to intracranial atherosclerosis. Noninvasive fractional flow assessed by signal intensity ratio (SIR) on time of flight‐magnetic resonance angiography (TOF‐MRA) might offer a feasible alternative to identify high‐risk intracranial stenosis. METHODS Data from consecutive patients with unilateral middle cerebral artery (MCA) stenosis who underwent both TOF‐MRA and acetazolamide reactivity on 123 I‐IMP SPECT were retrospectively analyzed. Signal intensity was measured in the background and on the MCA proximal and distal to the stenotic lesion on TOF‐MRA. Mean cerebral blood flow (CBF) at rest and cerebrovascular reactivity were measured in the target MCA territory. CBF patterns of the MCA were divided into three groups (Powers’ stage 0‐II). RESULTS A total of 56 sets of diagnostic imaging in 33 patients were assessed. Four CBF patterns were stage II in four MCA territories, stage I in 31, and stage 0 in 21. Median SIR of the MCA was .53 (interquartile range .46‐.69) for stage II, .78 (.63‐.90) for stage I, and .91 (.85‐.95) for stage 0. The optimal cutoff for SIR obtained from receiver operating characteristic curve analysis to predict stage II was < .56. CONCLUSIONS In patients with unilateral MCA stenosis, decreased SIR was correlated with misery perfusion, providing a simpler, widely available predictor of high‐risk intracranial stenosis.