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

<bold>Background and Purpose: </bold>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.<bold>Methods: </bold>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).<bold>Results: </bold>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.<bold>Conclusions: </bold>In patients with unilateral MCA stenosis, decreased SIR was correlated with misery perfusion, providing a simpler, widely available predictor of high-risk intracranial stenosis. [ABSTRACT FROM AUTHOR]