A 48-year-old-woman suffering from recurrent left hemipalsy was referred to the hospital. MRI showed hyperintense lesions in periventricular white matter. Cerebral angiography revealed stenosis in the bilateral internal carotid and hypertrophic collateral vessels at the brain base, compatible with moyamoya syndrome. A visual comparison between perfusion SPECT with and without acetazolamide is employed in evaluation of these patients. Nevertheless, this traditional evaluation has some drawbacks associated with the variability between the 2 SPECT images and the lack of anatomical information. We propose a quantitative method based on the realigment, normalization, substraction, and co-registration of the 2 perfusion SPECT with MRI.