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-effect lasted for approximately 45 minutes after administration. In patients with chronic occlusive cerebrovascular disease, signal changes on susceptibility-weighted MR images of occluded areas with normal vasodilatory capacity on SPECT images did not differ from signal changes of nonoc-clusive areas. In those patients with changes that reflected diminished vasodilatory capacity, the MR images showed a lower percentage of signal changes after acetazolamide administration than those in normally perfused areas. CONCLUSION: Susceptibility-weighted MR imaging offers an alternative method for estimating vasodilatory capacity. Index terms: Blood, magnetic resonance; Cerebral blood flow; Magnetic resonance, gradient-echo AJNR Am J Neuroradiol 17:631–637, April 1996 Recently, new techniques have been devel-oped for studying human brain function by us-ing magnetic resonance (MR) imaging tech-nology. One of these techniques exploits differences in the magnetic susceptibility of ox-ygenated and deoxygenated hemoglobin t