A STUDY OF ACETAZOLAMIDE-INDUCED CHANGES IN CEREBRAL BLOOD-FLOW USINGTC-99M HMPAO SPECT IN PATIENTS WITH CEREBROVASCULAR-DISEASE

For semiquantification of SPECT studies we tried to calculate cerebral Tc-99m-HMPAO uptake related to injected dose and estimated brain volu me. The method was applied to SPECT investigations of 27 patients who had a least one ischaemic attack and a confirmed 80-100% stenosis of t he corresponding internal carotid artery (ICA). Vascular reactivity wa s tested by parenteral administration of acetazolamide (AZ). Increase in HMPAO uptake after AZ was evident in both hemispheres, although the increase (AZ effect) was significantly lower in the affected hemisphe re (+24% versus +28%). No interhemispheric uptake differences were see n in patients with largely normal SPECT studies, although local asymme tries in HMPAO deposition were visible. Patients with low density lesi ons on CT and with a well-demarcated lesion in the same location on SP ECT revealed interhemispheric uptake differences, with lower uptake on the affected side. This was not due solely to alterations in the lesi on, but also to reduced HMPAO uptake and AZ effect in the surrounding area. The AZ effect showed no correlation with angiographic findings, indicating no major haemodynamic influence of the ICA stenosis on cere bral hemisphere perfusion. Calculated cerebral HMPAO uptake changes af ter AZ administration were in good accordance with absolute cerebral b lood flow measurements, and made interindividual comparisons possible. However, as changes in the area around an infarct or local reduction in vascular reserve may not be reproduced adequately by uptake calcula tions, visual inspection is still necessary.