Regional cerebral blood flow single-photon emission tomography with (TC)-T-99m-HMPAO and the acetazolamide test in the evaluation of vascular and Alzheimer's dementia

The diagnostic potential of technetium-99m hexamethylpropylene amine oxime (HMPAO) following systemic administration of the cerebral vasodilator aceta zolamide (acetazolamide test) was evaluated by regional cerebral blood flow (rCBF) single-photon emission tomography (SPET) in patients with Alzheimer 's disease (AD) or vascular dementia (VD). An initial, high-resolution SPET study was performed with Tc-99m-HMPAO, and after 2 days the patients were re-evaluated with Tc-99m-HMPAO following systemic administration of ac etaz olamide. Reconstructed SPET slices were evaluated visually and semiquantita tively by a semi-automatic rCBF map method. When Tc-99m-HMPAO alone was use d, bilateral hypoperfusion was found in the temporal and/or parietal region s in 33% (6/18) of the VD patients and in 70% (23/33) of the AD patients. T he corresponding data obtained by quantitative evaluation were 41% (7/17) a nd 71% (15/21), respectively. The vascular reserve capacity, as determined with the acetazolamide test, was preserved visually in 22% (4/18) and quant itatively in 29% (5/17) of the VD patients, but in 73% (24/33) and 76% (16/ 21) of the AD patients. The differences in the perfusion patterns between t he VD and AD patients were statistically significant (P < 0.01, Fischer's e xact test). Of the VD patients with hypoperfusion (bilateral temporal and/o r parietal), 4/6 (67%, visual evaluation) and 4/7 (57%, quantitative evalua tion) had a decreased vascular reserve capacity as determined with the acet azolamide test. In the AD group of patients the corresponding results were 3/23 (13%) and 4/15 (27%). It is concluded that the acetazolamide test is p romising in rCBF SPET to differentiate VD from AD.