Assessment of Acetazolamide Reactivity in Cerebral Blood Flow Using Spectral Analysis and Technetium-99m Hexamethylpropylene Amine Oxime

Abstract

Cerebral blood flow (CBF) can be quantified noninvasively using the brain perfusion index (BPI), determined from radionuclide angiographic data generated with technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO). Previously, the BPI has been calculated using graphical analysis (GA); however, the GA method is greatly affected by the first-pass extraction fraction and retention fraction, which are not only variable, but lower in cases with an increased CBF, such as after the administration of acetazolamide. Thus, GA-calculated BPI values (BPIG) may not reflect the absolute CBF. The objective of this study was to use the spectral analysis of radionuclide angiographic data collected using 99mTc-HMPAO to examine changes in the BPI after the administration of acetazolamide. We studied the CBF of both cerebral hemispheres in six healthy male volunteers; the BPI was measured at rest and after the intravenous administration of 1 g of acetazolamide. In all participants, an H215O positron emission tomography (PET) examination was also performed, and the spectral analysis—calculated BPI values (BPIS) and BPIG values were compared with the actual CBF measured using H215O PET (mCBFPET). The BPIS was 1.070 ± 0.051 (mean ± SD) at rest and 1.497 ± 0.098 after acetazolamide; the corresponding BPIG values were 0.646 ± 0.073 and 0.721 ± 0.107. The BPIS values were significantly correlated with the mCBFPET values, whereas the BPIG values were not. According to the BPIS values, the increase in BPI after the intravenous administration of acetazolamide was 40.1 ± 8.4%, as opposed to an increase of only 11.3 ± 6.5% according to the BPIG values. These results suggest that the spectral analysis of 99mTc-HMPAO—generated data yields a more reliable BPI than GA for the quantification of CBF after acetazolamide administration.