[Comparison of cerebral vasoreactivity to acetazolamide in normal volunteer among 123I-IMP, 99mTc-ECD and 99mTc-HMPAO].

We studied the difference in the cerebral vasoreactivity to acetazolamide among three cerebral blood flow tracers, N-isopropyl-p-123I-iodoamphetamine (123I-IMP), 99mTc-ethyl cysteinate dimer (99mTc-ECD), 99mTc-hexamethylpropylene amine oxime (99mTc-HMPAO). Subjects were 4 healthy male adult volunteers at ages respectively of 30, 30, 35 and 41 years. Each subject underwent SPECT total 6 times. The three tracers were each used in the tests during rest and during acetazolamide loading, which were performed on different days. At least three days were allowed to intervene between one test and another, and all tests were completed within 2 months. The blood flow was calculated on the microsphere model with 123I-IMP, and Patlak plot method with 99mTc-ECD and 99mTc-HMPAO, to perform quantitative assessment. In the acetazolamide loading test, 1 g acetazolamide was intravenously administered, and each tracer was administered at 15 minutes after that. mCBF and BPI data on total 8 sides, one side representing the right or left side of each subject, were statistically analyzed. For rCBF, the region of interest was set up on the right and left sides of the frontal, temporal and occipital lobes on the slice passing through the third ventricle. The percent increase in mCBF with IMP was 29.3 +/- 10.5% (Mean +/- SD), significantly higher than 10.4 +/- 3.9% (p < 0.05) with ECD or 8.9 +/- 6.9% (p < 0.02) with HMPAO. The percent increase in rCBF with IMP was 30.8 +/- 13.4%, significantly higher than 14.3 +/- 13% (p < 0.001) with ECD or 8.7 +/- 14.8% (p < 0.001) with HMPAO. The percent increase in rCBF with ECD was higher than that with HMPAO, but not significantly. The percent increase in BPI calculated by Patlak plot method with ECD (26.4 +/- 14.3%) was higher than that with HMPAO (13.9 +/- 12.8%), but not significantly. It has been pointed out that 99mTc-ECD and 99mTc-HMPAO underestimate blood flow in the high blood flow area, which seemed to account for the underestimation of acetazolamide reactivity. The extent of underestimation in the high blood flow area is less with 99mTc-ECD than with 99mTc-HMPAO, while the stability of the preparation under acetazolamide is maintained, which seemed to explain difference in the reactivity.