Objective: When N-isopropyl-4-iodoamphetamine ((123)I-IMP) single-photon emission computed tomography (SPECT) studies at rest and after acetazolamide (ACZ) challenge are conducted in a day, the time-dependent change in IMP in the brain at rest should be estimated accurately. We devised the method and investigated whether our one-day method for measuring the rate of increase in SPECT counts allowed reduction in the acquisition time.
Methods: Sequential, 5-min SPECT scans were performed. We estimated the time-dependent change in the brain using the change in slopes of two linear equations derived from the first three SPECT counts. For the one-day method, ACZ was administered 15 min or 20 min after IMP administration. The second IMP was administered 10 min after ACZ administration.
Results: Time-dependent changes in the brain were classified into 13 patterns when estimation was started at 5 min after IMP administration and 6 patterns when estimation was started at 10 min, and fitting coefficients were determined. The correlation between actual measurements at 37.5 min and estimates was high with a correlation coefficient of 0.99 or greater. Rates of increase obtained from 20-min data were highly correlated with those obtained from 15-min or 10-min data (r = 0.97 or greater). In patients with unilateral cerebrovascular disease, the rate of increase on the unaffected side was 44.4 +/- 10.9% when ACZ was administered 15 min later and 48.0 +/- 16.0% when ACZ was administered 20 min later, and the rates of increase with different timings of administration were not significantly different.
Conclusions: The examination time may be reduced from 50 min to 45 min or 40 min as needed. The rate of increase was not influenced by the time frame for determination or the timing of ACZ administration. These findings suggest that our estimation method is accurate and versatile.