title: Usefulness of rate of increase in SPECT counts in one-day method of N-isopropyl-4-iodoamphetamine [123I] SPECT studies at rest and after acetazolamide challenge using a method for estimating time-dependent distribution at rest.
abstract: 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.
authors.affiliation: Department of Radiology, Jichi Medical University Hospital, 311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan. ykawamu@jichi.ac.jp
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Kawamura
authors.forename: Michio
authors.initials: M
authors.lastname: Ashizaki
authors.forename: Shoko
authors.initials: S
authors.lastname: Saida
authors.forename: Hideharu
authors.initials: H
authors.lastname: Sugimoto
mesh_terms: D000086:Acetazolamide / Q000008:administration & dosage; D000662:Amphetamines / Q000008:administration & dosage; D001921:Brain / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008657:Metabolic Clearance Rate / Q000187:drug effects; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012146:Rest; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D000662:Amphetamines; D019275:Radiopharmaceuticals; D014665:Vasodilator Agents; C041336:4-iodoamphetamine; D000086:Acetazolamide