title: Regional differences in technetium-99m-ECD clearance on brain SPECT in healthy subjects.
abstract: The aim of this study was to evaluate the in vivo stability of ECD brain SPECT.
  
  
  METHODS
  Twenty normal volunteers (35.4 +/- 9.1 yr) each had six ECD scans at 30, 60, 120, 240, 360 and 480 min postinjection. Each scan was acquired for 24 min using a triple-head SPECT system. Average counts per pixel were measured from frontal, temporal, parietal, occipital, cerebellum, basal ganglia, thalamus and white matter regions. ECD clearance rates were calculated by fitting regional time activity data to a monoexponential equation. Regional gray-to-white matter (G/W) and gray-to-cerebellum (G/C) ratios were calculated for each scan. Analysis of variance was used to compare regional ECD clearance and ratio measurements.
  
  
  RESULTS
  The average ECD clearance was 4.3%/hr. There was a significant regional variation in the ECD clearance, being higher for occipital (6.34%/hr) but lower for both white matter (2.39%/hr) and thalamus (2.45%/hr). Both G/W and G/C ratios showed a significant regional variation with time. The overall G/W ratio was 2.13 at 30 min and became progressively lower after 2 hr, reaching 1.78 at 8 hr. All regional G/W ratios declined with time except for thalamus where it remained constant at 2.15. The overall G/C ratio was 0.984 at 30 min but it declined after 4 hr, reaching 0.955 at 8 hr. All regional G/C ratios declined with time except for thalamus where it increased progressively from 0.955 to 1.120 at 8 hr.
  
  
  CONCLUSIONS
  ECD clears from normal brain slowly and shows a significant regional variation. As a result, G/W contrast begins to decrease after 2 hr and the gray-matter activity pattern becomes significantly different after 4 hr. Therefore, the optimal imaging time may be between 30-120 min. However, images obtained up to 4 hr still maintain the initial gray-matter activity pattern.
authors.affiliation: Department of Nuclear Medicine, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Ichise
authors.forename: H
authors.initials: H
authors.lastname: Golan
authors.forename: J R
authors.initials: JR
authors.lastname: Ballinger
authors.forename: D
authors.initials: D
authors.lastname: Vines
authors.forename: A
authors.initials: A
authors.lastname: Blackman
authors.forename: H
authors.initials: H
authors.lastname: Moldofsky
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000502:physiology; D003545:Cysteine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D008297:Male; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C059659:technetium Tc 99m bicisate; D003545:Cysteine