title: Comparison of technetium-99m-HMPAO and xenon-133 measurements of regional cerebral blood flow by SPECT.
abstract: This study compares 99mTc-HMPAO count ratios and derived regional cerebral blood flow (rCBF) to 133Xe rCBF ratios and true rCBF (ml/min/100 g), respectively.
  
  
  METHODS
  Technetium-99m-HMPAO distribution was evaluated in 14 patients and 5 normal control subjects. Immediately after 133Xe SPECT, subjects received 22 +/- 4mCi 99mTc-HMPAO, and images were acquired 15 min after injection. rCBF (ml/min/100 g, 133Xe) or regional count density (99mTc-HMPAO) were extracted from 24 ROI located 6 cm above the cantho-meatal line. These data were also normalized to global cerebral blood flow (gCBF) for 133Xe or to global count density (gCD) for 99mTc-HMPAO. Technetium-99m-HMPAO ROI data also were expressed in units of ml/min/100 g by relating gCD to gCBF. Comparisons between 133Xe and 99mTc-HMPAO were evaluated using a Bonferroni-corrected paired t-test and by linear regression analysis.
  
  
  RESULTS
  Profile plots demonstrated agreement in the pattern of relative distribution between rCBF ratios (133Xe) and count density ratios (99mTc-HMPAO). Regression analysis indicated a significant correlation (r = 0.78), with a modest slope (0.52) and a large intercept (0.48). A closer correlation (r = 0.92) was found for the comparison between rCBF (133Xe) and derived 99mTc-HMPAO rCBF. The slope was closer to one (0.82) and the intercept closer to zero. This relationship was also examined during high rCBF after a subset of these subjects (n = 7) was injected intravenously with 1 g acetazolamide. Again, profile plots and regression analysis demonstrated agreement in the pattern of distribution (ratios) between 133Xe and 99mTc-HMPAO (r = 0.66). However, the slope was reduced and the intercept increased relative to resting data. Absolute flow correlations showed some improvement relative to the ratio data (r = 0.77).
  
  
  CONCLUSIONS
  The distribution of 99mTc-HMPAO is linearly related to rCBF measured by 133Xe SPECT, although our data suggest that 99mTc-HMPAO mildly underestimates rCBF above 80 ml/min/100 g. These results are similar to our previous comparison of 99mTc-ECD and 133Xe.
authors.affiliation: Nuclear Medicine Center, University of Texas Southwestern Medical Center, Dallas 75235-9061, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Payne
authors.forename: M H
authors.initials: MH
authors.lastname: Trivedi
authors.forename: M D
authors.initials: MD
authors.lastname: Devous
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D008297:Male; D015609:Organotechnetium Compounds; D010091:Oximes; D012044:Regression Analysis; D019690:Technetium Tc 99m Exametazime; D015899:Tomography, Emission-Computed, Single-Photon; D014980:Xenon Radioisotopes
chemical_list: D015609:Organotechnetium Compounds; D010091:Oximes; D014980:Xenon Radioisotopes; D019690:Technetium Tc 99m Exametazime