title: Flow versus uptake comparisons of thallium-201 with technetium-99m perfusion tracers in a canine model of myocardial ischemia.
abstract: We investigated the myocardial flow kinetics of six putative radioperfusion agents (99mTc-Q3, 99mTc-Q4, 99mTc-Q12, 99mTc-sestamibi, 99mTc-tetrofosmin and 99mTcN-NOET) and 201Tl in a canine model of myocardial ischemia with pharmacologic coronary artery vasodilation.
  
  
  METHODS
  In 31 open-chest dogs with acute coronary occlusion, dipyridamole (approximately 0.56 mg/kg) was infused intravenously, followed by a perfusion tracer injection and radioactive microspheres for myocardial blood flow (MBF) measurement. The paired data were normalized using three techniques; average, normal or maximum myocardial tracer activity and MBF.
  
  
  RESULTS
  The upper limit of MBF obtained for the group of tracers ranged from 4.2 ml/min/g to 8.2 ml/min/g. There was a statistically significant (p < 0.0001) linear correlation (r = 0.87-0.98) between the normalized myocardial activity and the normalized MBF values of each of the tracers. The slope of the curve normalized by average for 201Tl (0.83) was greater than those for the 99mTc tracers, and the intercept (0.07) was lower than those for the 99mTc tracers. Slopes and intercepts for the 99mTc agents were as follows: 99mTc-Q3, 0.81 and 0.18; 99mTc-Q4, 0.61 and 0.41; 99mTc-Q12, 0.63 and 0.39; 99mTc-sestamibi, 0.62 and 0.34; 99mTc-tetrofosmin, 0.68 and 0.32; and 99mTcN-NOET, 0.71 and 0.29, respectively.
  
  
  CONCLUSIONS
  In an anesthetized open-chest canine model of regional myocardial ischemia with dipyridamole induced hyperemia, 201Tl shows a more ideal relationship between tracer uptake and MBF than do the 99mTc-based agents. Of the various 99mTc-based imaging agents studied, the myocardial flow kinetics of 99mTc-Q3 appear to be closest to ideal. This relationship is maintained regardless of the normalization technique used. This may, in theory, imply a higher sensitivity in discerning ischemic from normal myocardium and a role in diagnostic nuclear imaging for 99mTc-Q3.
authors.affiliation: Department of Internal Medicine, University of Cincinnati College of Medicine, Ohio, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Meleca
authors.forename: A J
authors.initials: AJ
authors.lastname: McGoron
authors.forename: M C
authors.initials: MC
authors.lastname: Gerson
authors.forename: R W
authors.initials: RW
authors.lastname: Millard
authors.forename: M
authors.initials: M
authors.lastname: Gabel
authors.forename: D
authors.initials: D
authors.lastname: Biniakiewicz
authors.forename: N J
authors.initials: NJ
authors.lastname: Roszell
authors.forename: R A
authors.initials: RA
authors.lastname: Walsh
mesh_terms: D000818:Animals; D003326:Coronary Circulation / Q000502:physiology; D004176:Dipyridamole; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging*; D008297:Male; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000503:physiopathology; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D013794:Thallium Radioisotopes / Q000493:pharmacokinetics; D014665:Vasodilator Agents
chemical_list: D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D013794:Thallium Radioisotopes; D014665:Vasodilator Agents; D004176:Dipyridamole