title: Kinetic properties of 99mTc-Q12 in canine myocardium.
abstract: BACKGROUND
  99mTc-Q12 is a new Tc(III) perfusion imaging agent that permits prompt myocardial visualization in humans. We postulated that 99mTc-Q12 myocardial activity is related to actual myocardial blood flow during conditions of myocardial ischemia and pharmacological coronary artery vasodilation and that 99mTc-Q12 shows little or no myocardial redistribution as long as 4 hours after intravenous injection.
  
  
  RESULTS
  In seven anesthetized, open chest dogs, the left circumflex coronary artery was occluded, and dipyridamole (0.32 or 0.56 mg/kg) was infused into the right atrium, followed by 10 mCi of 99mTc-Q12. Myocardial blood flow was measured by radiolabeled microspheres. The animals were euthanized, and a total of 315 myocardial samples were assayed in a well counter for 99mTc activity. One week later, radiolabeled microsphere activity was determined, and myocardial blood flow was calculated. 99mTc activity (y) was related to myocardial blood flow (x) from 0 to 2 mL.g-1 x min-1 by the relation y = 0.64x + 0.35 (r = .88, P = .0001). In 14 additional anesthetized, open chest dogs, an occluder was placed around the left circumflex coronary artery, and an ischemic level of circumflex blood flow was maintained constant over 4 hours as measured by an ultrasonic flowmeter. Dipyridamole (0.56 mg/kg) was infused intravenously beginning 15 minutes after coronary occlusion and then followed by 10 mCi of 99mTc-Q12. Gamma camera images, hemodynamics, microsphere blood flow, and endocardial biopsies (latter in six dogs) were performed at 30, 60, 120, and 240 minutes after 99mTc-Q12 injection. Myocardial blood flow in the distribution of the left anterior descending artery decreased by 29.6% from 30 to 240 minutes (P < .05), whereas left circumflex blood flow increased by 40.4% from 30 to 120 minutes (P < .05) as the dipyridamole hemodynamic effects dissipated. Nevertheless, the ratio of myocardial perfusion defect zone counts to normal myocardial zone counts remained constant over 4 hours, as did the technetium counts from the needle biopsy endocardial samples.
  
  
  CONCLUSIONS
  Over a limited range of myocardial blood flows from 0 to approximately 2 mL.g-1 x min-1, 99mTc-Q12 myocardial activity is related to actual myocardial flow at the time of tracer injection. 99mTc-Q12 shows no evidence of myocardial redistribution.
authors.affiliation: Division of Cardiology, University of Cincinnati, Ohio.
authors.forename: M C
authors.initials: MC
authors.lastname: Gerson
authors.forename: R W
authors.initials: RW
authors.lastname: Millard
authors.forename: N J
authors.initials: NJ
authors.lastname: Roszell
authors.forename: A J
authors.initials: AJ
authors.lastname: McGoron
authors.forename: M
authors.initials: M
authors.lastname: Gabel
authors.forename: L C
authors.initials: LC
authors.lastname: Washburn
authors.forename: D
authors.initials: D
authors.lastname: Biniakiewicz
authors.forename: D
authors.initials: D
authors.lastname: Blankenship
authors.forename: W H
authors.initials: WH
authors.lastname: Mallin
authors.forename: R C
authors.initials: RC
authors.lastname: Elder
mesh_terms: D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects; D004176:Dipyridamole; D004285:Dogs; D005663:Furans / Q000493:pharmacokinetics; D006321:Heart / Q000000981:diagnostic imaging*; D008297:Male; D008863:Microspheres; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging*; D009206:Myocardium / Q000378:metabolism; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D013997:Time Factors
chemical_list: D005663:Furans; D015609:Organotechnetium Compounds; C078496:technetium Tc 99m Q12; D004176:Dipyridamole