Myocardial uptake and kinetic properties of technetium-99m-Q3 in dogs.
We postulated that 99mTc-Q3, a cationic imaging agent, produces myocardial activity related to myocardial blood flow during myocardial ischemia and pharmacologic coronary artery vasodilation, and shows little or no myocardial redistribution over 4 hr after intravenous injection.


METHODS
In six Group 1 dogs, the chest was opened, the left circumflex coronary artery was acutely ligated, and dipyridamole (0.32, 0.56 or 0.84 mg/kg) was infused into the right atrium, followed by 10 mCi of 99mTc-Q3. Myocardial blood flow was measured by radiolabeled microspheres. The animals were euthanized and 357 myocardial samples were assayed in a well counter for 99mTc activity. One week later, radiolabeled microsphere activity was counted and myocardial blood flow calculated. In nine Group 2 dogs, a variable occluder was placed around the left circumflex coronary artery and an ischemic level of circumflex blood flow was maintained constant over 4 hr as measured by an ultrasonic flow meter. Dipyridamole (0.56 mg/kg) was then infused into the right atrium followed by 10 mCi of 99mTc-Q3. Gamma camera images were acquired at 5, 15, 30, 60, 120 and 240 min following 99mTc-Q3 injection. Microsphere blood flow and endocardial biopsies (n = 6 dogs) were performed at 30, 60, 120 and 240 min following 99mTc-Q3 injection.


RESULTS
In the Group 1 animals, 99mTc activity (y) was related to myocardial blood flow (x) from 0 to 6.1 ml/min/g by the relationship y = 0.83X + 0.18, r = 0.95, p = 0.0001. The scintigraphic ratio of myocardial perfusion defect zone counts-to-normal myocardial zone counts (0.54 +/- 0.05 at 30 min) remained constant over 4 hr, as did technetium counts from direct endocardial sampling. Scintigraphic count ratios allowed discrimination between perfusion defect and normal myocardial regions beginning at 5 min following 99mTc-Q3 injection.


CONCLUSIONS
Over a range of myocardial blood flows from 0 to 6.1 ml/min/g, 99mTc-Q3 myocardial activity is related to myocardial flow at the time of tracer injection. Technetium-99m-Q3 shows no evidence of myocardial redistribution over a 4-hr period.
Gerson
M C
MC
Department of Internal Medicine, Eugene L. Saenger Radioisotope Laboratory, University of Cincinnati, Ohio 45267.
Millard
R W
RW
McGoron
A J
AJ
Gabel
M
M
Washburn
L C
LC
Biniakiewicz
D
D
Elder
R C
RC
Deutsch
E
E
Walsh
R A
RA
D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology; D004176:Dipyridamole; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging*; D008297:Male; D008863:Microspheres; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging*; D015609:Organotechnetium Compounds; D010720:Phosphines; D011877:Radionuclide Imaging; D013997:Time Factors
D015609:Organotechnetium Compounds; D010720:Phosphines; C081212:technetium Tc 99m Q3; D004176:Dipyridamole