Myocardial Imaging with Thallium-201: Effect of Cardiac Drugs on Myocardial Images and Absolute Tissue Distribution

TLDR: In this article, the effect of dipyridamole on myocardial-to-background ratio (M/Bk) and tissue uptake of thallium-201 was investigated.

Abstract: Four cardioactive drugs were studied to determine their effect on the thallium-201 myocardial image. Four unanesthetized dogs were imaged weekly for 14 wk following the administration of dipyridamole, digoxin, furosemide, or propranolol. The myocardial-to-background ratio (M/Bk) was used to define the effects of the drugs on the Tl-201 image. Under control conditions, the M/Bk was 1.99 ± 0.15, which is similar to that in humans. Dipyridamole (0.5 mg/kg i.v.) increased M/Bk to 2.65 ± 0.5. Digoxin, propranolol, and furosemide produced no significant changes in M/Bk. The relationship between (a) M/Bk derived from external imaging and (b) tissue uptake of Tl-201 was then tested in 12 dogs. Tl-201 concentration (% uptake/gm of tissue) in the heart was significantly elevated after dipyridamole administration as compared with control. Left-ventricular Tl-201 concentration increased 60% (p The effect of dipyridamole on M/Bk and tissue uptake of Tl-201 suggests that regional perfusion abnormalities may be detected by imaging following coronary vasodilator administration as an alternative to exercise stress. The propranolol data suggest that beta-blockers will have little effect on the resting Tl-201 image.