Temporal changes in sequential quantitative thallium-201 imaging following myocardial infarction in dogs: comparison of four- and twenty-four-hour infarct images.

Thallium-201 ((201)T1) myocardial perfusion imaging allows definition of zones of myocardial infarction and ischemia. The temporal changes in sequential quantitative (201)T1 infarct imaging was studied 4 and 24 hours in dogs subjected to closed-chest anterior wall myocardial infarction. A temporal decrease in (201)T1 imaged infarct areas was noted in 10 of 13 animals. In no animal did the infarct area increase. The imaged infarct area decreased by an average of 30% from 12.9 ± 6.2 cm(2) at 4 hours to 9.1 ± 5.1 cm(2) at 24 hours (p < 0.001), and involved 34 ± 16% of the total (201)T1 left ventricular distribution at 4 hours and 22 ± 14% at 24 hours (p < 0.001). The magnitude of temporal change in imaged infarct area was not predicted by initial image defect or final histopathologic infarct size. Thus, the results of (201)T1 infarct imaging in the early period of infarction are clearly dependent upon the time at which the procedure is performed.