It was known that conventional stress-redistribution imaging was not adequate for detection of severely ischemic but viable myocardium. Albeit the gold criteria of viable myocardium is the presence of metabolism which can be detected by PET, reinjection technique was reported to be able to identify most, if not all, of viable myocardium. Because reinjection imaging is performed immediately after redistribution imaging, an additional redistribution could be happened if we follow the patient longer. To prove the guess authors performed an additional delayed imaging 24 hours after reinjection of 201T1.

Subject patients were 20 ischemic heart disease patients who showed irreversible perfusion defect(s) on standard pharmacologic(dipyridamole) stress-redistribution images. Immediately after the redistribution images were obtained, 37 MBq thallium was injected at rest, and images were reacquired at 10 minutes and 24 hours after reinjection. Four sets of images(stress, redistribution, reinjection and delayed images) were then analyzed qualitatively and quantitatively. Left ventricle was arbitrarily divided into 9 segments(apex, proximal and distal portions of anterior, septal, inferior and lateral walls).

These were 45 irreversible perfusion defects in 20 subject patients, of which 21(46.7%) showed improved thallium uptake after reinjection. Among these 21 segments 2 demonstrated further improvement of uptake on 24-hour delayed images, of the 24 regions determined to have persistent defects after reinjection. 10(41.7%) showed improved uptake on delayed images.

In addition to reinjection imaging, 24-hour delayed imaging after reinjection was also helpful to identify severely ischemic but viable myocardium.