A comparison of qualitative and quantitative analysis of thallium reinjection images

It is well known that TI-201 reinjection imaging contributes in verifying myocardial viability. 20 patients were studied, 4 females and 16 males, aged 43 to 67 years (average 56.5 years). In 6 patients coronary ischaemia was suspect clinically, while in the remaining 14 patients myocardial infarction was verified by ECG and enzymes at least three months earlier. One patient had previously undergone PTCA. 2 mCi of Tl-201 were injected during stress test on a treadmill (Bruce protocol). Imaging was started within 9 minutes of injection, and redistribution imaging was performed 4 hours after injection. All our patients had one or more persistent defects on stress-redistribution imaging. 1 mCi of Tl-201 was reinjected immediately following redistribution imaging and reinjection images were performed 30 minutes later. The studies were analyzed qualitatively and quantitatively by two independent observers. Altogether, there were 28 irreversible defects on stress-redistribution scintigraphy. On qualitative analysis 10 of 28 (36%) showed an increase in Tl-201 uptake, while 18(64%) showed no changes. Quantitative analysis showed 4 (14%) defects with an increase of thallium uptake after reinjection, while 24 (86%) of irreversible defects in stress-redistribution imaging showed no change. The qualitative analysis is superior as compared to quantitative because of the problems related primarily to the background correction on reinjection images. (author)