A COMPARISON OF RESTING IMAGES FROM 2 MYOCARDIAL PERFUSION TRACERS

We have compared stress-redistribution and delayed rest thallium-201 with rest technetium-99m methoxyisobutylisonitrile (MIBI) tomograms in order to compare the tracers for the assessment of myocardial viability and to validate a rapid protocol combining the two tracers. We studied 30 consecutive patients with known or suspected coronary artery disease [group 1: 16 with normal left Ventricular function, mean left ventricular ejection fraction (LVEF) 55%, SD 6%; group 2: 14 with abnormal function, mean LVEF 28%, SD 8%]. (201)T1 was injected during infusion of adenosine followed by acquisition of conventional stress and redistribution tomograms. On a separate day, (201)T1 was injected at rest with imaging 4 h later. Tc-99m-MIBI was then given at rest and imaging was performed. Three images were compared: redistribution (201)T1, rest (201)T1, and rest Tc-99m-MIBI. Tracer activity was classified visually and quantitatively in nine segments and segments with > 50% activity were defined as containing clinically significant viable myocardium. Mean (+/- SD) global tracer uptake as a percentage of maximum was similar in group I (rest (201)T1 69% +/- 12%, redistribution (201)T1 69% +/- 15%, rest Tc-99m-MIBI 70% +/- 13%, ANOVA P > 0.05), but in group 2 mean tracer uptake was significantly greater in the rest (201)T1 images (59% +/- 16%) than in redistribution (201)T1 images (53% +/- 17%) or rest Tc-99m-MIBI images (53% +/- 19%) (ANOVA P = 0.02). Overall agreement for regional uptake score was excellent (kappa from 0.79 to 0.84), although there were a significant number of segments with less uptake shown by redistribution (201)T1 and by rest Tc-99m-MIBI than by rest (201)T1 in group 2 (P < 0.001). The number of segments with significant viable myocardium in group 1 was very similar between the three images (P > 0.05) but in group 2 rest (201)T1 identified significantly more segments as viable than the other images (McNemar P < 0.001). Thus (201)T1 and Tc-99m-MIBI provide similar information in patients without prior infarction and with normal left ventricular function (group 1), and a rapid protocol with stress (201)T1 injection and imaging followed immediately by rest Tc-99m-MIBI injection and imaging is feasible. In patients with abnormal left ventricular function and prior infarction (group 2), Tc-99m-MIBI may underestimate the extent of clinically significant viable myocardium.