Organ distribution of thallium-201 during intravenous adenosine infusion: comparison with exercise

Thallium-201 (Tl-201) distribution during adenosine infusion was assessed quantitatively and compared with that of exercise imaging. Adenosine and exercise Tl-201 single-photon emission computed tomography (SPECT) were performed in 40 patients with suspected coronary artery disease. In the whole-body images (n = 5) and the unprocessed anterior projection images acquired as part of the initial imaging (n = 35), Tl-201 counts in the myocardium were normalized for the injected dose. Total heart counts were higher during adenosine infusion than during exercise (190 +/- 43 counts/MBq vs 145 +/- 31 counts/MBq, p < 0.01). A heart-to-lung count ratio between adenosine infusion and exercise was not different. A heart-to-liver count ratio was lower during adenosine infusion than during exercise (1.3 +/- 0.3 vs 2.3 +/- 0.5, p < 0.01). Regional Tl-201 uptakes at the inferior wall of the left ventricle during adenosine infusion were closely correlated with those uptakes during exercise (r = 0.94, p < 0.01, slope = 0.96). The sensitivity, specificity, and accuracy of adenosine Tl-201 SPECT for the detection of right coronary artery stenosis were comparable with those of exercise imaging. These results indicated that higher Tl-201 uptake in the liver during adenosine than during exercise did not interfere with the interpretation of myocardial images. Tl-201 counts in the myocardium that were larger during adenosine infusion than during exercise reflected a larger increase in coronary blood flow and thus resulted in better image quality.