The (F)utility of the thallium-201 quantitative lung/myocardial ratio in the detection of coronary artery disease

Pulmonary thallium-201 uptake following dipyridamole-exercise combination compared with single modality stress testing

Angiographic and clinical determinants of pulmonary uptake of thallium-201 were assessed in a laboratory setting where supine bicycle exercise is used for stress testing in the absence of limiting pharmacologic or physical factors, and where symptom-limited exercise is added to intravenous dipyridamole infusion in other cases. Angiographic correlation was available in 400 patients, including 130 tested with exercise, 94 in whom only handgrip or abbreviated bicycle exercise could be used after dipyridamole, and 176 in whom intravenous dipyridamole was combined with a significant level of exercise. For each test mode, lung/myocardial ratios on the immediate image were highly correlated (p less than or equal to 0.001) with a score based on the number of critical coronary artery stenoses, with grading by contrast ventriculography, and with the number of stenosed (greater than or equal to 50%) arteries; relationships (p less than 0.05) to history of myocardial infarction and to gender were also present. Multiple regression analysis showed the critical stenosis score and ventricular dysfunction to be the only significant determinants. When dipyridamole based tests were compared with exercise, curves of receiver-operating characteristics showed a tendency to better diagnostic performance. When dipyridamole is incorporated in stress testing, the value of increased lung uptake as an ancillary diagnostic sign is similar to that established for exercise.

A new method for quantification of pulmonary thallium uptake in myocardial SPECT studies

Quantified pulmonary thallium 201 (Tl) uptake was assessed in 32 normal subjects and 66 patients with suspected coronary artery disease (CAD) by a new method utilizing SPECT acquisition data. In 26 subjects pulmonary uptake was assessed with both SPECT and planar techniques. Pulmonary/myocardial (PM) ratios for the whole right lung (PM1) and for the upper left lung (PM2) were computed and compared with stress test, coronary angiography, radionuclide angiography (ERNA), and quantified Tl single photon emission computed tomography (SPECT) results. Excellent correlation between pulmonary uptake assessed by planar and SPECT technique was disclosed (r = 0.92). The PM ratios (PM1/PM2) sensitivity and specificity in patients with CAD were 88%/92% and 60%/70%, for predicting perfusion abnormalities 90%/87% and 88%/88%, and an inverse correlation to left ventricular ejection fraction (LVEF) was found (r = -0.40/r = -0.37, P less than 0.01). Significant correlations to coronary angiography findings (r = 0.54/r = 0.49, P less than 0.001) and to number of vessel territories with abnormal perfusion (r = 0.70/r = 0.69, P less than 0.001) were seen. Thus, pulmonary Tl uptake can be assessed in SPECT studies. The new method's discriminative ability seems higher than that of the standard planar techniques currently employed. Positive correlations to coronary angiography findings and even stronger ones to perfusion abnormalities were observed.

A comparison of myocardial thallium-201 image quality after either dipyridamole or exercise stress

Exercise and dipyridamole provide two mechanistically different stress techniques for thallium-201 imaging. To date, comparisons of the two have relied solely on assessments of clinical results. However, because diagnostic accuracy ultimately depends on image quality, this study was undertaken to compare the image quality obtained by both techniques. The left anterior oblique images of 30 patients, who had thallium imaging after intravenous dipyridamole (0.56 mg kg-1 over 4 min) were compared with those of 30 patients who were imaged after symptom limited, Bruce protocol, treadmill exercise in the same time period. Myocardial and lung-background thallium uptake were compared after stress and on redistribution. The ratio of the best segmental myocardial thallium uptake (M) to that in a fixed lung-background region (B) was taken as an index (M/B) of image quality. Myocardial thallium uptake was significantly higher after dipyridamole than after exercise (P less than 0.001). Lung-background thallium uptake, however, was also higher (P less than 0.001) so that the resulting image quality indices (M/B) were similar (P = NS). The redistribution images gave the same results. In both techniques myocardial and lung-background thallium uptake counts dropped significantly from stress to redistribution images, but because they declined at similar rates, the resulting image quality index (M/B) remained unchanged. Adverse effects occurred less frequently in the dipyridamole stressed group. Thallium images performed after dipyridamole stress are at least equivalent in image quality to those after exercise stress. This technical study further strengthens the clinical case for the use of the dipyridamole stress technique in routine diagnostic imaging.