Comparative study of three different approaches on the estimation of the lung-heart ratio in thallium 201 scintigrams in relation to the extent of coronary artery disease and left ventricular function

Uptake of thallium 201 (²⁰¹Tl) in the lungs has been proposed as a measure of left ventricular dysfunction with exercise. To study this hypothesis, we compared the lung/-heart (LH) ratio assessed from anterior planar images (ANT-P), from anterior images obtained during single photon emission tomography (SPET) acquisition (ANT-T) and from short-axis tomographic cross-sections (CS) in early post-exercise thallium 201 scintigrams. The study population consisted of 54 prepercutaneous transluminal coronary angioplasty (PTCA) studies (82% with single-vessel disease), 50 post-PTCA studies, 33 pre-coronary artery bypass surgery (CABG) studies (71 % with three-vessel disease), 30 post-CABG studies and 30 patients with a left ventricular dysfunction (LVD) due to an acute myocardial infarction; 18 individuals with a low likelihood of coronary artery disease (CAD) served as a control group. The results demonstrated that, on average, the LH ratios obtained from ANT-P and ANT-T were not significantly different for all study groups; these ratios increased significantly with ischaemia and with LVD relative to non-ischaemic situations. However, the LH ratios in CS did not show a relation with ischaemia nor with LVD and differed significantly from the LH-ratios assessed from the anterior approaches. Each of the three approaches (ANT-P, ANT-T, CS) was characterized by large overlaps of LH ratios for the different study groups. In conclusion, the LH ratio should be determined from ANT-P or ANT-T projection images, not CS. However, due to large overlaps in the measurement data, it is not a clinically useful parameter for the detection of CAD or LVD in the individual patient.