Evaluation of lung uptake during routine Tc-99(m)-tetrofosmin myocardial SPET (single photon emission tomography) studies may be hindered by substantial chest muscle uptake, particularly post-exercise. This study investigated this proposal and analysed the various components of chest activity that may add to the real lung uptake. Exercise SPET studies were performed on normal subjects using Tc-99(m)-tetrofosmin and compared with the results of Tc-99(m)-sestamibi and Tl-201 studies. The chest to heart count ratio (CHR) was calculated from the anterior SPET projection and further subclassified into lung, anterior chest and posterior chest to heart ratios (LHR, AHR, PHR) from the left anterior oblique (LAO) projection. On postexercise images, the Tc-99(m)-tetrofosmin CHR was significantly higher than that of Tl-201 and Tc-99(m)-sestamibi. Both the Tc-99(m)-tetrofosmin AHR and PHR were higher than those of Tl-201 and Tc-99(m)-sestamibi. However, the LHR was similar for all three radiopharmaceuticals. In contrast, the rest Tc-99(m)-tetrofosmin images differed little from the Tl-201 and Tc-99(m)-sestamibi ones. Thus, Tc-99(m)-tetrofosmin lung uptake postexercise should be interpreted with caution, as chest muscle uptake is higher than normal. A more accurate evaluation of Tc-99(m)-tetrofosmin lung uptake is achieved from the LAO projection, where the contribution from chest muscle counts is much less than in the routinely used anterior projection. (C) 1998 Lippincott Williams & Wilkins).
