ASSESSMENT OF TC-99(M)-TETROFOSMIN LUNG UPTAKE - A MODIFIED METHOD TOAVOID, THE CONTRIBUTION FROM HIGH CHEST-WALL ACTIVITY

Evaluation of lung uptake during routine Tc-99(m)-tetrofosmin myocardi al SPET (single photon emission tomography) studies may be hindered by substantial chest muscle uptake, particularly post-exercise. This stu dy investigated this proposal and analysed the various components of c hest activity that may add to the real lung uptake. Exercise SPET stud ies were performed on normal subjects using Tc-99(m)-tetrofosmin and c ompared with the results of Tc-99(m)-sestamibi and Tl-201 studies. The chest to heart count ratio (CHR) was calculated from the anterior SPE T projection and further subclassified into lung, anterior chest and p osterior chest to heart ratios (LHR, AHR, PHR) from the left anterior oblique (LAO) projection. On postexercise images, the Tc-99(m)-tetrofo smin CHR was significantly higher than that of Tl-201 and Tc-99(m)-ses tamibi. Both the Tc-99(m)-tetrofosmin AHR and PHR were higher than tho se of Tl-201 and Tc-99(m)-sestamibi. However, the LHR was similar for all three radiopharmaceuticals. In contrast, the rest Tc-99(m)-tetrofo smin images differed little from the Tl-201 and Tc-99(m)-sestamibi one s. Thus, Tc-99(m)-tetrofosmin lung uptake postexercise should be inter preted with caution, as chest muscle uptake is higher than normal. A m ore accurate evaluation of Tc-99(m)-tetrofosmin lung uptake is achieve d from the LAO projection, where the contribution from chest muscle co unts is much less than in the routinely used anterior projection. (C) 1998 Lippincott Williams & Wilkins).