CARDIAC AXIS CHANGE BETWEEN PRONE AND SUPINE POSITIONING MAY CONTRIBUTE TO DIFFERENCES IN TC-99(M)-MIBI MYOCARDIAL SPET IMAGING

The aims of this study were to assess the effect of prone and supine p ositioning on Tc-99(m)-MIBI myocardial SPET images and the contributio n of cardiac axis change. We compared 227 tomograms of patients imaged in the prone position with 227 tomograms of the same patients imaged in the supine position. For each tomographic session, the axis angle o f the heart was recorded using an in-house program. The results showed a significant change in the cardiac axis angle of 9 degrees in the tr ansaxial plane (P<0.001). This change in the cardiac axis correlated w ith differences in cardiac wall activity (wall activity when the patie nt was imaged in the prone position minus wall activity when the patie nt was imaged in the supine position). Our results suggest that factor s other than diaphragmatic movement and attenuation could account for the differences in wall activity observed when patients are imaged pro ne versus supine. Differences in the intensity of photon attenuation i n the heart itself, depending on the cardiac axis, could be a contribu ting factor. Quantitation of the variation in wall activity leads us t o suggest that Tc-99(m)-MIBI SPET should be performed in the prone pos ition to allow better visualization of the inferior and the septal wal ls. The anterior and lateral walls are better studied in the supine po sition. Images acquired in both the prone and supine positions would a llow the best assessment of all walls.