ATTENUATION EFFECTS IN TC-99M-MIBI SPECT AT EXERCISE (360-DEGREES ACQUISITION) - COMPARISON OF SUPINE AND PRONE IMAGING

Due to the higher photon energy of Tc-99m as compared to Tl-201 attenuation effects are expected to be less prominent in SPECT imaging using Tc-99m-labelled isonitriles. Reduced Tc-99m-MIBI uptake has been observed especially in male patients despite low probability of coronary artery disease. 56 patients were investigated in prone and supine position after bicycle excercise. Inclusion criterium was the identical location of the ROI with maximal tracer uptake in prone and supine imaging. In prone position Tc-99m-MIBI uptake was significantly higher in the posterior wall as compared to supine imaging (p <.001). The underlying cause of the apparent increase in tracer uptake of the posterior wall was a decrease in count density in the region of maximal uptake (p <.01) while the count densities in the posterior wall were unchanged (p = NS). Relative uptake values in apical and septal regions of the anterior wall significantly decreased in prone imaging. SPECT imaging in prone position is useful in minimizing attenuation artifacts. However, because a deterioration in the anterior wall cannot be excluded, studies that compare the sensitivities and specificities for the different coronary arteries are required before general prone imaging can be recommended.