Effect of reconstruction arc in myocardial SPECT imaging. Comparison between 180deg and 360deg arc

A series of thallium-201 (201Tl) and technetium-99m (99mTc) myocardial perfusion images with or without perfusion defects were acquired by 360deg arc using a triple-head camera. The vertical long, horizontal long, and short axis images of 201Tl and 99mTc with 360deg, 180deg, and opposite 180deg were identically reconstructed and reoriented without attenuation correction. in order to detect the detailed differences between 360deg (30deg-390deg) and 180deg (30deg-210deg) images, the opposite 180deg (210deg-30deg) images were utilized. Opposite 180deg images revealed the contribution of those to the 360deg images. In the normal perfusion images, the CV (coefficient of variation) of the counts in 360deg images with 201Tl by the segments was larger than 180deg images. On the contrary, the CV of the counts in 360deg images with 99mTc was smaller than 180deg images. This difference, caused by the difference of photon energy, were detected mainly as the extent of counts decreasing in the deep segments in the opposite 180deg images. Lesion contrasts of the opposite 180deg images were lower than those of 180deg images due to distance related collimator response (the detector response of the collimated gamma camera varies with source-to-detector distance) and scatter. Therefore, lesion contrasts were more decreased in the 360deg images compared with those of 180deg images, especially in the segments of lateral and anterior walls. The differences in lesion contrasts between 201Tl and 99mTc images were mainly in the segments of inferior and posterior walls (p<0.05). Lesion contrast was dependent on the location of the perfusion defects, reconstruction arc, and photon energy. (author)