Application of the OS-EM method to myocardial SPECT: evaluation of artifact reduction using heart phantom with liver object

Abstract

SPECT images reconstructed by the ordered subsets expectation maximization (OS-EM) method are known to have fewer artifacts induced by the nearly high-count background organs. The aim of this study was to determine whether the OS-EM method is effective in reducing artifacts induced by the high radioactivity of liver compared with the filtered back projection (FBP) method using a heart phantom with a liver object. Heart and liver phantoms were laid to overlap each other by 2 cm, and the liver/heart radioactivity (L/H) ratios were 0:1, 2:1, and 6:1. Short axial images of cardiac SPECT were reconstructed by OS-EM and the filtered back projection (FBP) method, and counts profiles were obtained for both methods. In both methods of image reconstruction, artifactual higher counts in the inferior wall of the heart were observed as the L/H ratio increased. When compared with the L/H ratio of 0:1, the increase in relative counts of the L/H ratio of 2:1 in the inferior wall showed a similar value for both methods (OS-EM: +9.7%, FBP: +11.6%). With the L/H ratio of 6:1, the OS-EM method showed a lesser increase in relative counts of the inferior wall than with the FBP method (OS-EM: +24.5%, FBP: +38.9%). Moreover, the areas of increased counts were smaller. In conclusion, the OS-EM method was thought to be more useful than the FBP method in reducing the increase in artifactual counts caused by the high radioactivity of liver.