AN EMISSION-BASED TECHNIQUE FOR OBTAINING ATTENUATION CORRECTION DATAFOR MYOCARDIAL SPECT STUDIES

In this paper, a technique is described for obtaining the information needed to perform attenuation correction in the thorax entirely from a n emission study. This technique is based on the observation that the variation in soft tissue and lung attenuation coefficients is small am ong individuals. Thus only the outer contours of the body and lungs ne ed be determined for obtaining the attenuation map. The contours are d etermined by using Tc-99m-macroaggregated albumin (MAA) to locate the lungs and an external source wrapped about the chest to locate the bod y boundary. Simulation studies were performed to investigate how error s in the presumed tissue attenuation coefficients affect the accuracy of the correction. Body and lung attenuation coefficients were varied from 20% less to 20% more than the coefficients used in the correction s. Over this range, there was less than a 15% alteration in the relati ve distribution of counts in the left ventricle. To test clinical feas ibility, seven patients referred for clinical myocardial perfusion stu dies were scanned before and after the placement of the body source an d the administration of Tc-99m-MAA. Reconstructed images from these st udies showed clear demarcation of all body and lung boundaries. The pr esence of Tc-99m-MAA in the lungs had no significant effect on the cli nical interpretation of the single photon emission computed tomographi c (SPECT) studies. It is concluded that this technique is feasible for clinical application and that it offers important advantages over oth er current methods.