TRANSMISSION-BASED SCATTER CORRECTION OF 180-DEGREES MYOCARDIAL SINGLE-PHOTON EMISSION TOMOGRAPHIC STUDIES

Meaningful comparison of single-photon emission tomographic (SPET) rec onstructions for data acquired over 180 degrees or 360 degrees can onl y be performed if both attenuation and scatter correction are applied, Convolution subtraction has appeal as a practical method for scatter correction; however, it is limited to data acquired over 360 degrees, A new algorithm is proposed which can be applied equally well to data acquired over 180 degrees or 360 degrees The method involves estimatin g scatter based on knowledge of reconstructed transmission data in com bination with a reconstructed estimate of the activity distribution, o btained using attenuation correction with broad beam attenuation coeff icients, Processing is implemented for planes of activity parallel to the projection images for which a simplified model for the scatter dis tribution may be applied, based on the measured attenuation. The appro priate broad beam (effective) attenuation coefficients were determined by considering the scatter buildup equation. It was demonstrated that narrow beam attenuation coefficients should be scaled by 0.75 and 0.6 5 to provide broad beam attenuation coefficients for technetium-99m an d thallium-201 respectively. Using a thorax phantom, quantitative accu racy of the new algorithm was compared with conventional transmission- based convolution subtraction (TDCS) for 360 degrees data, Similar hea rt to lung contrasts were achieved and correction of 180 degrees data yielded a 10.4% error for cardiac activity compared to 5.2% for TDCS, Contrast for myocardium to ventricular cavity was similarly good for s catter-corrected 180 degrees and 360 degrees data, in contrast to atte nuation-corrected data, where contrast was significantly reduced, The new algorithm provides a practical method for correction of scatter ap plicable to 180 degrees myocardial SPET.