A METHOD TO CORRECT MYOCARDIAL SPECT WITH TC-99M COMPOUNDS FOR SCATTER AND ATTENUATION WITHOUT TRANSMISSION

Aim: A new strategy is introduced for a double-head gamma-camera to ca lculate and to correct for attenuation distribution from countrates of backscattered radiation of Tc-99m in the human thorax/myocardium set ting. The intention was to gain segmented and calibrated images of dis tribution employing the structures of lungs and other tissues; so that attenuation may be subsequently corrected by the method of Chang. Met hods: Acquisition was done simultanously in three energy windows for T c-99m to receive both emitted and scattered radiation. The acquired pr ojections were used to calculate the attenuation distribution and to e xecute a scattercorrection by the method of Ogawa et. al. By measuring phantoms and evaluating a set of patient studies, quality for both of the approaches towards attenuated distribution and the quality of att enuation correction was tested and an optimal setting for parameters i nvolved was selected. Results: The procedure adequately approaches the correction for both emitted and scattered radiation in SPECT, as expe rienced in phantom and patient studies. Clinical usefulness was prelim inary documented in selected cases. In normal perfusion, distribution was more homogenous. Perfusion defects appeared more definitive Proble ms occurred in high adjacent non-target activity (e.g., in the gallbla dder) and with low countrate statistics. Conclusion: Myocardial Tc-99m MIBI SPECT may be effectively corrected for both attenuation and scat ter without an additional transmission device.