OBJECT-SPECIFIC ATTENUATION CORRECTION OF SPECT WITH CORRELATED DUAL-ENERGY X-RAY CT

We have developed a prototype emission-transmission computed tomograph ic (ETCT) system, which can acquire both radionuclide-emission and dua l-energy X-ray transmission data. The dual-energy X-ray data are used to synthesize an object- and energy-specific attenuation map which is incorporated into an ML-EM algorithm to reconstruct an attenuation-cor rected SPECT image. The technique was applied to a thorax-like phantom with regions simulating lung, background and cardiac regions, and bon e. SPECT images reconstructed with no attenuation correction, or with a uniform water-equivalent map, contained increased count levels in th e lung region and reduced count levels in the cardiac region as compar ed with the radioactivity concentrations contained in the phantom. Use of an object-specific attenuation map improved the accuracy of the re construction, but overestimated the activity in the cardiac chamber by about 10%. This error was reduced to about 5% when the attenuation co efficients were modified to include the effects of scattered radiation .