SPECT reconstruction using uniform and object-specific attenuation maps with emission-transmission CT

A prototype emission-transmission computed tomographic (ETCT) system was used to acquire both radionuclide-emission and dual-energy X-ray transmission data of a thorax-like phantom. An object- and energy-specific attenuation map was synthesized from the dual-energy X-ray data, and then incorporated into a maximum likelihood-expectation maximization (ML-EM) algorithm to reconstruct an attenuation-corrected single photon emission computed tomography (SPECT) image. SPECT images reconstructed with no attenuation correction, or with a uniform water-equivalent map, contained increased count levels in the lung region and reduced count levels in the cardiac region as compared to the radioactivity concentrations contained in the phantom. Correction with an object-specific attenuation map improved the accuracy of the reconstruction, but overestimated the activity in the cardiac chamber by about 10%