Bh. Hasegawa et al., OBJECT-SPECIFIC ATTENUATION CORRECTION OF SPECT WITH CORRELATED DUAL-ENERGY X-RAY CT, IEEE transactions on nuclear science, 40(4), 1993, pp. 1242-1252
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
.