CHARACTERIZATION AND CORRECTION OF PULSE PILE-UP IN SIMULTANEOUS EMISSION-TRANSMISSION COMPUTED-TOMOGRAPHY

We have developed an emission-transmission CT (ETCT) system capable of both single-photon emission computed tomography (SPECT) imaging and x -ray transmission CT imaging using a common photon counting detector. In principle, SPECT and x-ray CT projection data can be acquired simul taneously with the ETCT system; however, doing so results in contamina tion of the SPECT projection data due to pulse pile-up caused by the r elatively high x-ray fluence rate. In this study, we characterize the effects of pulse pile-up for simultaneous ETCT imaging through compute r simulation and experimental studies. We demonstrate that pulse pile- up in the SPECT energy window can be well approximated by a simple qua dratic relationship between the pile-up rate and the x-ray fluence rat e for sufficiently small x-ray fluence rates. Using this quadratic rel ationship, we developed a simple pile-up correction scheme that subtra cts the pile-up counts from the emission data and also truncates the e xterior regions of the emission projection data. Analysis of differenc e images and profiles indicate that this method permits us to reconstr uct SPECT images with no apparent noise or resolution degradation in c omparison to those obtained via sequential emission and transmission s cans. (C) 1996 American Association of Physicists in Medicine.