Correction for emission contamination in transmission scans for the High Resolution Research Tomograph

The High Resolution Research Tomograph PET scanner is equipped with a moving Cs-137 transmission point source emitting 662 keV single photons. During postinjection transmission imaging 511 keV emission photons can be detected in the transmission window leading to gross underestimation of the reconstructed mu-value. Using cylindrical phantoms, methods to compensate for this emission contamination (EC) were investigated including histogram-based scaling and segmentation with varying transmission window settings. Furthermore, the effects of subtracting a uniform or nonuniform EC estimation prior to transmission reconstruction were quantified. In conclusion, EC during HRRT transmission scans can lead to gross underestimation of mu-values, and the most accurate way to compensate for this is to combine nonuniform EC subtraction with image segmentation.