Implementation of Histogram Based Soft-tissue Segmentation for Single Spiral Transmission Scanning in Whole Body PET

3D continuous emission and spiral transmission (CEST) scanning provides a high-throughput whole-body PET study using two dedicated detectors for 3D emission and single transmission with continuous bed movement. Since post-injection single transmission data contains emission contamination (EC) and transmission scatter components (TSC), the transmission detector was designed to have a short axial extent with a highly collimated ¹³⁷Cs point source, and be implemented using a realtime EC correction method. However, transmission images can be still affected by residual EC and TSC, depending on patient size and dose injected. This results in slight variations in attenuation coefficients, depending on the patient´s axial position. In this study, we developed a new soft-tissue segmentation (STS) method based on histogram scaling at each axial position of the spiral transmission. Peaks, corresponding to soft-tissue in a histogram of attenuation coefficients, were found at each axial position and the transmission image was scaled using the ratio of soft-tissue histogram peaks to the theoretical water attenuation coefficient. In scaled transmission images, the pixel values near the soft-tissue peak were replaced with the theoretical water attenuation coefficient. Quantitative evaluation was performed of the transmission images obtained under various acquisition conditions, both with and without the proposed STS method. Regarding final imaging performance, emission images reconstructed using both STS attenuation correction and hybrid scatter correction were evaluated. Results showed that the proposed STS method for spiral transmission scanning provided quantitative images independent of object size and containing activity concentration.