Design and performance of collimated coincidence point sources for simultaneous transmission measurements in 3-D PET

We have implemented a simultaneous emission-transmission measurement for th ree-dimensional positron emission tomography (3-D PET) using a collimated c oincidence point source design employing a fast, dedicated, reference detec tor close to the transmission source. This design reduces the effects of ra ndoms, scatter, dead time, and sensitivity loss on the emission data compar ed to previous implementations. It also greatly reduces the effect of emiss ion contamination of the transmission data compared to the use of rod sourc es. In this paper, we present performance characterizations of this measurement technique on both the Siemens/CTI ECAT ART and PET/SPECT tomographs. The m ain effect of the transmission sources on the emission measurement is an in creased randoms rate, which leads to a 10-25% reduction in NECR at specific activities >2 kBq/mL in a 21-cm-diameter phantom on the PET/SPECT. Emissio n contamination effects on the transmission measurement are estimated to be less than I % for up to 20 kBq/mL in a 21-cm phantom on the PET/SPECT. Bot h the emission and transmission NECR are dominated by the effects of random s. Considering the effects of both emission and transmission noise on the f inal corrected image, it appears that 3-6 kBq/mL of emitter concentration i s an optimal imaging range for simultaneous acquisitions. We present the fi rst images of a normal volunteer using this system on a Siemens/CTI PET/SPE CT tomograph.