SINGLES TRANSMISSION SCANS PERFORMED POST-INJECTION FOR QUANTITATIVE WHOLE-BODY PET IMAGING

Post-injection singles transmission scanning has been implemented in t he septumless PENN PET 240H scanner. The method uses a 6 mCi point tra nsmission source of Cs-137 at the axial center and 36 cm off transaxia l center of the camera field of view. Singles transmission scans of 1. 8 minutes per bed axial position provide similar scan count densities to 15 minute coincidence transmission scans with a 0.5 mCi Ge-68 rod t ransmission source. Scatter and emission contamination suppression are achieved by applying a narrow 662 keV transmission photopeak energy w indow. The residual 511 keV emission contamination constitutes a backg round of uniform spatial distribution. Accurate and low noise attenuat ion correction is achieved by segmenting the singles transmission imag es into lung and soft tissue volumes. Established 511 keV gamma ray at tenuation coefficients are then applied and these images are forward p rojected for attenuation correction. Expectation maximisation with ord ered subsets (OS-EM) reconstruction is performed for the emission data to improve image quality. Both the segmentation and OS-EM reconstruct ion maintain quantitative accuracy in the fully corrected emission ima ges compared to measured coincidence transmission correction. Thus, a clinical protocol involving 40 minutes of emission scans followed by 2 0 minutes of singles transmission scans allow the 60 cm of the human t orso to be fully scanned within 60 minutes. These quantitative whole b ody FDG PET images may then be used for tumor grading and assessment o f tumor response to treatment.