9:15-9:30. A Clinical Evaluation of Segmented Attenuation Correction

Segmented attenuation correction (SAC) has been introduced as a method of reducing transmission scan times without degrading the quality of PET images. Presented are the results of a clinical evaluation of a SAC algorithm implemented on the GE Advance PET system. FDG whole body patient emission scans of eight minute duration were acquired. Dynamic transmission (Tx) scans of 5 frames and 6 minute total duration were acquired and rebinned into Tx scans of 2, 3, 4, 5 and 6 minute duration. Images (I) were generated using iterative reconstruction with measured attenuation correction (MAC) or SAC for all Tx scans-denoted as I(Tx6MAC), I(Tx6SAC), etc. Anthropomorphic phantom data was also acquired and reconstructed using the same methodology. Images were evaluated quantitatively using the normalized mean square error (NMSE) of different regions and the variance and bias of liver activity. I(Tx6MAC) served as the reference. A blinded observer ranked image quality. The NMSE increased as the Tx duration decreased; for patient images the NMSE was typically 20% and 40% greater for I(Tx3SAC) and I(Tx2SAC) than I(Tx6SAC) respectively. The NMSE of the MAC images increased much more rapidly as the Tx duration decreased. Similar trends were found for the variance in the liver. Bias in liver activity of the SAC images was approximately -8% for large patients. The observer consistently preferred SAC images over MAC images. SAC images demonstrated improved boundary delineation and reduced noise in areas of homogeneous high activity background. Areas of discordance were projected into areas of large difference between Tx and segmented Tx sinograms. This study has validated the use of SAC with short Tx scans. Images reconstructed with Tx scans of 3 minutes were not compromised with noise or severe artifacts.