• Piotr J Slomka, Ludovic Le Meunier, Sean W Hayes, Wanda Acampa, Muneo Oba, Gillian G Haemer, Daniel S Berman, and Guido Germano.
• Department of Imaging and Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA. Piotr.Slomka@cshs.org
• J. Nucl. Med. 2008 Dec 1; 49 (12): 1992-8.

UnlabelledCT-based attenuation correction (AC) for myocardial perfusion PET studies is challenging because of respiratory motion. Our study aimed to compare the transmission CT (TCT)-based and CT-based AC for myocardial perfusion PET/CT images with a direct semiquantitative approach comparing differences in segmental count distribution.MethodsStress and rest (82)Rb PET scans from 54 consecutive patients acquired on a PET/CT scanner with dual CT-based and TCT-based AC were considered. TCT- and CT-based AC images were automatically registered to each other, and direct voxel-based and American Heart Association segment-based estimation of positive and negative changes between these scans was performed. Additionally, visual quality control (QC) of CT map alignment with PET emission data was performed by 2 expert observers, and studies with significant (>/=5 mm) misalignment were reprocessed with corrected CT alignment.ResultsWe used the 17-segment American Heart Association model for TCT-to-CT regional change analysis in all patients and found that 4 segments on rest and 4 segments on stress scans differed more than 3% between CT- and TCT-corrected images for studies without significant misalignments (<5 mm); only 1 differed by more than 5%. In cases with significant misalignment of greater than or equal to 3% TCT-CT AC, changes were observed on 14 rest and 10 stress segments; after alignment, these differences were still seen in 13 rest segments and 11 stress segments. Visual QC revealed that 46% of rest and 54% of stress PET scans were misaligned by greater than or equal to 5 mm with the CT maps acquired during normal breathing. The range of the reported PET/CT misalignment was 0-15 mm in x, 0-16 mm in y, and 0-20 mm in z directions. The overall agreement in visual QC of PET/CT alignment between the observers was 72.2%ConclusionThere are significant differences between TCT and CT AC applied to cardiac PET/CT studies, which remain after alignment of CT maps to emission data.

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