Comparison of template-guided and calculated attenuation corrections in FDG brain PET imaging

Objectives Template guided attenuation correction (TGAC) that does not require transmission PET data would be possible solution for AC in integrated PET/MR system. In this study, we evaluated the compatibility of the TGAC using statistical probabilistic anatomic map (SPAM) which is an atlas-based volume of interest (VOI).

Methods Siemens ECAT 47 PET was used. FDG brain PET of 16 normal controls were retrospectively analyzed. Attenuation map (μ map) template in SPM5 was used for the AC. Individual emission (EM) data was spatially normalized onto MNI template, and inverse transformations of the μ map template into the individual space were performed to obtain the template guided μ map for individual data sets. Transformed μ maps were then forward projected to generate the AC factors. TGAC was compared with segmented (SAC), calculated (CAC) method. SPAM images of 98 VOIs were used to objectively calculate the PET counts in the cerebral cortical, cerebellar, and subcortical VOIs. Regional mean pixel value in each VOI was calculated and normalized to the mean count of the whole brain.

Results TGAC was compatible with SAC. TGAC showed a strong correlation (R²=0.96) with SAC, and the regression line had almost a unit slope and no bias (y=0.99x). By contrast, the pairs of CAC and SAC data showed a much scattered distribution (y=0.96x+0.02) (R²=0.86).

Conclusions The TGAC was reliable in FDG brain PET studies in terms of compatibility with the SAC. The μ-map could be derived from the EM PET data. Therefore, the TGAC method could be useful AC option for the integrated PET/MR system.