The importance of correction for tissue fraction effects in lung PET: Preliminary findings

Purpose: It has recently been recognized that PET/CT may play a role in diffuse parenchymal lung disease. However, interpretation can be confounded due to the variability in lung density both within and between individuals. To address this issue a novel correction method is proposed. Methods: A CT scan acquired during shallow breathing is registered to a PET study and smoothed so as to match the PET resolution. This is used to derive voxel-based tissue fraction correction factors for the individual. The method was evaluated in a lung phantom study in which the lung was simulated by a Styrofoam/water mixture. The method was further evaluated using 18F-FDG in 12 subjects free from pulmonary disease where ranges before and after correction were considered. Results:Correction resulted in similar activity concentrations for the lung and background regions, consistent with the experimental phantom set-up. Correction resulted in reduced inter-and intrasubject variability in the estimated SUV. The possible application of the method was further demonstrated in five subjects with interstitial lung changes where increased SUV was demonstrated. Single study preand post-treatment studies were also analysed to further illustrate the utility of the method. Conclusion: The proposed tissue fraction correction method is a promising technique to account for variability of density in interpreting lung PET studies.