Using EQ·PET to reduce reconstruction-dependent variations in [ 18 F]FDG-PET brain imaging.

This study aims at assessing whether EANM harmonisation strategy combined with EQ PET methodology could be successfully applied to harmonize brain 2-deoxy-2[F-18]fluoro-D-glucose ([F-18]FDG) positron emission tomography (PET) images. The NEMA NU 2 body phantom was prepared according to the EANM guidelines with an [F-18]FDG solution. Raw PET phantom data were reconstructed with three different reconstruction protocols frequently used in clinical PET brain imaging: (R-1) Ordered subset expectation maximization (OSEM) 3D with time of flight (TOF), 2 iterations and 21 subsets; (R-2) OSEM 3D with TOF, 6 iterations and 21 subsets; and (R-3) OSEM 3D with TOF, point spread function (PSF), and 8 iterations and 21 subsets. EQ PET filters were computed as the Gaussian smoothing that best independently aligned the recovery coefficients (RCs) of reconstructions R-2 and R-3 with the RCs of the reference reconstruction, R-1. The performance of the EQ.PET filter to reduce variations in quantification due to differences in reconstruction was investigated using clinical PET brain images of 35 early-onset Alzheimer's disease (EOAD) patients. Qualitative assessments and multiple quantitative metrics on the cortical surface at different scale levels with or without partial volume effect correction were evaluated on the [F-18]FDG brain data before and after application of the EQ.PET filter. The EQ PET methodology succeeded in finding the optimal smoothing that minimised root- mean-square error (RMSE) calculated using human brain [F-18]FDG-PET datasets of EOAD patients, providing harmonized comparisons in the neurological context. Performance was superior for TOF than for TOF + PSF reconstructions. Results showed the capability of the EQ.PET methodology to minimize reconstruction-induced variabilities between brain [F-18]FDG-PET images. However, moderate variabilities remained after harmonizing PSF reconstructions with standard non-PSF OSEM reconstructions, suggesting that precautions should be taken when using PSF modelling.