Multicenter quantitative (18)F-fluorodeoxyglucose positron emission tomography performance harmonization: use of hottest voxels towards more robust quantification

BACKGROUND: Harmonization methods reduce variability between different make and models of positron emission tomography (PET) scanners. The study aims to explore harmonization strategies that lead to comparable and robust quantitative metrics in a multicenter setting. METHODS: NEMA IEC Phantom data acquisition was performed for low and high spheres-to-background ratios (SBR4:1 and 10:1) on six PET/CT (computed tomography) scanners. Different reconstruction sets, including the number of sub-iterations, number of subsets, and full width at half maximum (FWHM) for each scanner, were evaluated towards optimized and harmonized reconstruction settings. Recovery coefficients (RCs) of four quantitative metrics, including standardized uptake value (SUV)(max), SUV(ISO-50) (SUV(mean) in 50% isocontour), SUV(peak), and mean uptake of 10 highest concentration voxels were evaluated as RC(max), RC(ISO-50), RC(peak), and RC(10V), representing percent difference relative to the static ground truth case as functions of sphere sizes. A set of image reconstruction parameters was proposed for harmonized reconstruction to minimize variability between scanners. The root mean square error (RMSE), curvature, and reproducibility were examined. The proposed reconstruction protocols for harmonization and standard clinical reconstruction settings were compared to each other across all scanners. RESULTS: A significant difference (P value <0.0001) was observed in the aforementioned quantitative metrics between SBR10 and SBR4. Reconstruction parameter sets with the smallest RMSE and RC values within 10% bias were identified as the best candidate for harmonization. The coefficient of variation of the mean value of RCs (CV(MRC)) shows a remarkable reduction of about 28%, 26%, 32%, and 19% in harmonized reconstruction settings for MRC(max), MRC(ISO-50), MRC(peak), and MRC(10V), respectively. CV(MRC) for MRC(10V) in the harmonized reconstruction setting was 5.9% in SBR4, while the smallest value in SBR10 belongs to MRC(peak,) with a value of 5.8%. The reproducibility of RC is improved by deriving the value from ten hottest voxels and is equally reproducible with RC(peak). Compared to RC(max) and RC(ISO-50), the variability is reduced by 18% and 22% if ten voxels are pooled. CONCLUSIONS: Harmonizing PET/CT systems with and without point spread function/time of flight (PSF/TOF) using various vendor-developed image reconstruction algorithms improves the quantification reproducibility. RC(10V), likewise RC(peak), is superior to the rest of the quantitative indices in terms of accuracy and reproducibility and helpful in quantifying lesion volume below 1 mL.