The effect of reconstruction algorithms on semi-quantitative measurements in ¹⁸F-FDG PET/CT imaging

This study was carried out to understand whether Q.Clear and ordered subset expectation maximization (OSEM), reconstruction algorithms used in fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) applications, and parameters such as time of flight (TOF) and point spread function (PSF) cause different results in semi-quantitative measurements.

Raw PET data of 264 patients who were referred to ¹⁸F-FDG PET/CT imaging with the purpose of evaluation of known or suspicious malignant disease were reconstructed separately with Q.Clear (GE Healthcare), a BPL, an OSEM algorithm, PSF (SharpIR®) and TOF (VUE Point FX®) methods. Each patient's liver, mediastinal blood pool, metabolic tumor volume (MTV), total lesion glycolysis (TLG), and standardized uptake values (SUV) (SUVmax, SUVmean, and SUVpeak) of a total of 264 lesions selected from the patients were performed.

β350+ToF yielded higher measurement results than all other variables for all of the lesion SUVmax, lesion SUVmean, L/AP SUVmax, and L/AP SUVmean parameters. OSEM+ToF and OSEM+TOF+PSF algorithms yielded higher mean and median SUVmax values for the reference structures (liver and mediastinum) and for lesions SUVmax and SUVmean values were statistically significantly lower than the β350+ToF method. The method with the lowest mean value for the L/Liver SUVmax variable was OSEM+ToF 4iter16ss (mean=1.76), while the method with the highest mean value was β350+ToF (mean=2.26). β350+ToF was the reconstruction method with the highest ratios for L/AP SUVmax and SUVmean for both lesions below and above 1 cm. β350+ToF algorithm had also statistically significantly higher results for these variables compared to all other parameters in malignant lesions.

When comparing ¹⁸F-FDG PET/CT images, the use of different reconstruction algorithms may lead to misleading results, especially in the evaluation of response to treatment of malignancies.