Background: Our aim was to determine sets of reconstruction parameters for the Biograph Vision Quadra (Siemens Healthineers) PET/CT system that result in quantitative images compliant with the European Association of Nuclear Medicine Research Ltd. (EARL) criteria. Using the Biograph Vision 600 (Siemens Healthineers) PET/CT technology but extending the axial field of view to 106 cm, gives the Vision Quadra currently an around fivefold higher sensitivity over the Vision 600 with otherwise comparable spatial resolution. Therefore, we also investigated how the number of incident positron decays - i.e. exposure - affects EARL compliance. This will allow estimating a minimal acquisition time or a minimal applied dose in clinical scans while retaining data comparability.
Methods: We measured activity recovery curves on a NEMA IEC body phantom filled with an aqueous 18 F solution and a sphere to background ratio of 10 to 1 according to the latest EARL guidelines. Reconstructing 3570 images with varying OSEM PSF iterations, post-reconstruction Gaussian filter full width at half maximum (FWHM), and varying exposure from 0.2 MDecays/ml (= 10 sec frame duration) to 59.2 MDecays/ml (= 1 h frame duration), allowed us to determine sets of parameters to achieve compliance with the current EARL 1 and EARL 2 standards. Recovery coefficients (RCs) were calculated for the metrics RC max , RC mean , and RC peak , and the respective recovery curves were analysed for monotonicity.
Results: Using 6 iterations, 5 subsets and 7.8 mm Gauss filtering resulted in best EARL 1 compliance and recovery curve monotonicity in all analysed frames. Most robust EARL2 compliance and monotonicity was achieved with 4 iterations, 5 subsets, and 4.6 mm Gauss FWHM in frames with durations between 10 min and 30 sec. RC peak only impeded EARL2 compliance in the 10 sec frame.
Conclusions: While EARL1 compliance proved to be robust over all exposure ranges, EARL2 compliance required exposures between 0.6 MDecays/ml to 11.5 MDecays/ml. The Biograph Vision Quadra’s high sensitivity makes frames as short as 10 sec feasible for comparable quantitative images. Lowering EARL2 RC max limits closer to unity would possibly even permit 10 sec EARL2 compliant frames.