EARL compliance of the Biograph One PET/MR using (contrast) recovery coefficients

Background The new Siemens Biograph One PET/MR scanner (<195 ps ToF) is assessed using EANM EARL accreditation with/without a background-corrected recovery coefficient. Methods The [ 18 F]FDG-filled NEMA image quality (IQ) phantom was scanned with a 9.2:1 sphere-to-background activity concentration ratio with varying axial positions from 0 to 12 cm off-centre, a scan duration from 30 to 600 seconds, a number of iterations from 2 to 8, at voxel size 1.6 or 3.2 mm and Gaussian postfiltering from 0 to 7 mm FWHM. We reconstructed offline with a CT-based μ-map without (EARL1) and with PSF-modelling (EARL2). Assessment was done with the EANM EARL tool comparing recovery coefficients (RC) without background correction and contrast recovery coefficients (CRC). Results The Biograph One is EARL1 and EARL2 compliant with 6-7 mm and 4 mm filtering, respectively, and standard reconstruction parameters. Filtering is the only parameter with a major impact on RC/CRC. Calibration factors are 1.0-0.95 and the scanner has low noise across parameters with coefficients of variation (CoV) above 7.5% at only four settings: EARL1 with no filtering, EARL2 (2 mm filtering) at a 30- or 60-second scan duration or 8 iterations. Conclusion The Biograph One is EARL1 and EARL2 compliant. The introduction of CRC in EARL offers calibration and background independent contrast recovery evaluation, with no larger shift in results. One small but significant change is that the Biograph One was EARL2-compliant with CRC (at 4 mm filtering and standard parameters) but was not EARL2 compliant when using RC. By the planned change from RC to CRC EARL accreditation has become more robust in case of an off-target absolute calibration or activity measurement/phantom filling deviations.