EARL compliance of the Biograph Vision Quadra PET/CT

Introduction: Compliance of the long axial field of view (LAFOV) Siemens Biograph Vision Quadra PET/CT system to European Association of Nuclear Medicine Research Ltd. (EARL) standards 1 and 2 was explored to assess whether this scanner can adhere to European PET image harmonization guidelines for ¹⁸F-FDG tumor imaging. As current EARL guidelines were developed for conventional PET/CT systems with an axial field of view of approximately 20 cm, additional activity concentration recovery was evaluated at various locations throughout the LAFOV of 106 cm. In addition, several shorter scan times were explored to provide insight in image quality and quantitative accuracy at reduced scan durations.

Methods: Phantom measurements were performed using the NEMA NU2-2001 image quality phantom. This phantom was filled with a sphere-to-background ratio of 10:1 and placed at various positions within the LAFOV, i.e. at the center, and at one-eighth, a quarter, three-quarters, and seven-eighths of the axial FOV. List-mode PET data were acquired for 7 minutes per position. Subsequently, PET data were reconstructed using several shorter scan times, i.e. 15, 60, 120 and 240 s. Images were reconstructed using a Poisson ordered-subset expectation maximization (OP-OSEM) 3-dimensional (3D) iterative algorithm with 4 iterations, 5 subsets, a matrix size of 220x220 with a voxel size of 3.3x3.3x1.5 mm), application of time of flight (ToF), resolution modelling (PSF), and different Gaussian filters to comply with EARL standards 1 and/or 2. For each image, max, mean, and peak activity concentration recovery coefficients (RC) were derived for all spheres and compared with EARL standards specifications.

Results: EARL standards 1 compliance was achieved for all positions throughout the LAFOV using a 7 mm Gaussian filter for scan durations of 60, 120, 240 and 420 s. However, RCs were close to or on top of the specified upper limits. EARL standards 2 compliance was achieved for all positions throughout the LAFOV using a 5 mm Gaussian filter for all scan durations of 60, 120, 240 and 420 s, and all RCs were in the middle between specified upper and lower limits. Figure 1 shows recovery coefficients obtained from images acquired in the center of the FOV at 420 s scan duration. For both EARL1 and 2 standards reconstructions minimal variability (<7% for SUVmax, <3% for both SUVpeak and SUVmean) of RCs was observed between the positions tested along the axial FOV.

Conclusions: Images obtained using the LAFOV Siemens Biograph Vision Quadra PET/CT comply with EARL standards 1 and 2 specifications when using 3D ToF OP-OSEM with 4 iterations and 5 subsets, a matrix size of 220x220, resolution modelling, and Gaussian filtering of 7 and 5 mm, respectively. Improved performance characteristics of this LAFOV PET/CT scanner cause RCs to fit the lower and upper limits of EARL standards 2 guidelines better than EARL standards 1 guidelines. Therefore, it is recommended to use EARL standards 2 for image quantification and harmonization when using the Biograph Vision Quadra PET/CT. The results of these EARL quality control measurements also suggest that it should be possible to substantially lower radioactivity concentrations and/or reduce scan durations as compared with current clinical systems in case of EARL 2 standards reconstructions.

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