Phantom-based comparison of image quality in two digital PET/CT systems with different axial fields of view

Objective.Silicon photomultiplier (SiPM)-based positron emission tomography (PET)/ computed tomography (CT) scanners offer enhanced sensitivity and timing resolution compared with conventional detector designs. This study compared two SiPM PET/CT systems sharing the same technology platform but differing in axial field of view (AFOV) and system sensitivity, to evaluate their impact on image quality, lesion detectability, and partial-volume effects.Approach.A flangeless Esser PET phantom, filled with gallium-68 [⁶⁸Ga] and containing hot cylinders (8-25 mm) and cold spheres (9.5-31.8 mm), was imaged on both systems. Acquisitions employed matched reconstruction protocols. The shorter AFOV system used a 5 minute scan, while the longer AFOV system used a 2.5 minute scan to assess performance under reduced acquisition time. Image quality was quantified using contrast recovery coefficient (CRC), contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR).Main results.The longer AFOV system exhibited higher CRC and SNR for medium-to-large hot cylinders despite the shorter acquisition (16 mm cylinder CRC: 53.18 vs 88.12; SNR: 4.11 vs 7.14; 25 mm cylinder CRC: 84.30 vs 92.42; SNR: 17.99 vs 30.08 for shorter vs longer AFOV systems). The shorter AFOV system performed better for the smallest hot cylinder (8 mm; CRC: 73.79 vs 64.09; CNR: 343.98 vs 258.99) and consistently achieved higher CRC and CNR for cold spheres, particularly at smaller diameters.Significance.The longer AFOV system provides superior contrast recovery and noise performance for medium-to-large lesions, even with reduced scan duration. Conversely, the shorter AFOV system offers advantages for very small hot and cold targets, illustrating the trade-off between sensitivity and spatial resolution. These system-specific characteristics should guide protocol optimization for different clinical imaging tasks.