Abstract
BACKGROUND: The adoption of silicon photomultiplier (SiPM) detectors over conventional photomultiplier tubes (PMTs) in Positron Emission Tomography (PET) has enhanced overall system performance. In this phantom study, small-lesion detectability was assessed for SiPM-based and PMT-based PET systems for various inhomogeneity sizes, acquisition times and activity contrasts between the inhomogeneity and background. METHODS: Six spheres of internal diameters ranging between 4.0 mm and 13.0 mm were integrated into a NEMA/IEC PET Body Phantom and filled with fluorodeoxyglucose, with a sphere activity concentration of 29.2 MBq/L and five sphere-to-background activity concentration ratios between 4 and 20. Scans were performed with an SiPM-based system and a PMT-based PET system for each sphere-to-background activity concentration ratio for acquisition times between 1 and 10 min, and image reconstruction was performed with QClear for both systems. Reconstructed images were evaluated for lesion detectability by a lesion detectability index, contrast-to-noise ratio and lesion detectability Likert scales with validation by comparison with the Rose criterion. A model to estimate the acquisition time for each sphere to be detectable was derived and acquisition time was compared. RESULTS: The SiPM-based system demonstrated superior lesion detectability, identifying smaller and less active spheres with shorter acquisition times. For a sphere-to-background activity concentration ratio of 10 and a sphere internal diameter of 6.2 mm, the SiPM-based system achieved a contrast-to-noise ratio of 15.8 and a lesion detectability Likert score of 3, compared to 12.0 and 2, respectively, for the PMT-based system. The acquisition time of the SiPM-based system could be reduced by between 1.6% and 89%, depending on sphere size and sphere-to-background activity concentration ratio. The minimum CNR required for a sphere to achieve a detectability Likert score of 0.5 was 6.3, consistent with the Rose criterion. CONCLUSION: SiPM-based PET has enhanced lesion detectability, especially for smaller, less active regions and for shorter acquisition times. A five-point Likert scale is an effective measure of lesion detectability. Guidance is also provided for choosing the acquisition time as a function of lesion size and activity uptake, and for changes in image quality testing protocols.