Nicholas Leybourne

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. 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. 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. 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.

Positron emission tomography (PET) is a widely used imaging modality for the diagnosis and treatment of oncologic diseases. In this study, we evaluated the performance of digital PET/CT systems using subcentimeter microsphere inserts in a NEMA IEC Body Phantom. The digital system was compared with a non-digital PET scanner using the same image reconstruction method. Results revealed that the digital system maintained higher detectability for smaller spheres with an average of 1 Likert score higher for lesions under 7.9 mm, indicating its ability to detect smaller lesions more effectively than the non-digital system. Furthermore, we observed that the drop-off in contrast recovery occurs at smaller microspheres in the digital PET system compared with that for a non-digital PET scanner. This suggests that digital PET may require the use of smaller spheres in image quality testing to ensure accurate comparison of performance between digital systems. This implies that digital systems can more accurately and effectively distinguish subtle differences in image intensity and spatial distributions of intensity, leading to improved lesion visibility and detection, which is likely due to the superior imaging characteristics offered by underlying detection technology.

Increased accessibility and recent developments in positron emission tomography (PET) detector technology have enhanced PET's role in radiotherapy treatment planning. This study investigates the efficacy of silicon photomultiplier (SiPM) PET systems for improving volume delineation. The study used a modified NEMA IEC Body Phantom filled with fluorodeoxyglucose (F-18-FDG) imaged using both a digital SiPM-based PET scanner and a non-digital, photomultiplier tube PET scanner. Results show distinct differences in target volumes determined using the two systems, with the digital system consistently demonstrating larger delineated target volumes between 1.91 - 3.56 times larger than that of the non-digital system. Target volumes delineated by the digital system were more reflective of the true geometric volume of the spheres with a range between 440 mm(3) and 984 mm(3) versus 209 mm(3) and 419 mm(3) for the non-digital system compared to the geometric volume of the spheres which was 2156 mm(3). This was most pronounced for higher sphere-to-background activity concentration ratios and smaller structures. This study suggests that digital PET allows for better selection of appropriate cancer treatment and could offer benefits for targeted radiation therapy.