Digital vs Analog: PET/CT Spatial Resolution

Objectives: The objective of this study is to determine and compare the spatial resolution of digital and analog PET/CT systems by constructing a National Electrical Manufacturers Association (NEMA) phantom. The NEMA NU2-07 prototype was used to analyze the point spread function and Full Width at Half Maximum (FWHM) of the two machines to determine the overall resolution when comparing the two systems.

Methods: Using the NEMA NU2-07 prototype, three capillary tubes were filled with 5mCi/mL of F-18-FDG in order to compare spatial resolution between analog and digital systems. PET/CT whole body scans were acquired using three bed positions on both the Siemens Biograph mCT Flow (analog) and Philips Vereos PET/CT (digital) at two separate institutions. The point spread function was analyzed by measuring the count density of the points and the images were exported in order to compare the FWHM peaks of the two systems.

Results: The Full Width at Half Maximum was calculated by viewing the transverse image and measuring the counts horizontally across the image for both systems. The voxel size was calculated by dividing the field of view by the matrix size of each system. The field of view and matrix size used for the analog system was 700mm and 512X512 respectively. The field of view and matrix size used for the digital system was 576mm and 576X576 respectively. The voxel size for the analog system was 1.37mm and 1mm for the digital system. The Full Width at Half Maximum for the analog system was 4.4mm and 4.16mm for the digital system.

Conclusions: Overall, the spatial resolution of both systems is similar. This was not a 1:1 comparison due to the difference in fields of views and matrix choices. We could not match the voxel size exactly, the voxel size of the analog system was wider, which is why the analog system had a larger Full Width at Half Maximum. This was the closest comparison possible between the Siemens Biograph mCT Flow and Philips Vereos PET/CT using the NEMA NU2-07 prototype.