Long vs. short axial field-of-view PET scanners for brain imaging: a phantom study

Long axial field-of-view (LAFOV) PET scanners offer substantially higher sensitivity compared to conventional short axial field-of-view (SAFOV) systems, potentially enabling reduced injected activity, shorter acquisition times, and improved signal-to-noise ratios in brain imaging. However, given the geometric differences between these systems, it is important to assess whether these differences impact image quality and quantitative accuracy before translating established SAFOV protocols to LAFOV systems. This study has two goals: (1) to compare image quality (IQ) metrics between a SAFOV PET scanner (Siemens Biograph Vision) and a LAFOV PET scanner (Siemens Biograph Vision Quadra) using a Hoffman brain phantom, and (2) to quantify the effective axial sensitivity gain provided by the LAFOV system for brain imaging.

Two phantom experiments were performed: the first assessed IQ metrics and the influence of external background activity, while the second evaluated brain-specific sensitivity at different axial positions within the LAFOV scanner.

Overall, IQ metrics were highly comparable between scanners and were minimally affected by external background activity. Positioning the phantom at the first detector ring of the LAFOV scanner yielded a 1.2-1.4 $\times$ sensitivity increase relative to the SAFOV system, whereas positioning it at the axial centre resulted in a sensitivity gain of up to 3.4 $\times$ .

These findings indicate that LAFOV PET systems maintain quantitative consistency with SAFOV scanners while offering higher sensitivity. This supports the development of optimized PET imaging protocols to reduce injected activity and radiation exposure, thereby improving safety and enabling broader inclusion of vulnerable populations in brain PET studies.