Design study of a practical-entire-torso PET (PET-PET) with low-cost detector designs

This is a design and Monte Carlo (MC) study of a practical entire torso PET (PET-PET) with 1-meter axial field-of-view (AFOV) for imaging the head-&-torso simultaneously. Our studies show that PET-PET would image the entire body in 2-3 minutes with a 3-4 mCi FDG injected dose, which would reduce whole-body cancer-imaging cost and the low dose may justify its use for cancer screening. It can capture dynamic whole-body time-activity and arterial input from the heart/aorta to create quantitative metabolic rate-constant images of the entire body. It uses low-cost BGO crystals with/without depth-of-interaction (DOI) detection. In the DOI implementations, a sparse quadrant-sharing SiPM readout design is used to reduce SiPM related cost, thus enabling the cost to approach that of current clinical PET with LYSO in a 25-cm AFOV. The Dichotomous Offset-Quadrant-Sharing (DO-QS) DOI detector design has a crystal-to-SiPM ratio of 2:1; it has unique crystal-column decoding (X-Y) without analog-decoding errors. The DOI detector would improve the transaxial radial resolution and may also improve the axial resolution. The non-DOI detector design uses 4 SiPM (3-mm) at the four corners of a 5×5 (6×6) BGO array to achieve a crystal-to-SiPM ratio of 6.25:1 (9:1); it uses mirror film of difference sizes and shapes between crystals to distribute scintillation light for analog crystal decoding. For the DO-QS DOI detector design, MC studies showed DOI resolution of 5 mm with each 3.24×3.24×20 mm³ BGO pixel columns divided into 4-layers along the 20-mm depth; the time resolution (FWHM) is 1.6 ns. Resolution and NES were estimated with MC simulations for point sources and extended whole-body Turkington phantom (extended to 80-cm in axial length), which showed the transaxial resolution to be 2.8 to 3.3 mm (DO-QS). The NES result showed 2-3 minutes whole-body imaging with 3-4 mCi FDG injection would be comparable to current clinical PET with 10-mCi injection and 20-min imaging.