Design Considerations for AMPET: The Ambulatory Micro-Dose, Wearable PET Brain Imager

Objectives As part of the BRAIN initiative, we are designing a mobile molecular brain imager that can be used on healthy subjects to study the functioning of the human brain during motion. The Ambulatory Micro-Dose, Wearable PET Brain Imager (AMPET) must be as light as possible while still providing adequate sensitativity and resolution. We report here on initial simulations studies to quantify the AMPET design trade-offs.

Methods We used the PET simulation system SimSET to model effects of AMPET design. Although SimSET provides fast and accurate simulations, it is limited to cylindrical volumes and surfaces for PET scanners. We added a new processing layer wherein an outer 'virtual target' cylinder is used to capture all potential annihiliation photon detection events. These events are then projected back to the AMPET detector surface, which is modelled as a truncated hemisphere. After verification we evaluated the relative coicidence efficiency of three designs for AMPET (radius 12 cm, axial extent of truncated hemisphere of 4 6 and 8 cm, no confounding effects, 100,000 decays). For input we used the 3D Hoffman brain digital reference object (DRO). The DRO mimics 18F-FDG uptake in normal brain, but can be modified to represent uptake of other neuro radiotracers.

Results The new approach of simulation of non-cylindrical scanners was verified. Using this approach the base efficiency of the AMPET designs were estimated. Doubling the axial extent of truncated hemisphere from 4 to 8 cm would more than triple the coincidence effeciency (3.5% to 11.4%), but would also double the weight, unless detector thickness is reduced.

Conclusions Using simulations of non-cylindrical scanners using the 3D Hoffman brain digital reference object (DRO), we are able to evaluate the performance and design trade-offs for AMPET to optimze the trade-offs between mobility, sensitivity, and resolution.

Research Support Suporrted by grant R24 MH106057