Simulation guided optimization of Dual Layer Offset detector design for use in small animal PET

A small animal PET insert for use inside of a small MR bore is currently in the design phase. The small diameter of the tomograph results in an increased need to collect Depth of Interaction (DOI) information to mitigate the parallax error. The tomograph will use a Dual Layer Offset block design to collect DOI information. Of critical importance to the design of the block is the depth into the block where the front layer is separated from the back layer. With the total thickness of scintillating crystal limited to 10 mm, GATE simulations with a single block were run with the front layer thickness ranging from 1 mm to 10 mm (single layer). These simulations characterized the block´s ability to accurately locate the radial coordinate of the first interaction location of a `single´. It was found that a split between front and back that is roughly even minimized the mispositioning of the radial coordinate of first interaction. To estimate the reconstructed resolution and resolution uniformity obtainable with this block design, coincidence data from a full tomograph were simulated. Data were reconstructed using Filtered Back Projection. Data were also reconstructed with the DOI information discarded to estimate the improvement in resolution uniformity obtained with this block design.