3D geometric normalization for the high resolution quad-HIDAC PET scanner

The high sensitivity, high resolution, quad-HIDAC PET scanner consists of 4 main detector banks which each contain either 4 or 8 detector modules, with 2 converter planes in each module. Coincidences are collected between opposite detector banks only, and not all lines of response (LORs) which are measurable by the system pass through the same number of detector planes, due to the finite axial extent of the stack of detector planes. Therefore, in order to utilize all the acquired data, it is necessary to account for this sensitivity variation for the system LORs. Existing reconstruction methods for the quad-HIDAC have not accounted for this, resulting in typically ∼14% of the data being rejected in the 16-module quad-HIDAC and ∼24% being rejected in the 32-module quad-HIDAC. This work presents the sensitivity calculation which is necessary to compensate for under-sampled LORs, by evaluating the solid angle as a function of position throughout the field of view - which gives rise to a correction scheme for incorporation into iterative list-mode reconstruction algorithms. This allows all the acquired data to be used in the image reconstruction process.