Region-based Efficiency Correction for the High-Resolution quad-HIDAC PET scanner

The very high resolution quad-HIDAC PET scanner has four detector banks each with four planar high density avalanche chambers, capable of collecting billions of lines-of-response (LORs), with very high spatial resolution, good absolute sensitivity and a large field of view (170 mm times 170 mm times 280 mm). However, it is crucial to correct for degrading factors introduced by the scanner´s geometry and detection. A plane converter efficiency estimation method based on acceptance regions is presented, in which it is possible to represent a plane converter as a set of detection efficiency areas. LORs registered in a particular region in coincidence with another in the opposite plane converter are registered in a square array named a cooccurrence matrix, which is the basis of the method. The reciprocal of these factors are used as a multiplicative correction within the list-mode EM algorithm, event by event. A methodology to obtain the system-geometric correction factors is described and included within the reconstruction process as a normalisation component. Reconstructed images from a uniform ¹⁸F cylinder source (3 cm diameter, 5 cm length) and a ⁶⁸Ge line source (15.5 cm length), were used to assess the region-efficiency and system-geometry correction.