A sinogram resolution modelling adapted to the geometry of the HRRT

A sinogram resolution modelling reconstructing technique adapted to the geometry of the High Resolution Research Tomograph (HRRT) was developed and tested. The proposed reconstruction approach permits the incorporation of the effects of the inter-crystal penetration into the reconstruction process. It takes into account the incidence angles (α angles) formed by the intersection of the Line Of Response (LOR) with the detector heads. Event generated by annihilation photons that penetrate with non-normal incidence angles leads to the degradation of the resolution. When the scanner geometry is polygonal, like HRRT, annihilation photons penetrate with oblique a angles independently of the radial position. Another consequence of the octagonal geometry of the HRRT is the fact that the two incidence angles formed by the intersection of each LOR with the detector heads are not always equal. Three different possible relations between these angles can be found, and thereby the sinogram can be decomposed into 3 distinct regions (α Regions). A spatially varying asymmetric Gaussian function was used to model this blurring effect in the radial and axial directions. The estimation of the radial blurring kernel was done based in a line source measurement. This kernel was used in the reconstruction of a point source data acquired at different radial distances. The resulting images were compared with images obtained by reconstruct the datasets without resolution modelling and with resolution modelling in the image space. The results indicate that, relative to the other two reconstructions, the proposed method improves the resolution and achieves a more uniform radial resolution.