Full field spatially-variant image-based resolution modelling reconstruction for the HRRT

Accurate characterisation of the point spread function across the entire field of view is crucial in order to account for spatially dependent factors that degrade the resolution of the reconstructed images. The HRRT users community resolution modelling reconstruction software includes a shift-invariant resolution kernel, which leads to transaxially non-uniform resolution recovery. In this work we have developed a spatially-variant image-based resolution modelling reconstruction dedicated to the HRRT scanner, using an experimentally measured shift-variant resolution kernel. Application of the newly developed resolution modelling reconstruction on both phantom and clinical data demonstrated improvements both in contrast and resolution recovery, particularly for those regions that are close to the edges of the field of view, with almost uniform resolution recovery across the entire transverse field of view. In addition, because the newly measured resolution kernel is slightly broader with wider tails, compared to the deliberately conservative kernel employed in the HRRT users community software, the reconstructed images appear to have not only improved contrast recovery, but also better noise characteristics, at the expense of minor development of ringing (i.e. Gibbs) artefacts.