Virtual scanner geometry for iterative 3D PET reconstruction adaptable to complex and irregular scanner topologies

We have developed a new method to transform any kind of 3D PET scanner data to a regular cylinder structure which consists of virtual crystals arranged in regular rings without any gaps. In this way, the 3D projection data can be stored without introducing geometrical mismatches with respect to the assigned projectors of the iterative reconstruction. In addition, the physical crystal sizes of the scanner can be taken into account during the data conversion procedure. The conversion of all measured Lines-of-Response (LOR) to a virtual, regular cylinder geometry allows to formalise the geometrical transcription while simultaneously minimising the loss of information, e.g. arc corrections can be omitted completely. Finally, the regularity of the converted projection data allows a very fast and accurate implementation of the reconstruction algorithm which is based on a memory-resident compressed system response matrix. The geometrical accuracy of the applied projectors depends only on the user-defined granularity of the virtual geometry which can be adjusted as a compromise between operating expense and precision. The ClearPET Neuro Scanner [2] with its rotating gantry and the crystal double-layer design has been used for a first application of the new universal 3D reconstruction technique. The presented results indicate the high potential of the new conversion method in terms of achievable contrast-noise ratio and resolution.