Parameters Optimization of Volumetric Reconstruction Technique for L-SPECT Imaging

摘要

Light field SPECT (L-SPECT) is an improved version of SPECT and works by introducing the concept of plenoptic imaging to reduce scanning time and to increase the amount of detected information. In L-SPECT, a tungsten pinhole array is used as a collimator to differentiate the incoming direction of radiation, rather than only allowing radiation from a set direction dictated by a conventional tube collimator. The distance of the pinhole array to the sensors' plane is so that the sensors behind each pinhole are only exposed through that pinhole alone. This paper investigates the effects of the pinholes' diameter and pitch over the reconstruction resolution using simulation experiments. In this proposed reconstruction algorithm, a ray is back projected from the centre of each detector with non-zero pixel value via the corresponding pinhole's centre, and towards the area of interest with 128×128×128 voxels. The projected rays' intersections are identified by using ray tracing and the voxels at which they intersect are updated by incrementing with the sum of the pixel values from each detector involved. Experiments are conducted with pinhole arrays of 100×100, 50×50, 30×30 and pinhole diameter of 0.5mm, 1mm and 2mm. Reconstruction is conducted for various simulated objects. Results indicate that when the number of pinholes is increased, the diameter of the pinholes should be reduced to maintain spatial resolution. Moreover, a reconstruction performed by using only 12 projections shows similar quality for the same with 36 and 72 projections. The analysis of the proposed reconstruction algorithm shows that it improves spatial resolution over the filtered back projection algorithm. Reconstruction quality can be further improved by considering scattering loss and photon attenuation.