Performance of digital silicon photomultipliers for time of flight PET scanners

The performance of Digital Silicon Photomultipliers (dSiPM) coupled to a LYSO array containing 15×15 pixels with a size of 2×2×22 mm3 is evaluated to determinate their potential for whole body Time of Flight (TOF) PET scanners. The detector pixels are smaller in size than the light sensors and therefore light spreading is required to determine the crystal where interaction occurred. A light guide of 1 mm was used to spread the light and neighbor logic (NL) configuration were employed to ensure correct crystals identification. We studied the energy resolution and coincidence resolving time (CRT) for different trigger levels. The measured average energy resolution across detector was 14.5 %. Prior to measurements of time resolution skew time calibration of dSiPM was performed. The average CRT achieved using trigger level 1 option was 376 ps FWHM. Finally, we studied the amount of events that are disregarded due to dark count effects for different trigger levels and temperatures. Our studies show that a trade-off must be made between the detector’s CRT and sensitivity due to its vulnerability to dark counts. To employ dSiPM in TOF PET systems without 1:1 coupling effective cooling is necessary to limit dark count influence

Determination of the resolution limit of a whole body PET scanner using monte carlo simulations

We studied the resolution limit that can be obtained for a whole body PET scanner. The results were obtained using a Monte Carlo based simulation program. The influence of two parameters was investigated: the crystal pixel size and the number of layers used for Depth-Of-Interaction (DOI) correction

Influence of detector pixel size, TOF resolution and DOI on image quality in MR-compatible whole-body PET

The optimization of a whole-body PET system remains a challenging task, as the imaging performance is influenced by a complex interaction of different design parameters. However, it is not always clear which parameters have the largest impact on image quality and are most eligible for optimization. To determine this, we need to be able to assess their influence on image quality. We performed Monte-Carlo simulations of a whole-body PET scanner to predict the influence on image quality of three detector parameters: the TOF resolution, the transverse pixel size and depth-of-interaction (DOI)-correction. The inner diameter of the PET scanner was 65 cm, small enough to allow physical integration into a simultaneous PET-MR system. Point sources were used to evaluate the influence of transverse pixel size and DOI-correction on spatial resolution as function of radial distance. To evaluate the influence on contrast recovery and pixel noise a cylindrical phantom of 35 cm diameter was used, representing a large patient. The phantom contained multiple hot lesions with 5 mm diameter. These lesions were placed at radial distances of 50, 100 and 150 mm from the center of the field-of-view, to be able to study the effects at different radial positions. The non-prewhitening (NPW) observer was used for objective analysis of the detectability of the hot lesions in the cylindrical phantom. Based on this analysis the NPW-SNR was used to quantify the relative improvements in image quality due to changes of the variable detector parameters. The image quality of a whole-body PET scanner can be improved significantly by reducing the transverse pixel size from 4 to 2.6 mm and improving the TOF resolution from 600 to 400 ps and further from 400 to 200 ps. Compared to pixel size, the TOF resolution has the larger potential to increase image quality for the simulated phantom. The introduction of two layer DOI-correction only leads to a modest improvement for the spheres at radial distance of 150 mm from the center of the transaxial FOV