Shared-photodetector readout to improve the sensitivity of positron emission tomography

Abstract

Sensitivity is an important performance characteristic of positron emission tomography (PET) systems. Improved sensitivity can be used to reduce injected dose, reduce scan time, or improve the signal-to-noise ratio and temporal resolution for dynamic studies. One way to improve the sensitivity of PET scanners is to reduce the gaps between detector modules. In this paper, a new signal processing method, named the shared-photodetector readout method, is proposed and evaluated. In this method, the signals generated in nearest neighbor photodetectors adjacent to the detector module of interest, were used to help identify the interaction location in the detector module of interest. Using this method, scintillator array-based detector modules with almost 100% packing fraction can be built, and the edge crystals can be clearly resolved, even when the crystals are small compared to the photodetector size. To evaluate this signal processing concept in one dimension, a detector block with four dual-ended readout detector modules, was designed. The detector block consisted of eight 4 × 4 arrays of SensL MicroFJ-30035 SiPMs coupled to both ends of a 14 × 56 array of 0.9 × 0.9 × 20 mm LYSO elements with a pitch size of 0.96 mm and a length of 20 mm. Performance in terms of energy resolution, flood histogram, timing resolution and depth-of-interaction resolution obtained using the shared-photodetector readout method were compared to those obtained using a conventional readout method. The results show that better over-all performance was achieved using the shared-photodetector readout method, especially at the edges and corners of the array.

Ultra‐high‐resolution depth‐encoding small animal PET detectors: Using GAGG and LYSO crystal arrays

“…In order to resolve all the crystals of the detector, either a smaller crystal array or a more complicated readout method using light and signal sharing among neighboring detectors needs to be used. 49 This study demonstrated that both GAGG and LYSO arrays with small crystal cross-sections (0.4 × 0.4 mm 2 and 0.3 × 0.3 mm 2 ) and a long length (20 mm) can be manufactured. Detector 1 showed a poor uniformity of photopeak amplitudes because the GAGG material bought from the first company was not enough to make the array and hence ∼30% of the GAGG material was procured from a substitute company.…”

“…For the two detectors with a crystal of 0.4 × 0.4 × 20 mm 3 size and a scintillator array which has almost the same end area as the area of the SiPM array, all but the three rows and three columns of the edge crystals can be clearly resolved. In order to resolve all the crystals of the detector, either a smaller crystal array or a more complicated readout method using light and signal sharing among neighboring detectors needs to be used 49 …”

“…The active area of the SiPM array was 17.8 × 17.8 mm 2 , which was close to the end area of crystal arrays 1 and 2 (17.6 × 17.6 mm 2 ). A signal multiplexing circuit as shown in Figure 2, was used to convert the 64 signals of a SiPM array into four position‐encoding energy signals 49 . The 64 signals of a SiPM array were first summed to obtain eight row and eight column signals.…”

“…The detailed information of the four crystal arrays is shown in Table 1 A signal multiplexing circuit as shown in Figure 2, was used to convert the 64 signals of a SiPM array into four position-encoding energy signals. 49 The 64 signals of a SiPM array were first summed to obtain eight row and eight column signals. The row and column signals were then connected to one-dimensional position-encoding circuits that weighed all signals using resistors with resistance values as shown in Figure 2.…”

Technical opportunities and challenges in developing total-body PET scanners for mice and rats

“…The spatial resolution obtained using the MLEM reconstruction algorithm is ~ 0.5 mm across the mouse/rat bodies. The UHS-PET scanner is based on our recently developed curved LYSO arrays with a 1.0 mm pitch size on the inner side and 30 mm thickness [ 22 , 66 ]. The curved LYSO arrays were developed to reduce the dead space between detector modules in PET scanners with conventional cuboid scintillator arrays, and thereby the sensitivity can be significantly improved (Fig.…”