Lutetium oxyorthosilicate block detector readout by avalanche photodiode arrays for high resolution animal PET

Abstract

Avalanche photodiodes (APDs) have proven to be useful as light detectors for high resolution positron emission tomography (PET). Their compactness makes these devices excellent candidates for replacing bulky photomultiplier tubes (PMTs) in PET systems where space limitations are an issue. The readout of densely packed, 10 x 10 lutetium oxyorthosilicate (LSO) block detectors (crystal size 2.0 x 2.0 x 12 mm3) with custom-built monolithic 3 x 3 APD arrays was investigated. The APDs had a 5 x 5 mm2 active surface and were arranged on a 6.25 mm pitch. The dead space on the edges of the array was 1.25 mm. The APDs were operated at a bias voltage of approximately 380 V for a gain of 100 and a dark current of 10 nA per APD. The standard deviation in gain between the APDs in the array ranged from 1.8 to 6.5% as the gain was varied from 50 to 108. A fast, low-noise, multi-channel charge sensitive preamplifier application-specific integrated circuit (ASIC) was developed for the APD readout. The amplifier had a rise time of 8 ns, a noise floor of 515 e- rms and a 9 e- pF(-1) noise slope. An acquired flood image showed that all 100 crystals from the block detector could be resolved. Timing measurements with single-channel LSO-APD detectors, as well as with the array, against a plastic scintillator and PMT assembly showed a time resolution of 1.2 ns and 2.5 ns, respectively. The energy resolution measured with a single 4.0 x 4.0 x 10 mm3 LSO crystal, wrapped in four-layer polytetrafluoroethylene (PTFE) tape and coupled with optical grease on a single APD of the array, yielded 15% (full width at half maximum, FWHM) at 511 keV. Stability tests over 9 months of operation showed that the APD arrays do not degrade appreciably. These results demonstrate the ability to decode densely packed LSO scintillation blocks with compact APD arrays. The good timing and energy resolution makes these detectors suitable for high resolution PET.

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

“…The G-APD strip detector enables a high multiplexing, which reduces the number of readout channels compared with common PET block detectors. 14,40 The low number of readout channels reduces the cost and minimizes power consumption and cables, which is important for integrated PET/MR systems. The detector further combines high detection sensitivity with DoI information to maintain a good spatial resolution across the entire FOV.…”

“…1 PET/MRI also opens new avenues for clinical diagnosis [2][3][4][5][6][7] and basic research, specifically in the realms of oncology 8 and neurology. [9][10][11] Clinical and preclinical PET/MRI could not have been realized without the development of semiconductor based PET detectors [12][13][14] which enabled their integration into a MR bore and the simultaneous acquisition of PET and MR data while maintaining the full performance of both imaging modalities. [15][16][17] Avalanche photodiodes (APDs) were initially the only candidates for efficient scintillation light detection that could be operated in high magnetic fields.…”

“…However, APDs have a gain of 10 2 and a timing resolution in the nanosecond range, making their performance inferior compared with conventional photomultipliers tubes (PMTs). 14,15 The next generation of APDs are known as Geiger mode avalanche photodiodes (G-APDs) and are promising candidates for replacing both PMTs and APDs, especially in multimodality imaging devices where space is limited or magnetic fields are applied. [18][19][20][21] G-APDs reach a gain comparable to PMTs, of the order of 10 6 , and provide a timing performance in connection with a fast scintillator in the picosecond range.…”

A Novel Time-Based Readout Scheme for a Combined PET-CT Detector Using APDs

“…From [16]- [18], it turns out that our time-based approach of reading and processing coincident photon data from an APD circuit is comparable to classical methods where APD signals are digitized with ADCs. However, timing resolution of the order of 1 ns is relatively poor when electronic circuits with significantly In an approach similar to the one by Casey et al [19] we factorize the overall timing uncertainty into three parts corresponding to the three detector components in our system, each contributing to time jitter: (I) the scintillating crystal, (II) the APD photodetector, and (III) the electronic circuit.…”

Clinical applications of PET/MRI: current status and future perspectives

“…Conventional PET detectors consist of scintillation crystals and photomultipliers, and the latter, being very sensitive to magnetic fields, cannot be used in integrated PET/MRI systems. Hence, one approach was to replace photomultipliers by avalanche photodiodes (APDs), which are insensitive to even strong magnetic fields (4). The scintillation crystals used in PET/MRI scanners are usually composed of lutetium ortho-oxysilicate, with the advantage of only minor disturbances of magnetic field homogeneity (Fig.…”