Abstract
Bismuth germanate oxide (BGO) scintillators can be re-introduced in time-of-flight positron emission tomography (TOF-PET) by exploiting the Cherenkov luminescence emitted as a result from 511 keV interactions. Accessing the timing information from the relatively few emitted Cherenkov photons is now possible due to the recent improvements in enhanced near-ultraviolet high-density (NUV-HD) silicon photomultiplier (SiPM) technology, fast and low noise readout electronics, and the development of efficient data post-processing methods. In this work, we aim to develop a scalable detector element able to achieve excellent coincidence time resolution (CTR) required for TOF-PET using BGO scintillator elements of various lengths. The proposed detector element is optically coupled to 3.14 × 3.14 mm2 NUV-sensitive SiPMs mounted on a custom design circuit board. In particular, we have evaluated the CTR performance of BGO crystal elements of dimensions 3 × 3 × 3 mm3, 3 × 3 × 5 mm3, 3 × 3 × 10 mm3, and 3 × 3 × 15 mm3, with chemically etched surfaces and wrapped in Teflon tape. To achieve excellent CTR performance, we apply state-of-the-art post-processing methods during data analysis. Best values of 156 ± 6 ps, 188 ± 5 ps, 228 ± 8 ps, and 297 ± 8 ps CTR FWHM have been achieved for the 3, 5, 10, and 15 mm length BGO crystals, respectively. These values improve to 105 ± 6 ps, 127 ± 8 ps, 133 ± 4 ps, and 189 ± 8 ps CTR FWHM, when only considering the Cherenkov component of the timing signal, which is extracted by considering the events with the fastest rise time (20% of the total data). The accurate classification of the events based on their rise time is possible; thanks to the implementation of a dual threshold approach that sets the lower threshold below one light photon equivalent level and the upper one above the signal amplitude of a single photon avalanche diode (SPAD).
Highlights
BGo-Based time-of-flight positron emission tomography (TOF-PET) lutetium-based fast scintillators such as cerium-doped lutetium oxy-orthosilicate [Lu2SiO5(Ce) or LSO(Ce)] and lutetiumyttrium oxy-orthosilicate [Lu1.8Y0.2SiO5(Ce) or LYSO(Ce)]
An important milestone achieved to exploit Cherenkov light detection was the recent improvement of the photodetector technology such as silicon photomultipliers (SiPMs) with good photon detection efficiency (PDE) in the near-ultraviolet and low single photon time resolution (SPTR) values combined with fast, low noise readout electronics [12,13,14]
Note that due to the low-noise level of our high-speed custom-designed electronic readout combined with enhanced UV Broadcom SiPMs, the acquired timing signals are very clean and fast which may lead to good coincidence time resolution (CTR) and a better discrimination of the fast and slow luminescence components
Summary
BGo-Based TOF-PET lutetium-based fast scintillators such as cerium-doped lutetium oxy-orthosilicate [Lu2SiO5(Ce) or LSO(Ce)] and lutetiumyttrium oxy-orthosilicate [Lu1.8Y0.2SiO5(Ce) or LYSO(Ce)]. In [10], the authors used the Philips DPC3200 digital SiPMs [23], which allow them to provide an individual timestamp from the first detected light photon (above noise) yielding ~400 ps FWHM CTR for 20 mm length BGO crystals at room temperature and without applying any correction These studies, among other, have demonstrated the feasibility to develop TOF-capable PET detector modules that employ a mixture of Cherenkov and slow component luminescence photons by using existing photosensor technologies coupled to BGO crystals with lengths that provide adequate photon detection efficiency for clinical TOFPET [24]. We have developed a scalable readout electronics board that consists of an improved version of the lownoise, high-frequency, and high-gain circuit presented in [4], combined using 3.14 × 3.14 mm NUV-sensitive Broadcom®
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