High resolution detectors for whole-body PET scanners by using dual-ended readout

Abstract

Background Most current whole-body positron emission tomography (PET) scanners use detectors with high timing resolution to measure the time-of-flight of two 511 keV photons, improving the signal-to-noise ratio of PET images. However, almost all current whole-body PET scanners use detectors without depth-encoding capability; therefore, their spatial resolution can be affected by the parallax effect. Methods In this work, four depth-encoding detectors consisting of LYSO arrays with crystals of 2.98 × 2.98 × 20 mm3, 2.98 × 2.98 × 30 mm3, 1.95 × 1.95 × 20 mm3, and 1.95 × 1.95 × 30 mm3, respectively, were read at both ends, with 6 × 6 mm2 silicon photomultiplier (SiPM) pixels in a 4 × 4 array being used. The timing signals of the detectors were processed individually using an ultrafast NINO application-specific integrated circuit (ASIC) to obtain good timing resolution. The 16 energy signals of the SiPM array were read using a row and column summing circuit to obtain four position-encoding energy signals. Results The four PET detectors provided good flood histograms in which all crystals could be clearly resolved, the crystal energy resolutions measured being 10.2, 12.1, 11.4 and 11.7% full width at half maximum (FWHM), at an average crystal depth of interaction (DOI) resolution of 3.5, 3.9, 2.7, and 3.0 mm, respectively. The depth dependence of the timing of each SiPM was measured and corrected, the timing of the two SiPMs being used as the timing of the dual-ended readout detector. The four detectors provided coincidence time resolutions of 180, 214, 239, and 263 ps, respectively. Conclusions The timing resolution of the dual-ended readout PET detector was approximately 20% better than that of the single-ended readout detector using the same LYSO array, SiPM array, and readout electronics. The detectors developed in this work used long crystals with small cross-sections and provided good flood histograms, DOI, energy, and timing resolutions, suggesting that they could be used to develop whole-body PET scanners with high sensitivity, uniform high spatial resolution, and high timing resolution.

Depth‐of‐interaction positron emission tomography detector with 45° tilted silicon photomultipliers using dual‐ended signal readout

“…A PET detector based on dual-ended signal readout provides continuous DOI information with excellent timing, energy, and DOI resolutions. [24][25][26][27][28][29][30][31] Therefore, it has been widely utilized in various high-resolution PET systems, particularly for small-animal and peripheral human organ imaging. [40][41][42][43] However, the increased material cost of the dual-ended signal readout scheme is a critical drawback since it requires twice the number of photosensors and readout electronics.…”

“…The better energy and timing resolution of this detector than our detector owed to simple one-to-one coupling minimizing light collection loss and readout electronics noise. Liu et al 30 tested with similar crystal conditions to our condition for whole-body PET application without using sparse SiPM configurations. The DOI and energy resolution of this detector were 3.5 mm and 10.2% while the timing resolution of this detector was 180 ps with ultrafast NINO application-specific integrated circuit (ASIC), 44 which is better than our detector timing performance (411 ps).…”

“…A PET detector based on dual‐ended signal readout provides continuous DOI information with excellent timing, energy, and DOI resolutions 24–31 . Therefore, it has been widely utilized in various high‐resolution PET systems, particularly for small‐animal and peripheral human organ imaging 40–43 .…”

“…[21][22][23] Thanks to the accurate DOI estimation and simplicity in DOI calibration,the dual-ended readout method is one of the most intensively investigated approaches. [24][25][26][27][28][29][30][31] However, it requires twice as many photosensors and electronics compared to other DOI measurement methods 14,[32][33][34][35] based on a single-ended signal readout. Therefore, cost-effective PET detectors based on sparsely arranged photosensor configurations have been proposed to reduce detector manufacturing costs for the dual-ended readout method.…”

“…Thanks to the accurate DOI estimation and simplicity in DOI calibration, the dual‐ended readout method is one of the most intensively investigated approaches 24–31 . However, it requires twice as many photosensors and electronics compared to other DOI measurement methods 14,32–35 based on a single‐ended signal readout.…”