The authors’ laboratory is developing a dual-panel, breast-dedicated PETsystem. The detector panels are built from dual-LSO-position-sensitive avalanche photodiode (PSAPD) modules—units holding two arrays of LSO crystals, where each array is coupled to a PSAPD. When stacked to form an imaging volume, these modules are capable of recording the 3-D coordinates of individual interactions of a multiple-interaction photon event (MIPE). The small size of the scintillation crystal elements used increases the likelihood of photon scattering between crystal arrays. In this article, the authors investigate how MIPEs impact the systemphoton sensitivity, the data acquisition scheme, and the quality and quantitative accuracy of reconstructedPETimages.Methods:
A Monte Carlo simulated PET scan using the dual-panel system was performed on a uniformly radioactive phantom for the photon sensitivity study. To establish the impact of MIPEs on a proposed PSAPD multiplexing scheme, experimental data were collected from a dual-LSO-PSAPD module edge-irradiated with a point source, the data were compared against simulation data based on an identical setup. To assess the impact of MIPEs on the dual-panel PETimages, a simulated PET of a phantom comprising a matrix of hot spherical radiation sources of varying diameters immersed in a warm background was performed. The list-mode output data were used for image reconstruction, where various methods were used for estimating the location of the first photon interaction in MIPEs for more accurate line of response positioning. The contrast recovery coefficient (CRC), contrast to noise ratio (CNR), and the full width at half maximum spatial resolution of the spheres in the reconstructed images were used as figures of merit to facilitate comparison.Results:
Compared to image reconstruction employing only events with interactions confined to one LSO array, a potential single photon sensitivity gain of ( for coincidence) was noted for a uniform phantom when MIPEs with summed-energy falling within a ±12% window around the photopeak were also included. Both experimental and simulation data demonstrate that of the events whose summed-energy deposition falling within that energy window interacted with both crystal arrays within the same dual-LSO-PSAPD module. This result establishes the feasibility of a proposed multiplexed readout of analog output signals of the two PSAPDs within each module. Using MIPEs with summed-energy deposition within the photopeak window and a new method for estimating the location of the first photon interaction in MIPEs, the corresponding reconstructed image exhibited a peak CNR of 7.23 for the 8 mm diameter phantom spheres versus a CNR of 6.69 from images based solely on single LSO array interaction events. The improved systemphoton sensitivity could be exploited to reduce the scan time by up to approximately 10%, while still maintaining image quality comparable to that achieved if MIPEs were excluded.Conclusions:
MIPE distribution in the detectors allows the proposed photodetector multiplexing arrangement without significant information loss. Furthermore, acquiring MIPEs can enhance systemphoton sensitivity and improve PETimageCNR and CRC. The system under development can therefore competently acquire and analyze MIPEs and produce high-resolution PETimages.
The authors acknowledge the support of this work by the U.S. National Institute of Health under Grant Nos. R01 CA119056, R01 CA119056-S1 (ARRA), and R33 EB003283, and the support of Stanford Bio-X Graduate Fellowships for Dr. Guillem Pratx and Frances W. Y. Lau. The authors also wish to thank Dr. Arne Vandenbroucke for his time and valuable input towards the compilation of this manuscript.
II. BREAST-DEDICATED IMAGINGSYSTEM
II.A. Detector geometry
II.B. PSAPD readout configuration
III.A. Photon sensitivity
III.B. Effect of PSAPD multiplexed readout scheme on effective photon sensitivity
III.C. Reconstructed image quality and quantification
IV.A. Photon sensitivity
IV.B. Effect of PSAPD multiplexing on effective photon sensitivity
IV.C. Reconstructed image quality and quantification
V.A. Photon sensitivity
V.B. PSAPD multiplexing feasibility
V.C. Reconstructed image quality
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