Positron Emission Tomography Detector Research Articles

Performance of a high-resolution depth encoding PET detector using barium sulfate reflector

Small animal positron emission tomography (PET) is a well-established imaging modality in preclinical biomedical research. The performance of current small animal PET scanners is mainly limited by the detector performance and depth-encoding detectors are required to simultaneously achieve high spatial resolution and high sensitivity. In this work, the performance of a high-resolution dual-ended readout lutetium-yttrium oxyorthosilicate (LYSO) array using barium sulfate powder (BaSO4) as the inter-crystal reflector was measured for the first time and compared to that of a LYSO array using the most commonly used enhanced specular reflector (ESR). Both LYSO arrays have 18 × 18 crystals and the crystal size is about 0.62 × 0.62 × 20 mm3. The LYSO arrays are readout by two position-sensitive photomultiplier tubes (PSPMTs) from both ends. The flood histograms, energy resolution, depth of interaction (DOI) resolution and timing resolution were measured. The flood histograms of the LYSO array with BaSO4 reflector is much better than that of the LYSO array with ESR reflector. For the BaSO4 array, all crystals can be clearly resolved. For the ESR array, all crystals in one direction can be clearly resolved, but the edge 2–3 columns of the crystals in the other direction cannot be resolved. The average energy resolution of the BaSO4 and ESR arrays are 15.2% and 15.3%, respectively. The average DOI resolution of the BaSO4 array is 2.19 mm, which is 24% worse than the 1.76 mm DOI resolution of the ESR array. The timing resolution of both arrays is ~1.6 ns. The LYSO array with the new BaSO4 reflector provided an much better flood histogram in a high resolution dual-ended readout PET detectors as compared to the ESR array, and will be used to develop a small animal PET scanner that can simultaneously achieve uniform high spatial resolution, high sensitivity and low cost.

Radiation hardness of dsipm sensors in a proton therapy radiation environment

In vivo verification of dose delivery in proton therapy by means of positron emission tomography (PET) or prompt gamma imaging is mostly based on fast scintillation detectors. The digital silicon photomultiplier (dSiPM) allows excellent scintillation detector timing properties and is thus being considered for such verification methods. We present here the results of the first investigation of radiation damage to dSiPM sensors in a proton therapy radiation environment. Radiation hardness experiments were performed at the AGOR cyclotron facility at the KVI-Center for Advanced Radiation Technology, University of Groningen. A 150-MeV proton beam was fully stopped in a water target. In the first experiment, bare dSiPM sensors were placed at 25 cm from the Bragg peak, perpendicular to the beam direction, a geometry typical for an in situ implementation of a PET or prompt gamma imaging device. In the second experiment, dSiPM-based PET detectors containing lutetium yttrium orthosilicate scintillator crystal arrays were placed at 2 and 4 m from the Bragg peak, perpendicular to the beam direction; resembling an in-room PET implementation. Furthermore, the experimental setup was simulated with a Geant4-based Monte Carlo code in order to determine the angular and energy distributions of the neutrons and to determine the 1-MeV equivalent neutron fluences delivered to the dSiPM sensors. A noticeable increase in dark count rate (DCR) after an irradiation with about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> 1-MeV equivalent neutrons/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> agrees with observations by others for analog SiPMs, indicating that the radiation damage occurs in the single photon avalanche diodes and not in the electronics integrated on the sensor chip. It was found that in the in situ location, the DCR becomes too large for successful operation after the equivalent of a few weeks of use in a proton therapy treatment room (about 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> protons). For PET detectors in an in-room setup, detector performance was unchanged even after an irradiation equivalent to three years of use in a treatment room (3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> protons).

Low eddy current RF shielding enclosure designs for 3T MR applications.

Magnetic resonance-compatible medical devices operate within the MR environment while benefitting from the superior anatomic information of MRI. Avoiding electromagnetic interference between such instrumentation and the MR system is crucial. In this work, various shielding configurations for positron emission tomography (PET) detectors were studied and analyzed regarding radiofrequency (RF) shielding effectiveness and gradient-induced eddy current performances. However, the results of this work apply to shielding considerations for any MR-compatible devices. Six shielding enclosure configurations with various thicknesses, patterns, and materials were designed: solid and segmented copper, phosphor bronze mesh (PBM), and carbon fiber composite (CFC). A series of tests was performed on RF shielding effectiveness and the gradient-induced eddy current. For the shielding effectiveness, the solid copper with various thickness and PBM configurations yield significantly better shielding effectiveness (>15 dB) compared with CFC and segmented configurations. For the gradient-induced eddy current performance, the solid copper shielding configurations with different thicknesses showed significantly worse results, up to a factor of 3.89 dB, compared with the segmented copper, PBM, and the CFC configurations. We evaluated the RF shielding effectiveness and the gradient-induced eddy current artifacts of several shielding designs, and only the PBM showed positive outcomes for both aspects. Magn Reson Med 79:1745-1752, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Hybrid charge division multiplexing method for silicon photomultiplier based PET detectors

Silicon photomultiplier (SiPM) is widely utilized in various positron emission tomography (PET) detectors and systems. However, the individual recording of SiPM output signals is still challenging owing to the high granularity of the SiPM; thus, charge division multiplexing is commonly used in PET detectors. Resistive charge division method is well established for reducing the number of output channels in conventional multi-channel photosensors, but it degrades the timing performance of SiPM-based PET detectors by yielding a large resistor–capacitor (RC) constant. Capacitive charge division method, on the other hand, yields a small RC constant and provides a faster timing response than the resistive method, but it suffers from an output signal undershoot. Therefore, in this study, we propose a hybrid charge division method which can be implemented by cascading the parallel combination of a resistor and a capacitor throughout the multiplexing network. In order to compare the performance of the proposed method with the conventional methods, a 16-channel Hamamatsu SiPM (S11064-050P) was coupled with a 4 × 4 LGSO crystal block (3 × 3 × 20 mm3) and a 9 × 9 LYSO crystal block (1.2 × 1.2 × 10 mm3). In addition, we tested a time-over-threshold (TOT) readout using the digitized position signals to further demonstrate the feasibility of the time-based readout of multiplexed signals based on the proposed method. The results indicated that the proposed method exhibited good energy and timing performance, thus inheriting only the advantages of conventional resistive and capacitive methods. Moreover, the proposed method showed excellent pulse shape uniformity that does not depend on the position of the interacted crystal. Accordingly, we can conclude that the hybrid charge division method is useful for effectively reducing the number of output channels of the SiPM array.

Integrated optical and nuclear simulation of a monolithic LYSO:Ce based PET detector module

In the recent years new digital photon counter devices (also known as silicon photomultipliers, SiPMs) were designed and manufactured to be used specifically in positron emission tomography (PET) scanners. Finely pixelated SiPM arrays have opened new opportunities in PET detector development, such as the utilization of monolithic scintillator crystals. We worked out a simulation tool (SCOPE2) to assist the optimization and characterization of such PET detector modules. In the present paper we report the first application of SCOPE2 on the performance evaluation of a prototype PET detector module. The PET detector is based on monolithic LYSO:Ce scintillator crystal and a fully digital, silicon photon-counter, SPADnet-I. A new interface has been developed for SCOPE2 to access GATE simulation results. A combination of GATE and SCOPE2 was used to simulate excitation of the prototype PET detector with an electronically collimated γ -beam. Measurement results from the collimated γ-beam experiment were compared with the combined simulation. A good agreement was observed in the tendencies of total count spectrum and point of interaction distribution. We used the performance evaluation to understand and explain the measurement results in detail.

Design and Characterization of a Gradient-Transparent RF Copper Shield for PET Detector Modules in Hybrid MR-PET Imaging

This paper focuses on the design and the characterization of a frequency-selective shield for positron emission tomography (PET) detector modules of hybrid magnetic resonance-PET scanners, where the shielding of the PET cassettes is located close to the observed object. The proposed shielding configuration is designed and optimized to guarantee a high shielding effectiveness (SE) of up to 60 dB for ${B} _{1}$ -fields at the Larmor frequency of 64 MHz, thus preventing interactions between the radio-frequency (RF) coil and PET electronics. On the other hand, the shield is transparent to the gradient fields with the consequence that eddy-current artifacts in the acquired EPI images are significantly reduced with respect to the standard solid-shield configuration. The frequency-selective behavior of the shield is characterized and validated via simulation studies with CST MICROWAVE STUDIO in the megahertz and kilohertz range. Bench measurements with an RF coil built in-house demonstrated the high SE at the Larmor frequency. Moreover, measurements on a 4-T human scanner confirmed the abolishment of eddy current artifact and also provided an understanding of where the eddy currents occur with respect to the sequence parameters. Simulations and measurements for the proposed shielding concept were compared with a solid copper shielding configuration.

Development of a New PET Detector With Depth-Encoding Capability Using Wavelength-Shifting Fiber Readout

A new concept of positron emission tomography detector with depth-encoding capability is proposed and developed for small-animal imaging. The detector module is based on wavelength-shifting (WLS) fibers coupled to both sides of a scintillator array having a unique pattern. The scintillator array consists of $15 \times 15$ lutetium yttrium orthosilicate crystals with three different heights: 18, 20, and 22 mm. On the every other line, crystals having 2 mm shorter height are arranged to the ${x}$ -direction on the top and the ${y}$ -direction on the bottom of the array to make grooves for WLS fiber insertion. WLS fibers are inserted into these grooves and one end of each WLS fiber is coupled to a single channel silicon photomultiplier to detect scintillating lights trapped in the fiber. Field-programmable gate array combined 64-channel data acquisition (DAQ) system is used for DAQ and data processing, such as position, energy, and time decoding. The performance parameters, including pixel identification, energy resolution, depth of interaction (DOI) resolution, and timing resolution, were evaluated for proof of concept. The results proved that the design of detector allows not only to provide reasonable DOI information, but also to reduce the number of channels for sensors and electronics dramatically.

Characterization of 1.2×1.2 mm2 silicon photomultipliers with Ce:LYSO, Ce:GAGG, and Pr:LuAG scintillation crystals as detector modules for positron emission tomography

The design of a positron emission tomography (PET) scanner is specially challenging since it should not compromise high spatial resolution, high sensitivity, high count-rate capability, and good energy and time resolution. The geometrical design of the system alongside the characteristics of the individual PET detector modules contributes to the overall performance of the scanner. The detector performance is mainly influenced by the characteristics of the photo-detector and the scintillation crystal. Although silicon photomultipliers (SiPMs) have already proven to be promising photo-detectors for PET, their performance is highly influenced by micro-cell structure and production technology. Therefore, five types of SiPMs produced by KETEK with an active area size of 1.2 × 1.2 mm2 were characterized in this study. The SiPMs differed in the production technology and had micro-cell sizes of 25, 50, 75, and 100 μm. Performance of the SiPMs was evaluated in terms of their breakdown voltage, temperature sensitivity, dark count rate, and correlated noise probability. Subsequently, energy resolution and coincidence time resolution (CTR) of the SiPMs were measured with five types of crystals, including two Ce:LYSO, two Ce:GAGG, and one Pr:LuAG. Two crystals with a geometry of 1.5 × 1.5 × 6 mm3 were available from each type. The best CTR achieved was ∼ 240 ps, which was obtained with the Ce:LYSO crystals coupled to the 50 μm SiPM produced with the trench technology. The best energy resolution for the 511 keV photo-peak was ∼ 11% and was obtained with the same SiPM coupled to the Ce:GAGG crystals.

Highly multiplexed signal readout for a time-of-flight positron emission tomography detector based on silicon photomultipliers.

Maintaining excellent timing resolution in the generation of silicon photomultiplier (SiPM)-based time-of-flight positron emission tomography (TOF-PET) systems requires a large number of high-speed, high-bandwidth electronic channels and components. To minimize the cost and complexity of a system's back-end architecture and data acquisition, many analog signals are often multiplexed to fewer channels using techniques that encode timing, energy, and position information. With progress in the development SiPMs having lower dark noise, after pulsing, and cross talk along with higher photodetection efficiency, a coincidence timing resolution (CTR) well below 200ps FWHM is now easily achievable in single pixel, bench-top setups using 20-mm length, lutetium-based inorganic scintillators. However, multiplexing the output of many SiPMs to a single channel will significantly degrade CTR without appropriate signal processing. We test the performance of a PET detector readout concept that multiplexes 16 SiPMs to two channels. One channel provides timing information with fast comparators, and the second channel encodes both position and energy information in a time-over-threshold-based pulse sequence. This multiplexing readout concept was constructed with discrete components to process signals from a [Formula: see text] array of SensL MicroFC-30035 SiPMs coupled to [Formula: see text] Lu1.8Gd0.2SiO5 (LGSO):Ce (0.025mol. %) scintillators. This readout method yielded a calibrated, global energy resolution of 15.3% FWHM at 511keV with a CTR of [Formula: see text] FWHM between the 16-pixel multiplexed detector array and a [Formula: see text] LGSO-SiPM reference detector. In summary, results indicate this multiplexing scheme is a scalable readout technique that provides excellent coincidence timing performance.

Intercrystal Scatter Rejection for Pixelated PET Detectors

High-resolution positron emission tomography (PET) scanners often use pixelated scintillator arrays with lightsharing for the detection of gamma rays. The aim of this paper is to enhance the spatial resolution of such a pixelated scintillator detector by filtering out events with multiple interactions of gamma rays in the scintillator based on the measured light distributions. To develop and evaluate such enhancements in spatial resolution, we measure the point spread function (PSF) of our detector directly using a thinly collimated gamma ray beam setup, and then later verify their benefits on a full preclinical PET system with a hotrod phantom. The scintillator detector comprises a $30\times 30\times 12$ mm3 lutetium–yttrium oxyorthosilicate array with a pitch of 1 mm coupled to a digital silicon photomultiplier array via a 2-mm lightguide. We use a center of gravity algorithm for the crystal identification; however, the proposed filters are independent of the crystal identification algorithm. Investigating a single detector with our collimated gamma beam, we reject 15% of the events as multiple interaction while improving the crystal identification efficiency from 60.0% to 68.3% and the 90th-percentile diameter of the PSF from 7.88 to 3.98 mm. On system level, we analyze a line profile through two different rod sizes in a hotrod phantom. The filters reject 32% of the coincidences and increase the peak-to-valley ratio by 8% (0.9-mm rods) and by 18% (1.2-mm rods).

Color sensitive silicon photomultiplers with micro-cell level encoding for DOI PET detectors

There have been many studies on Depth Of Interaction (DOI) identification for high resolution Positron Emission Tomography (PET) systems, including those on phoswich detectors, double-sided readout, light sharing methods, and wavelength discrimination. The wavelength discrimination method utilizes the difference in wavelength of stacked scintillators and requires a color sensitive photodetector. Here, a new silicon photomultiplier (SiPM) coupled to a color filter (colorSiPM) was designed and fabricated for DOI detection. The fabricated colorSiPM has two anode readouts that are sensitive to blue and green color. The colorSiPM's response and DOI identification capability for stacked GAGG and LYSO crystals are characterized. The fabricated colorSiPM is sensitive enough to detect a peak of 662keV from a 137Cs source.

Focus on analytical equipment, sensors, and detectors

Focus on analytical equipment, sensors, and detectors

Development of a multiplexed readout with high position resolution for positron emission tomography

Detector signals for positron emission tomography (PET) are commonly multiplexed to reduce the number of digital processing channels so that the system can remain cost effective while also maintaining imaging performance. In this work, a multiplexed readout combining Anger position estimation algorithm and position decoder circuit (PDC) was developed to reduce the number of readout channels by a factor of 24, 96-to-4. The data acquisition module consisted of a TDC (50ps resolution), 4-channel ADCs (12bit, 105MHz sampling rate), 2GB SDRAM and USB3.0. The performance of the multiplexed readout was assessed with a high-resolution PET detector block composed of 2×3 detector modules, each consisting of an 8×8 array of 1.52×1.52×6mm3 LYSO, a 4×4 array of 3×3mm2 silicon photomultiplier (SiPM) and 13.4×13.4mm2 light guide with 0.7mm thickness. The acquired flood histogram showed that all 384 crystals could be resolved. The average energy resolution at 511keV was 13.7±1.6% full-width-at-half-maximum (FWHM) and the peak-to-valley ratios of the flood histogram on the horizontal and vertical lines were 18.8±0.8 and 22.8±1.3, respectively. The coincidence resolving time of a pair of detector blocks was 6.2ns FWHM. The reconstructed phantom image showed that rods down to a diameter of 1.6mm could be resolved. The results of this study indicate that the multiplexed readout would be useful in developing a PET with a spatial resolution less than the pixel size of the photosensor, such as a SiPM array.

Evaluation of a Sub-Millimeter Resolution PET Detector With a 1.2 mm Pitch TSV-MPPC Array One-to-One Coupled to LFS Scintillator Crystals and Inter-Crystal Scatter Studies With Individual Signal Readout

To develop a small animal positron emission tomography (PET) scanner for whole body imaging of mice, a sub-millimeter resolution PET detector has been constructed and its performance evaluated. This PET detector is composed of a 1.2 mm pitch multi-pixel photon counter (MPPC) $ {8\times 8}$ array with through-silicon via (TSV) structure one-to-one coupled to Lutetium Fine Silicate (LFS) scintillator crystals of size 1.13 mm $ {\times \,\,1.13}$ mm $ {\times \,\,10}$ mm each. To evaluate the intrinsic spatial resolution and the energy resolution in coincidence events, the coincidence response functions (CRFs) of the detector pair, located facing each other at a distance of 80 mm, were measured by scanning a 0.25 mm diameter 22Na point source in 0.1 mm steps. The data were acquired by the computer automated measurement and control (CAMAC) system. The average full width at half maximum (FWHM) of the CRFs was 0.75 mm without point source size corrections. The average FWHM of the energy resolution was 16% at 511 keV. The coincidence timing resolution (CTR) was also evaluated by facing the detector and a fast photomultiplier tube (PMT) coupled with a BaF2 crystal. The expected average FWHM of the CTR between the detectors was 770 ps. Additionally, to improve detector efficiency while suppressing the positioning errors, we propose an interaction-order scheme based on Compton kinematics and adapt it to the same data. We also perform Monte Carlo simulations using GEANT4 10.01 to evaluate the accuracy of the proposed positioning scheme and compare it to that of a centroid calculation scheme. As a result, we demonstrate that the accuracy of the proposed positioning scheme is better than that of a centroid calculation scheme when inter-crystal scatter events occur.

Evaluation of signal energy calculation methods for a light-sharing SiPM-based PET detector

Signals of a light-sharing positron emission tomography (PET) detector are commonly multiplexed to three analog pulses (E, X, and Y) and then digitally sampled. From this procedure, the signal energy that are critical to detector performance are obtained. In this paper, different signal energy calculation strategies for a self-developed SiPM-based PET detector, including pulse height and different integration methods, are evaluated in terms of energy resolution and spread of the crystal response in the flood histogram using a root-mean-squared (RMS) index. Results show that integrations outperform the pulse height. Integration using the maximum derivative value of the pulse E as the landmark point and 28 integrated points (448ns) has the best performance in these evaluated methods for our detector. Detector performance in terms of energy and position is improved with this integration method. The proposed methodology is expected to be applicable for other light-sharing PET detectors.

A depth-of-interaction PET detector using a stair-shaped reflector arrangement and a single-ended scintillation light readout

Positron emission tomography (PET) detectors with the ability to encode depth-of-interaction (DOI) information allow us to simultaneously improve the spatial resolution and sensitivity of PET scanners. In this study, we propose a DOI PET detector based on a stair-pattern reflector arrangement inserted between pixelated crystals and a single-ended scintillation light readout. The main advantage of the proposed method is its simplicity; DOI information is decoded from a flood map and the data can be simply acquired by using a single-ended readout system. Another potential advantage is that the two-step DOI detectors can provide the largest peak position distance in a flood map because two-dimensional peak positions can be evenly distributed. We conducted a Monte Carlo simulation and obtained flood maps. Then, we conducted experimental studies using two-step DOI arrays of 5 × 5 Lu1.9Y0.1SiO5:Ce crystals with a cross-section of 1.7 × 1.7 mm2 and different detector configurations: an unpolished single-layer (US) array, a polished single-layer (PS) array and a polished stacked two-layer (PT) array. For each detector configuration, both air gaps and room-temperature vulcanization (RTV) silicone gaps were tested. Detectors US and PT showed good peak separation in each scintillator with an average peak-to-valley ratio (PVR) and distance-to-width ratio (DWR) of 2.09 and 1.53, respectively. Detector PSRTV showed lower PVR and DWR (1.65 and 1.34, respectively). The configuration of detector PTAir is preferable for the construction of time-of-flight-DOI detectors because timing resolution was degraded by only about 40 ps compared with that of a non-DOI detector. The performance of detectors USAir and PSRTV was lower than that of a non-DOI detector, and thus these designs are favorable when the manufacturing cost is more important than timing performance. The results demonstrate that the proposed DOI-encoding method is a promising candidate for PET scanners that require high resolution and sensitivity and operate with conventional acquisition systems.

Modularized compact positron emission tomography detector for rapid system development.

We report the development of a modularized compact positron emission tomography (PET) detector that outputs serial streams of digital samples of PET event pulses via an Ethernet interface using the UDP/IP protocol to enable rapid configuration of a PET system by connecting multiple such detectors via a network switch to a computer. Presently, the detector is [Formula: see text] in extent (excluding I/O connectors) and contains an [Formula: see text] array of [Formula: see text] one-to-one coupled lutetium-yttrium oxyorthosilicate/silicon photomultiplier pixels. It employs cross-wire and stripline readouts to merge the outputs of the 216 detector pixels to 24 channels. Signals at these channels are sampled using a built-in 24-ch, 4-level field programmable gate arrays-only multivoltage threshold digitizer. In the computer, software programs are implemented to analyze the digital samples to extract event information and to perform energy qualification and coincidence filtering. We have developed two such detectors. We show that all their pixels can be accurately discriminated and measure a crystal-level energy resolution of 14.4% to 19.4% and a detector-level coincidence time resolution of 1.67ns FWHM. Preliminary imaging results suggests that a PET system based on the detectors can achieve an image resolution of [Formula: see text].

Performance evaluation of a sub-millimeter spatial resolution PET detector module using a digital silicon photomultiplier coupled LGSO array

In positron emission tomography (PET) for breast, brain and small animal imaging, the spatial resolution of a PET detector is crucial to obtain high quality PET images. In this study, a PET detector for sub-millimeter spatial resolution imaging purpose was assembled using 4×4 pixels of a digital silicon photomultiplier (dSiPM, DPC-3200-22-44, Philips) coupled with a 15×15 LGSO array with BaSO4 reflector, and a 1mm thick acrylic light guide for light distribution between the dSiPM pixels. The active area of each dSiPM pixel was 3.2×3.9mm2 and the size of each LGSO scintillator element was 0.7×0.7×6mm3. In this paper, we experimentally demonstrated the performance of the PET detector by measuring the energy resolution, 2D flood map, peak to valley (P/V) ratio, and coincidence resolving time (CRT). All measurements were performed at a temperature of 10±1℃. The average energy resolution was 15.6% (without correcting for saturation effects) at 511keV and the best CRT was 242±5ps. The 2D flood map obtained with an energy window of 400–600keV demonstrated clear identification of all pixels, and the average P/V ratio of the X- and Y-directions were 7.31 and 7.81, respectively. This study demonstrated that the PET detector could be suitable for application in high resolution PET while achieving good timing resolution.

Development of a novel depth-of-interaction encoding method and use of light spreading in a scintillation crystal array with single-ended readout

We designed a depth-of-interaction (DOI) positron emission tomography detector by applying a simple light-spreading method in a single-layer crystal array with a single-ended photosensor. By configuring different reflector patterns along the depth of the crystal, we were able to alter the light distribution of the gamma interaction at each depth. To evaluate the characteristics of the new DOI detector, we simulated the optical photon transport in the crystal array by using DETECT2000. Three different arrays comprising triangular-, square-, and hexagonal-shaped crystals were modeled. The 511-keV gamma-ray interactions were generated for all depths, and flood images were acquired. We confirmed that DOI layers could be distinguished in the obtained images and that the number of DOI layers depends on the number of sides of the polygonal crystals.

Reaching 200-ps timing resolution in a time-of-flight and depth-of-interaction positron emission tomography detector using phosphor-coated crystals and high-density silicon photomultipliers.

Current research in the field of positron emission tomography (PET) focuses on improving the sensitivity of the scanner with thicker detectors, extended axial field-of-view, and time-of-flight (TOF) capability. These create the need for depth-of-interaction (DOI) encoding to correct parallax errors. We have proposed a method to encode DOI using phosphor-coated crystals. Our initial work using photomultiplier tubes (PMTs) demonstrated the possibilities of the proposed method, however, a major limitation of PMTs for this application is poor quantum efficiency in yellow light, corresponding to the wavelengths of the converted light by the phosphor coating. In contrast, the red-green-blue-high-density (RGB-HD) silicon photomultipliers (SiPMs) have a high photon detection efficiency across the visible spectrum. Excellent coincidence resolving time (CRT; [Formula: see text]) was obtained by coupling RGB-HD SiPMs and [Formula: see text] lutetium fine silicate crystals coated on a third of one of their lateral sides. Events were classified in three DOI bins ([Formula: see text] width) with an average sensitivity of 83.1%. A CRT of [Formula: see text] combined with robust DOI encoding is a marked improvement in the phosphor-coated approach that we pioneered. For the first time, we read out these crystals with SiPMs and clearly demonstrated the potential of the RGB-HD SiPMs for this TOF-DOI PET detector.