Silicon Photomultiplier Pixels Research Articles

Decision Tree-Based Demultiplexing for Prism-PET

Signal multiplexing is necessary to reduce a large number of readout channels in positron emission tomography (PET) scanners to minimize cost and achieve lower power consumption. However, conventional weighted average energy methods cannot localize the multiplexed events and more sophisticated approaches are necessary for accurate demultiplexing. The purpose of this paper is to propose a non-parametric decision tree model for demultiplexing signals in prismatoid PET (Prism-PET) detector module that consisted of 16 × 16 lutetium yttrium oxyorthosilicate (LYSO) scintillation crystal array coupled to 8 × 8 silicon photomultiplier (SiPM) pixels with 64:16 multiplexed readout. A total of 64 regression trees were trained individually to demultiplex the encoded readouts for each SiPM pixel. The Center of Gravity (CoG) and Truncated Center of Gravity (TCoG) methods were utilized for crystal identification based on the demultiplexed pixels. The flood histograms, energy resolution, and depth-of-interaction (DOI) resolution were measured for comparison using with and without multiplexed readouts. In conclusion, our proposed decision tree model achieved accurate results for signal demultiplexing, and thus maintained the Prism-PET detector module’s high spatial and depth-of-interaction resolution performance while using our unique light-sharing-based multiplexed readout.

The silicon photomultiplier-based camera for the Cherenkov Telescope Array small-sized telescopes

The Cherenkov Telescope Array (CTA) is the next generation ground-based gamma-ray astronomy observatory, planned to comprise two arrays of imaging air Cherenkov telescopes (IACTs) located in the northern and southern hemispheres. Three telescope sizes are required to cover the CTA gamma-ray energy range from 20 GeV to 300 TeV. An array of several tens of Small-Sized Telescopes (SSTs) at the southern site situated in the Andes at Paranal in Chile, will provide unprecedented sensitivity above 1 TeV and up to 300 TeV, and offer the highest angular resolution of any instrument at these energies. Following a down selection from three prototype telescopes, the design finally selected for SST comprises a dual mirror Schwarzschild–Couder optic with a 4.3 m diameter primary mirror and a 1.8 m secondary mirror imaged by a silicon photomultiplier (SiPM)-based camera with a ∼9°field of view (FoV). The dual mirror optics produce a smaller plate-scale aplanatic focal plane allowing a small, low-cost camera to be employed, compared to that required for the conventional single mirror Davies-Cotton IACT design. The camera comprises an array of 2048 SiPM pixels, configured as 32 sensor and electronics modules each with an 8 × 8 pixel2 tile populated with 6 × 6 mm2 SiPM pixels. Full waveform capture on every channel is provided by the TARGET ASIC which performs the dual function of event triggering and waveform digitization of the full camera at 1 GSample/s. We describe the finalized SST camera design including its optimization for the production phase of the project anticipated to begin in 2023.

Interleaved signal multiplexing readout in depth encoding Prism-PET detectors.

Given the large number of readout pixels in clinical positron emission tomography (PET) scanners, signal multiplexing is an indispensable feature to reduce scanner complexity, power consumption, heat output, andcost. In this paper, we introduce interleaved multiplexing (iMux) scheme that utilizes the characteristic light-sharing pattern of depth-encoding Prism-PET detector modules with single-ended readout. In the iMux readout, four anodes from every other silicon photomultiplier (SiPM) pixels across rows and columns, which overlap with four distinct light guides, are connected to the same application-specific integrated circuit (ASIC) channel. The 4-to-1 coupled Prism-PET detector module was used which consisted of a 16× 16 array of 1.5 × 1.5 × 20 mm3 lutetium yttrium oxyorthosilicate (LYSO) scintillator crystals coupled to an 8 × 8 array with 3× 3mm2 SiPM pixels. A deep learning-based demultiplexing model was investigated to recover the encoded energy signals. Two different experiments were performed with non-multiplexed and multiplexed readouts to evaluate the spatial, depth of interaction (DOI), and timing resolutions of our proposed iMuxscheme. The measured flood histograms, using the decoded energy signals from our deep learning-based demultiplexing architecture, achieved perfect crystal identification of events with negligible decoding error. The average energy, DOI, and timing resolutions were 9.6 ± 1.5%, 2.9 ± 0.9mm, and 266 ± 19ps for non-multiplexed readout and 10.3 ± 1.6%, 2.8 ± 0.8mm, and 311 ± 28ps for multiplexed readout,respectively. Our proposed iMux scheme improves on the already cost-effective and high-resolution Prism-PET detector module and provides 16-to-1 crystal-to-readout multiplexing without appreciable performance degradation. Also, only four SiPM pixels are shorted together in the 8× 8 array to achieve 4-to-1 pixel-to-readout multiplexing, resulting in lower capacitance per multiplexedchannel.

Large-Area SiPM Pixels (LASiPs) in SPECT

A standard camera for Single Photon Emission Computed Tomography (SPECT) contains 50–100 photomultiplier tubes (PMTs). It is shielded by a thick layer of lead which makes it heavy and bulky. Its weight and size could be significantly reduced if replacing the PMTs by silicon photomultipliers (SiPMs). However, one would need a few thousands channels to fill a camera with SiPMs due to their small sensitive area. Alternatively, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We extended the simulation of a small camera employed with LASiPs that was presented in Guberman et al. (2021) to a large camera. The extension allowed us to study the feasibility of using larger LASiPs in a full-body SPECT camera. We found an intrinsic spatial resolution of ∼4 mm for a simulated pixel summing 25 SiPMs including SiPM noise at room temperature. Reducing the dark count rate (DCR) could improve the intrinsic spatial resolution to ∼3 mm.

Large-Area SiPM Pixels (LASiPs) in SPECT

A standard camera for Single Photon Emission Computed Tomography (SPECT) contains 50–100 photomultiplier tubes (PMTs) that occupy at least 50% of its volume. It is shielded by a thick layer of lead which makes it heavy and bulky. Replacing PMTs by silicon photomultipliers (SiPMs) could significantly reduce the weight and size of a SPECT camera. However, the main obstacle is the limited size of SiPMs: even with the largest commercially available SiPM of 6 × 6 mm2 a few thousand channels would be needed to fill a camera. As a solution, we propose to use Large Area SiPM Pixels (LASiPs) which are built by summing the currents of several SiPMs into a single output. We developed a LASiP prototype summing 8 SiPMs using the MUSIC ASIC. To test the feasibility of using this solution in SPECT, we built a proof-of-concept micro camera that consisted of four of our LASiP prototypes coupled to a 40 × 40 × 8 mm3 NaI(Tl) crystal. We were able to reconstruct simple images of a 99m Tc capillary with an intrinsic spatial resolution of ∼2 mm and an energy resolution of ∼11.6%. We also simulated the system with Geant4, finding a good agreement with our experimental results. The simulations were extended to a larger camera, aiming to study the impact of pixel size, shape and noise.

SiPM dynamic range for CEPC scintillator-based electromagnetic calorimeter

A high-granularity scintillator calorimeter readout with silicon photomultipliers (SiPMs) is an electromagnetic calorimeter (ECAL) candidate for experiments at the Circular Electron Positron Collider (CEPC). A critical design parameter of this ECAL candidate is the dynamic range of the SiPMs. This study investigates the SiPM dynamic range required for the CEPC scintillator ECAL. A model is developed on the basis of the operation principles of SiPMs to describe the response of an SiPM to light pulses within one recovery period by considering the cross-talk effect, photon detection efficiency, and number of pixels. The response curve of a 10000-pixel SiPM predicted by the model is consistent with the measured curve within 2% for an incident light pulse of up to 12000 photons. The intrinsic fluctuations of the SiPM response naturally exist in this model, and the correction of the saturation effect in the SiPM response is investigated. Monte Carlo (MC) simulation shows that the algorithm can restore the response linearity of an SiPM for an incident light pulse in which the number of photons is up to around six times the number of SiPM pixels. The model and correction program are implemented for full simulation of the ZH production Z → νν, H → γγ channel to evaluate the impact of the SiPM dynamic range of the CEPC scintillator ECAL on the reconstructed Higgs boson mass and the sensitivity to the Higgs signal in this channel. The results show that the CEPC scintillator ECAL equipped with no less than 4000 SiPM pixels and operated with a light yield of 20 photon-electrons per channel for a single minimum ionizing particle can meet the requirements for Higgs boson precision measurement in the di-photon channel at the CEPC.

Miniaturized USB-powered multi-channel module for gamma spectroscopy and imaging

LAILA is a miniaturized eight-channel electronic readout system for compact γ-ray detectors, combining high-resolution spectroscopy capability with position sensitivity. Compactness is achieved by the combination of a novel CMOS front-end ASIC (Application-Specific Integrated Circuit) for analog processing of a large signal current from Silicon PhotoMultiplier (SiPM) solid-state photodetectors, with a microcontroller-based data acquisition system. The adoption of automatic gain regulation in the gated-integrator stage of the ASIC offers an 84 dB dynamic range, combining single-photon sensitivity with an extended input photon energy range (20 keV-4MeV, using 30 μm-cell SiPMs). Using this module with properly merged 144 SiPM pixels coupled to a 3 in.-thick lanthanum bromide scintillation crystal, a 3% energy resolution at 662 keV and 1cm spatial resolution in the estimation of the interaction coordinates are experimentally demonstrated in this work.

Large-Area SiPM Pixels (LASiPs): A cost-effective solution towards compact large SPECT cameras.

Single Photon Emission Computed Tomography (SPECT) scanners based on photomultiplier tubes (PMTs) are still largely employed in the clinical environment. A standard camera for full-body SPECT employs ~50-100 PMTs of 4-8cm diameter and is shielded by a thick layer of lead, becoming a heavy and bulky system that can weight a few hundred kilograms. The volume, weight and cost of a camera can be significantly reduced if the PMTs are replaced by silicon photomultipliers (SiPMs). The main obstacle to use SiPMs in full-body SPECT is the limited size of their sensitive area. A few thousand channels would be needed to fill a camera if using the largest commercially-available SiPMs of 6×6mm2. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6×6mm2 SiPM. We built a proof-of-concept micro-camera consisting of a 40×40×8mm3 NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of 15×15mm2, where we were able to reconstruct images of a 99mTc capillary with an intrinsic spatial resolution of ~2mm and an energy resolution of ~11.6% at 140keV. We used these measurements to validate Geant4 simulations of the system. This can be extended to simulate a larger camera with more and larger pixels, which could be used to optimize the implementation of LASiPs in large SPECT cameras. We provide some guidelines towards this implementation.

Design and measurement of Trans-PET basic detector module II using 6× 6 SiPM array for small-animal PET

Silicon photomultiplier (SiPM) coupled scintillation detectors, are considered as promising tools for basic design of imaging instrumentation for the next generation PET, PET/MRI, SPECT and autoradiography scanners. The precise technical knowledge is inadequate, and still some challenges need to be addressed in order to successfully implement the SiPM technology in high resolution PET systems. Firstly, the advantages of SiPM pixel array 1:1 coupled crystal detector were obvious, and has minimized the position resolution errors of charge sharing in multiplexing circuits. However, in the system level, too many electronic channels have perplexed with complications, such as complex, messy electronics or dedicated ASIC chips. Multiplexing circuits were usually used to lower the complexity and cost of electronics, which has resulted in gradual deterioration of the performances of the detectors. Secondly, the light guide has become a necessity in high-resolution preclinical PET detectors. For a complete SiPM detector block, the light yield of outermost two rows/columns crystals were blurred due to the edge effects. In order to avoid this edge deterioration effect, crystal array size was reduced than that of the SiPM array in many PET detectors. The PET system built by these detectors had big gaps between the detector modules, which has largely affected the quality of reconstructed images. In order to solve these key problems, the Trans-PET basic detection module (BDM) II was designed and implemented in this study. This module was a flexible, easy to upgrade, simple, box geometry, small animal PET scanner. A better balance could be achieved by this detector, while reducing the electronic channels, and could simultaneously enhance the position resolution and time performance. A specially customized semi-cutting light guide had been designed, which could be optically multiplexed and diffused to optimize the effect of edge deterioration, so that both the outermost and inner crystals could be clearly distinguished. Specifically, in this PET module, two type crystal arrays with different crystal size had been designed, 13× 13 crystal array with 1.89 mm width and 18× 18 crystal array with 1.2 mm width, based on the same 6× 6 SiPM array and frond-end electronics. The total area of 6× 6 SiPM was 25.0× 25.0 mm2, which was similar to Hamamatsu PSPMT R8900. The area of the SiPM array was slightly smaller than the size of the crystal array, in order to reduce the gap of the PET system built by this detector. The purpose of this study was to evaluate the performance of this detector module, including position profile quality, energy resolution, timing resolution in different operating environment. Based on this detector module, PET scanners can easily be designed with different shapes such as, quadrilaterals, hexagonals, octagonals, dodecagonals, twenty-four-sides, and other shapes.

Development and test of a SiPM cluster for a SiPM version of the Cherenkov Telescope Array LST camera

The Large Size Telescopes (LSTs) are the largest telescopes of the Cherenkov Telescope Array (CTA). Their cameras are equipped with 1855 photomultiplier tube (PMT) pixels with GHz readout, to image the flashes of Cherenkov light emitted from atmospheric air-showers initiated by cosmic gamma rays. Silicon photomultipliers (SiPMs) are becoming valid alternatives for PMTs, and in fact many of the smaller telescopes in the array will feature a SiPM camera. To evaluate the performance of an LST SiPM-based camera we are building one of the LST camera elements (a cluster of 7 pixels with the readout electronics), replacing the PMTs with SiPM pixels. Most of the hardware of the baseline design is maintained, to keep the evaluation process simple and to use the existing calibration facilities. We discuss the design and construction of the demonstrator unit and some preliminary characterizations.

A Digital CMOS Silicon Photomultiplier Using Perimeter Gated Single Photon Avalanche Diodes With Asynchronous AER Readout

This paper presents a new architecture for a perimeter gated single photon avalanche diodes (PGSPADs) based CMOS digital silicon photomultiplier (SiPM) with fully digital asynchronous address event representation (AER) readout. A PGSPAD is a single photon avalanche diode with an additional polysilicon gate and mitigates the perimeter edge breakdown, modulates the noise floor, dynamic range, and sensitivity of the device. Spatial and temporal data compression techniques in the SiPM pixel improve dead time, and reduce electronics. Fill factor is improved using a compact, low power analog counter. The dead time improves by 25% with temporal compression improving by a factor of 10 for the pixel microcell. A $4\times 4$ pixel array in a standard $0.5~\mu \text{m}$ CMOS process is fully characterized for the dark counts as function of gate and excess bias as well as varying optical intensity. The array-level dynamic range is 142 dB.

High-Resolution Depth-Encoding PET Detector Module with Prismatoid Light-Guide Array.

Depth-encoding detectors with single-ended readout provide a practical, cost-effective approach for constructing high-resolution and high-sensitivity PET scanners. However, the current iteration of such detectors uses a uniform glass light-guide to achieve depth encoding, resulting in nonuniform performance throughout the detector array due to suboptimal intercrystal light sharing. We introduce Prism-PET, a single-ended-readout PET detector module with a segmented light-guide composed of an array of prismatoids that introduce enhanced, deterministic light sharing. Methods: High-resolution PET detector modules were fabricated with single-ended readout of polished multicrystal lutetium yttrium orthosilicate scintillator arrays directly coupled 4-to-1 and 9-to-1 to arrays of 3 × 3 mm silicon photomultiplier pixels. Each scintillator array was coupled at the nonreadout side to a light-guide (one 4-to-1 module with a uniform glass light-guide, one 4-to-1 Prism-PET module, and one 9-to-1 Prism-PET module) to introduce intercrystal light sharing, which closely mimics the behavior of dual-ended readout, with the additional benefit of improved crystal identification. Flood histogram data were acquired using a 3-MBq 22Na source to characterize crystal identification and energy resolution. Lead collimation was used to acquire data at specific depths to determine depth-of-interaction (DOI) resolution. Results: The flood histogram measurements showed excellent and uniform crystal separation throughout the Prism-PET modules, whereas the uniform glass light-guide module had performance degradation at the edges and corners. A DOI resolution of 5.0 mm full width at half maximum (FWHM) and an energy resolution of 13% FWHM were obtained in the uniform glass light-guide module. By comparison, the 4-to-1 coupled Prism-PET module achieved a DOI resolution of 2.5 mm FWHM and an energy resolution of 9% FWHM. Conclusion: PET scanners based on our Prism-PET modules with segmented prismatoid light-guide arrays can achieve high and uniform spatial resolution (9-to-1 coupling with ∼1-mm crystals), high sensitivity (20-mm-thick detectors and intercrystal Compton scatter recovery), good energy and timing resolutions (using polished crystals and after applying DOI correction), and compact size (depth encoding eliminates parallax error and permits smaller ring-diameter).

Optical simulation study on the spatial resolution of a thick monolithic PET detector

The intrinsic spatial resolution of clinical positron emission tomography (PET) detectors is ~3–4 mm. A further improvement of the resolution using pixelated detectors will not only result in a prohibitive cost, but is also inevitably accompanied by a strong degradation of important performance parameters like timing, energy resolution and sensitivity. Therefore, it is likely that future generation high resolution PET detectors will be based on continuous monolithic scintillation detectors. Monolithic detectors have attractive properties to reach superior 3D spatial resolution while outperforming pixelated detectors in timing, energy resolution and sensitivity.In this work, optical simulations including an advanced surface reflection model, allow us to investigate the influence of three parameters on the spatial resolution: silicon photomultiplier (SiPM) pixel size, photon detection efficiency (PDE) and the number of channels used to read out the SiPM array. A lutetium-yttrium oxyorthosilicate (LYSO) crystal with dimensions 50 × 50 × 16 mm3 coupled to an SiPM array is calibrated and a nearest neighbor (NN) algorithm is used to position events. Findings show that the tested parameters affect the spatial resolution resulting in 0.40–0.66 mm full width at half maximum (FWHM). Best resolution could be obtained with smaller SiPM pixels, higher PDE, and an individual channel readout. However, it was shown that combining channels by adding their signals can significantly reduce the amount of readout channels while having small or no significant impact on the resolution. The mean depth of interaction (DOI) estimation error is 1.6 mm. This study demonstrates the ultimate spatial resolution that can be obtained with this detector without being constrained by practical limitations of experimental setups. In the future these optical simulations may be used as a more precise and fast method to obtain calibration data for real monolithic detectors.

Performance of the Compact High Energy Camera SiPM Prototype Front-End Electronics proposed for the Cherenkov Telescope Array

The Compact High Energy Camera (CHEC) is a full-waveform capture camera, designed and proposed for the dual mirror, Schwarzschild–Couder, Small Sized Telescope of the Cherenkov Telescope Array. CHEC-S, the second prototype, is based upon silicon photomultiplier (SiPM) photodetectors optimised for single photon counting and nanosecond timing. The camera liquid-cooled focal plane plate comprises a total of 2048 SiPM pixels organised as 32 independent sensor and front-end electronics (FEE) modules providing event detection and signal digitisation of Cherenkov light flashes. Each module comprises an 8 × 8 tile of SiPM pixels, coupled to a 64-channel preamplifier-buffer followed by a FEE module based around the TARGET chipset, which combines triggering (T5TEA) and waveform capture (TARGET C) functionality.We describe a selection of end-to-end performance tests and results conducted at the University of Leicester in the UK. Testing was performed at single module level focusing on characterising the SiPM photodetectors, optimised preamplifier-buffer and updated CHEC-S FEE readout module. Presented results include single photoelectron response, gain-matching, signal range, electronic channel crosstalk, SiPM angular dependency and optical crosstalk.

Development of position sensitive detector module using scintillator and Si photomultiplier for hard x-ray imaging and spectroscopy

We explore the use of scintillation detectors coupled with silicon photomultipliers (SiPMs) as position sensitive hard x-ray spectroscopic detectors for potential applications in the field of high-energy astrophysics. X-ray photons on interaction with scintillation crystals generate optical photons and the distribution of these scintillation light photons is captured with the array of SiPM pixels, providing the spectral and spatial information of the incident x-ray photons. As the position is estimated by fitting the distribution of optical photons, it should be possible to achieve spatial resolution lesser than the pixel size. Development of two detector modules with CsI (Tl) and CeBr3 scintillators coupled with different sets of array of SiPM pixels is presented here. Spectral and spatial resolutions of both detector modules are characterized with experiments using x-ray lines from laboratory radioactive sources. It is shown that a faster scintillator with an array of low-noise SiPM pixels provides better spectral and spatial resolution and it is possible to achieve subpixel spatial resolution with such a detector module.

Design of a SiPM-based cluster for the Large-Sized Telescope camera of the Cherenkov Telescope Array

A Silicon Photomultiplier (SiPM)-based photodetector is being built to demonstrate its feasibility for an alternative silicon-based camera design for the Large Size Telescope (LST) of the Cherenkov Telescope Array. It has been designed to match the size of the standard Photomultiplier Tube (PMT) cluster unit and to be compatible with mechanics, electronics and focal plane optics of the first LST camera. Here, we describe the overall SiPM cluster design along with the main differences with respect to the currently used PMT cluster unit. The fast electronics of the SiPM pixel and its layout are also presented. In order to derive the best working condition for the final unit, we measured the SiPM performances in terms of gain, photo-detection efficiency and cross-talk. One pixel, a unit of 14 SiPMs, has been built. We will discuss also some preliminary results regarding this device and we will highlight the future steps of this project.

A SiPM-Readout ASIC for SPECT Applications

In this paper, we present ANGUS, an application specific integrated circuit (ASIC) for silicon photomultiplier (SiPM) readout designed for low-energy gamma imaging (140 keV), specifically targeting clinical single photon emission computed tomography (SPECT) applications based on Anger-type detectors. The chip is composed of 36 channels, each featuring a current conveyor input followed by an RC filter with a time constant programmable from 200 ns up to 10 $\mu \text{s}$ , a baseline holder and a peak stretcher stage. Multichannel readout is performed with a polling strategy thanks to two analog multiplexers. The chip has been designed to cope with input capacitance values of several nanofarad, like the ones featured by the large-sized SiPM pixels (8 mm ${\times }$ 8 mm) of the application. Despite being conceived for operation with slow scintillator crystals like cesium-iodide (CsI), this ASIC can successfully manage the readout of faster crystals like lutetium-yttrium oxyorthosilicate. Measurements of the ASIC carried out on a fully equipped SPECT detection module have shown an energy resolution of 13.7% at the 140-keV line of 99mTc, for a 5 cm ${\times }$ 5 cm gamma camera consisting of a continuous CsI crystal and a SiPM detection plane cooled at 0 °C.

Development and characterization of a 4 × 4mm2 pixel neutron scintillation detector using digital SiPMs

This work describes the development of the first demonstrator device for neutron detection based on a 6Li-glass as a scintillator and silicon photomultipliers (SiPM) as photodetector. For the first characterization, the scintillator was pixelated with a one to one correspondence between scintillator and SiPM pixels, and optical cross-talk between pixels was minimized. Measurements in a high luminosity neutron beam show the functionality of the device and allow for partial characterization. The position resolution is 4 × 4mm2 and the detection efficiency of neutrons is 91(6)% relative to the active area. The device is linear up to at least 600 kcps.

Validation of a highly integrated SiPM readout system with a TOF-PET demonstrator

We have developed a highly integrated, fast and compact readout electronics for Silicon Photomultiplier (SiPM) based Time of Flight Positron Emission Tomography (TOF-PET) scanners. The readout is based on the use of TOP-PET Application Specific Integrated Circuit (PETsys TOFPET1 ASIC) with 64 channels, each with its amplifier, discriminator, Time to Digital Converter (TDC) and amplitude determination using Time Over Threshold (TOT). The ASIC has 25 ps r.m.s. intrinsic time resolution and fully digital output. The system is optimised for high rates, good timing, low power consumption and low cost. For validating the readout electronics, we have built a technical PET scanner, hereafter called ``demonstrator'', with 2'048 SiPM channels. The PET demonstrator has 16 compact Detector Modules (DM). Each DM has two ASICs reading 128 SiPM pixels in one-to-one coupling to 128 Lutetium Yttrium Orthosilicate (LYSO) crystals measuring 3.1 × 3.1 × 15 mm3 each. The data acquisition system for the demonstrator has two Front End Boards type D (FEB/D), each collecting the data of 1'024 channels (8 DMs), and transmitting assembled data frames through a serial link (4.8 Gbps), to a single Data Acquisition (DAQ) board plugged into the Peripheral Component Interconnect Express (PCIe) bus of the data acquisition PC. Results obtained with this PET demonstrator are presented.

A Hand-Held, Intra-Operative Positron Imaging Probe for Surgical Applications

We have developed a prototype intra-operative $\beta^{+} $ imaging probe to help tumor removal and malignant tissue resection. The probe can be used during surgery to provide clear delineation of malignant tissues. Our probe consists of a hybrid scintillator coupled to a silicon photomultiplier (SiPM) array with associated front-end electronics encapsulated in an ergonomic aluminum housing. Pulse shape discrimination electronics has been implemented and integrated into the downstream data acquisition system. The field of view of the probe is $10 \times 10~\hbox{mm}^{2}$ realized by a 0.4 mm thick CsI:Tl scintillator coupled to a 1 mm thick LYSO. While CsI:Tl layer acts as $\beta^{+} $ sensitive detector, LYSO detects gamma radiation where the gamma response can be subtracted from the total signal to improve SNR and contrast. The thickness of the LYSO scintillator is optimized such that it acts as light diffuser to spread the scintillation light generated in CsI:Tl over multiple SiPM pixels for accurate estimation of the $\beta^{+} $ interaction location. The probe shows $ FWHM spatial resolution in the presence of large background radiation. The probe was used to study rabbits with tongue tumors. The experimental results show that the probe can successfully locate the tongue tumors in its active imaging area.