SiPM-based System Research Articles

Evaluation of SiPM-based readout system with gain stabilization for TL dosimetry

As the silicon photomultiplier (SiPM) technology has developed and matured, it has opened up avenues for its use in various luminescence dosimetry applications. However, the temperature sensitivity of SiPMs needs to be considered in settings where a SiPM-driven system may be affected by heat, such as during thermoluminescence (TL) measurements. This study investigated the TL signal reproducibility and temperature dependence of SiPMs (3×3mm2,50μm) using a Risoe TL/OSL-DA-20 reader, a gain stabilizing driver circuit, and a data acquisition (DAQ) module. The signal variation was insignificant when the temperature varied by less than 2 °C. However, when there was no temperature control, the signal loss occurred due to increased dark counts. We assessed four commercial dosimeters and compared them to conventional TL detection via a photomultiplier tube (PMT) in terms of dose-response, detection limits, and TL glow-curve characteristics. The slope in the dose-response (i.e., sensitivity) of the SiPM-based system was 1.5 to 3 times lower compared to PMT depending on the dosimeter. We explored the viability of TL readings by examining the potential reduction in sensitivity and dark counts due to the SiPM's photon-resolving feature. While the evaluation results of the suggested system demonstrate its practical usefulness, there are still unexplored areas that warrant further investigation. These are discussed in relation to the dark count rate, which is a major parameter that can impede the overall performance.

A high-performance custom photodetection system to probe the light yield enhancement in oriented crystals

Scintillating homogeneous detectors represent the state of the art in electromagnetic calorimetry. Moreover, the currently neglected crystalline nature of the most common inorganic scintillators can be exploited to achieve an outstanding performance boost in terms of compactness and energy resolution. In fact, it was recently demonstrated by the AXIAL/ELIOT experiments that a strong reduction in the radiation length inside PWO, and a subsequent enhancement in the scintillation light emitted per unit thickness, are attained when the incident particle trajectory is aligned with a crystal axis within ~ 1°. A SiPM-based system has been developed to directly probe this remarkable effect by measuring the scintillation light emitted by a PWO sample. The same concept could be applied to full-scale detectors that would feature a design significantly more compact than currently achievable and unparalleled resolution in the range of interest for present and future experiments.

Silicon-photomultiplier-based PET/CT reduces the minimum detectable activity of iodine-124

The radioiodine isotope pair 124I/131I is used in a theranostic approach for patient-specific treatment of differentiated thyroid cancer. Lesion detectability is notably higher for 124I PET (positron emission tomography) than for 131I gamma camera imaging but can be limited for small and low uptake lesions. The recently introduced silicon-photomultiplier-based (SiPM-based) PET/CT (computed tomography) systems outperform previous-generation systems in detector sensitivity, coincidence time resolution, and spatial resolution. Hence, SiPM-based PET/CT shows an improved detectability, particularly for small lesions. In this study, we compare the size-dependant minimum detectable 124I activity (MDA) between the SiPM-based Biograph Vision and the previous-generation Biograph mCT PET/CT systems and we attempt to predict the response to 131I radioiodine therapy of lesions additionally identified on the SiPM-based system. A tumour phantom mimicking challenging conditions (derived from published patient data) was used; i.e., 6 small spheres (diameter of 3.7–9.7 mm), 9 low activity concentrations (0.25–25 kBq/mL), and a very low signal-to-background ratio (20:1). List-mode emission data (single-bed position) were divided into frames of 4, 8, 16, and 30 min. Images were reconstructed with ordinary Poisson ordered-subsets expectation maximization (OSEM), additional time-of-flight (OSEM-TOF) or TOF and point spread function modelling (OSEM-TOF+PSF). The signal-to-noise ratio and the MDA were determined. Absorbed dose estimations were performed to assess possible treatment response to high-activity 131I radioiodine therapy. The signal-to-noise ratio and the MDA were improved from the mCT to the Vision, from OSEM to OSEM-TOF and from OSEM-TOF to OSEM-TOF+PSF reconstructed images, and from shorter to longer emission times. The overall mean MDA ratio of the Vision to the mCT was 0.52 ± 0.18. The absorbed dose estimations indicate that lesions ≥ 6.5 mm with expected response to radioiodine therapy would be detectable on both systems at 4-min emission time. Additional smaller lesions of therapeutic relevance could be detected when using a SiPM-based PET system at clinically reasonable emission times. This study demonstrates that additional lesions with predicted response to 131I radioiodine therapy can be detected. Further clinical evaluation is warranted to evaluate if negative 124I PET scans on a SiPM-based system can be sufficient to preclude patients from blind radioiodine therapy.

From a PMT-based to a SiPM-based PET system: a study to define matched acquisition/reconstruction parameters and NEMA performance of the Biograph Vision 450

BackgroundThe purpose of this work was to propose an approach based on noise measurement to adapt present clinical acquisition and reconstruction parameters adapted to a PMT-based system (Biograph mCT) to a SiPM-based system (Biograph Vision 450) sharing identical geometrical properties. The NEMA performance (NEMA) of the recently released Biograph Vision 450 PET/CT (Vision) was also derived.MethodsAll measurements were conducted on Vision and Biograph mCT with TrueV (mCT). A full NEMA-based performance was derived for Vision only. The adaptation of acquisition and reconstruction parameters from mCT to Vision was done using the NEMA image quality phantom. The noise level reached using mCT was set as the reference value for six different numbers of net true coincidences. The noise level computed using Vision was matched to the reference noise level (within 0.01%) using a different reconstruction set-up to determine the potential reduction of count numbers for the same noise level.ResultsVision sensitivity was 9.1 kcps/MBq for a timing resolution of 213 ps at 5.3 kBq/mL. The NEMA-based CR for the 10-mm sphere was better than 75% regardless the reconstruction set-up studied. The mCT reference noise properties could be achieved using Vision with a scan time reduction (STR) of 1.34 with four iterations and a 440 × 440 matrix size (or STR = 1.89 with a 220 × 220 matrix size) together with a 3D CR improvement of 53% for the 10-mm sphere (24% using 220 × 220).ConclusionThe Vision exhibited improved NEMA performances compared to mCT. Using the proposed approach, the time acquisition could be divided by almost two, while keeping the same noise properties as that of mCT with a marked improvement of contrast recovery.

Assessment of the potential of SiPM-based systems for bioluminescence detection

Bioluminescence detection requires single-photon sensitivity, extremely low detection limits and wide dynamic range. Such performances were traditionally assured by photomultiplier-tubes based systems. However, development of novel applications and industrialization call for the introduction of more robust, compact and scalable devices. Silicon photomultipliers were recently put forward as the alternative to phototubes for a new generation of flexible and user friendly instruments. In this article, the figures of merit of a silicon-photomultiplier based system relying on a compact, low cost system are investigated. Possible implementations are proposed and a proof-of-principle bioluminescence measurement is performed.

Characterization of a mixed-sinusoid multiplexing scheme with silicon photomultipliers and an inorganic scintillator

Use of silicon photomultipliers (SiPMs) in radiation detection and imaging systems has been dramatically growing, and, because of their small size, the ability to effectively readout multiple SiPMs in a single channel is a critical objective to developing multichannel SiPM-based systems. Therefore, we have developed a relatively simple multiplexing method for SiPMs based on adding a specific sinusoid to the SiPM signal waveform prior to digitization, where the sinusoid serves as the tagging signal. This method has been previously successfully tested with organic scintillators, and this work characterizes its applicability to inorganic scintillators, specifically LYSO crystals with two different SiPMs. The energy and timing resolution is found to be largely unperturbed by this method for appropriate sinusoids, and excellent signal origin reconstruction is obtained. The ideal tagging sinusoids for adding have frequencies greater than 5 MHz and smaller peak-to-peak amplitudes of approximately 50 mV. The potential to use this method with detection systems comprised of both organic and inorganic scintillators is also demonstrated and discussed in detail.

Comparison between silicon photomultiplier-based and conventional PET/CT in patients with suspected lung cancer\u2014a pilot study

BackgroundLung cancer is one of the most common cancers in the world. Early detection and correct staging are fundamental for treatment and prognosis. Positron emission tomography with computed tomography (PET/CT) is recommended clinically. Silicon (Si) photomultiplier (PM)-based PET technology and new reconstruction algorithms are hoped to increase the detection of small lesions and enable earlier detection of pathologies including metastatic spread. The aim of this study was to compare the diagnostic performance of a SiPM-based PET/CT (including a new block-sequential regularization expectation maximization (BSREM) reconstruction algorithm) with a conventional PM-based PET/CT including a conventional ordered subset expectation maximization (OSEM) reconstruction algorithm. The focus was patients admitted for 18F-fluorodeoxyglucose (FDG) PET/CT for initial diagnosis and staging of suspected lung cancer. Patients were scanned on both a SiPM-based PET/CT (Discovery MI; GE Healthcare, Milwaukee, MI, USA) and a PM-based PET/CT (Discovery 690; GE Healthcare, Milwaukee, MI, USA). Standardized uptake values (SUV) and image interpretation were compared between the two systems. Image interpretations were further compared with histopathology when available.ResultsSeventeen patients referred for suspected lung cancer were included in our single injection, dual imaging study. No statically significant differences in SUVmax of suspected malignant primary tumours were found between the two PET/CT systems. SUVmax in suspected malignant intrathoracic lymph nodes was 10% higher on the SiPM-based system (p = 0.026). Good consistency (14/17 cases) between the PET/CT systems were found when comparing simplified TNM staging. The available histology results did not find any obvious differences between the systems.ConclusionIn a clinical setting, the new SiPM-based PET/CT system with a new BSREM reconstruction algorithm provided a higher SUVmax for suspected lymph node metastases compared to the PM-based system. However, no improvement in lung cancer detection was seen.

First results from the CMS SiPM-based hadronic endcap calorimeter

The CMS hadronic calorimeter employs a plastic-scintillator-based endcap detector. In early 2017, a 20° wedge of the endcap was upgraded with silicon photomultipliers (SiPMs) and readout electronics based on the QIE11 digitizer. Based on the excellent experience with this 20° pilot system in 2017, the entire endcap detector was upgraded with SiPMs in early 2018. We report on the first ever operation of SiPMs in a high-rate collider detector.We compare SiPM performance to that of the previous hybrid photodiode / QIE8-based readout and describe how the factor three improvement in photon-detection efficiency, increased longitudinal segmentation, and improved response stability allow for mitigation of scintillator radiation damage and simplified calibration. We report in situ measurements of radiation-induced SiPM dark current. Overall, we show that the upgraded SiPM-based system brings more than 50% improvement in radiation-induced response degradation.

Novel Method of Temperature Stabilization for SiPM-Based Detectors

One of the drawbacks of silicon-based photomultipliers is variation of performance with even small temperature fluctuations. The purpose of this work is to investigate a novel method of temperature stabilization of SiPM-based imaging device. Our prototype cooling system utilizes optically transparent cooling fluid as means of removing heat from the light detector and spreading scintillation light among several SiPM units. Cooled liquid passes through a 2 mm opening between two Mylar sheets. The Mylar sheets are held together with an aluminum frame. An array of SiPMs and an array of LYSO scintillation crystals are attached to opposite sides of the cooling light guide. Temperature uniformity of the optical surface was evaluated with an infrared camera. A temperature gradient of 0.09 °C/cm was measured along the direction of the coolant flow. The system was tested with a 5 × 5 array of Hamamatsu S10943 SiPMs coupled to a 16 × 16 matrix of 1.5×1.5×10 mm LYSO crystals. Testing procedures included evaluation of temperature dependence of detector gain, integrated noise, ability to resolve individual crystals and energy resolution. Detector gain varied by 9.3% over the range of 5 °C. Energy resolution change of 5% was observed over the same temperature range. Integrated noise contribution showed moderate increase of 2.2% over the range of 7 °C. The separation of individual crystals was found adequate with only a weak dependence of peak-to-valley contrast ratios on temperature. An assessment of performance stability at constant temperature revealed 0.2% variation in gain and 0.7% variation in energy resolution during an hour-long acquisition. It is concluded that the proposed method is a viable option for cooling and temperature stabilizing of SiPM-based systems.