Lutetium Fine Silicate Research Articles

Study of low-energy gamma-ray detection performance of silicon photomultiplier with LaBr3(Ce) scintillator

Recent progress in the field of scintillators and silicon photomultipliers (SiPM) has allowed development of new scintillation detectors capable of detecting low-energy X- and gamma-ray sources that are widely used in medicine, security and industry. Such scintillation detectors are compact, insensitive to magnetic fields, have low operation voltages and are functional at room temperature. These advantages of SiPM are considered to solve the main problems facing scintillation detectors in medicine and industry today. Development of detectors of low-energy electromagnetic radiation is relevant now. Scintillation detectors based on lutetium fine silicate, LaBr3(Ce), NaI and silicon avalanche photomultipliers offer a great potential for use for X- and gamma-ray detection. The present work demonstrates the gamma-ray detection performance of a new micropixel avalanche photodiode (MAPD) array (16 (4×4) elements – 15×15 cm) with a LaBr3(Ce) scintillator (15×15×30 mm) using 177Lu and 133Ba isotopes as the gamma-ray sources.

Study of Čerenkov Light Emission in the Semiconductors TlBr and TlCl for TOF-PET.

Thallium bromide (TlBr) and thallium chloride (TlCl) are semiconductor materials with high transparency to visible light, high index of refraction, and high detection efficiency for gamma rays and annihilation photons. This manuscript reports on measurements of the light intensity and timing response of Čerenkov light emitted in one 3 mm × 3 mm × 5 mm slab of each of these materials operated in coincidence with a lutetium fine silicate (LFS) crystal with dimensions of 3 mm × 3 mm × 20 mm. A 22Na radioactive source was used. The measured average number of detected photons per event was 1.5 photons for TlBr and 2.8 photons for TlCl when these materials were coupled to a silicon photomultiplier. Simulation predicts these results with an overestimation of 12%. The best coincidence time resolution (CTR) for events in TlBr and TlCl were 329 ± 9 ps and 316 ± 9 ps, respectively, when events with 4 photons and >7 photons were selected. Simulation showed the CTR degraded from 120 ps to 405 ps in TlCl, and from 160 ps to 700 ps in TlBr when the first or second Čerenkov photon were selected. Results of this work show TlCl has a stronger Čerenkov light emission compared to TlBr and a greater potential to obtain the best timing measurements. Results also stress the importance of improving detection efficiency and transport of light to capture the first Čerenkov photon in timing measurements.

Evaluation of a Hamamatsu TOF-PET Detector Module With 3.2-mm Pitch LFS Scintillators and a 256-Channel SiPM Array

Using time-of-flight (TOF) information in image reconstruction improves image signal-to-noise ratio and quantitative accuracy in positron emission tomography (PET). A new TOF-PET detector module with a 3.2-mm pitch lutetium fine silicate (LFS) scintillator array one-to-one coupled to a 16×16 (256-ch) silicon photomultiplier (SiPM) array was made commercially available (C13500 series, Hamamatsu Photonics K. K.). In this study, as a candidate detector module for the next-generation brain-dedicated PET, we changed the scintillator length of 20 to 10 mm according to our helmet-type PET geometry and investigated the basic performance of the PET detector module, including its energy resolution, sensitivity, coincidence response function (CRF), and coincidence timing resolution (CTR). All performance values were compared with those of the 4.2-mm pitch 144-ch detector module which was selected for our current helmet-type PET prototype. The energy resolution was 12% at 511 keV. The sensitivity was about 10% lower compared with those of the 4.2-mm pitch module. The average full width at half maximum (FWHM) of the CRFs was 1.9 mm. The CTRs had values of 235-241 ps with various energy windows after applying timing calibration. The CTR was not significantly changed (<; 10 ps) at the single count rate of 412 kcps or lower.

245 ps-TOF brain-dedicated PET prototype with a hemispherical detector arrangement

Brain PET, which has led research in molecular imaging and diagnosis of brain cancer, epilepsy and neurodegenerative disorders, is being spotlighted again to promote earlier diagnosis of dementia with the advent of amyloid and tau tracers. To meet this demand, in this paper, we developed a brain-dedicated PET imaging device with a hemispherical detector arrangement, which provides comparable sensitivity with fewer detectors than conventional cylindrical geometries. The introduction of the time-of-flight (TOF) measurement capability was a key point for the development to get a gain in the image signal-to-noise ratio. Currently, whole-body PET scanners with around 200–400 ps coincidence resolving time (CRT) are commercially available. In order to obtain the same TOF gain which can be obtained with 400 ps CRT for a 30 cm diameter object, 267 ps CRT will be required for a 20 cm diameter object such as the human head. In this work, therefore, we aimed at developing a TOF brain-dedicated PET prototype with the hemisphere detector arrangement and the CRT faster than 267 ps. The detector was composed of a 12 × 12 lutetium fine silicate (LFS) array coupled with a 12 × 12 multi-pixel photon counter (MPPC) array. Each LFS crystal with a size of 4.14 × 4.14 × 10 mm3 was individually coupled to a separate MPPC. Singles list-mode data from each detector were stored, and coincidences were identified using a coincidence-detection software algorithm. The CRT of 245 ps was finally achieved as the system average after a fine timing correction. For image reconstruction, we implemented the list-mode TOF-OSEM. For a small rod phantom, rods of 3 mm diameter were clearly separated. Also, images of the 3D Hoffman brain phantom, which demonstrated clear contrast between gray and white matter, supported the effect of TOF information.

Neutron-Induced Radiation Damage in LYSO, BaF2, and PWO Crystals

One crucial issue for the application of scintillation crystals in future high-energy physics experiments is radiation damage in a severe radiation environment, such as the high luminosity large hadron collider. While radiation damage induced by ionization dose in inorganic scintillators is well understood, investigations are ongoing to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron-induced radiation damage in fast inorganic scintillators, lutetium yttrium oxyorthosilicate (LYSO)/lutetium fine silicate (LFS), BaF2, and PWO crystals were irradiated at Los Alamos Neutron Science Center by a combination of particles, including neutrons, protons, and $\gamma $ -rays. The results indicate that LYSO/LFS and BaF2 crystal plates are radiation hard up to a 1-MeV equivalent neutrons fluence of $9 \times 10^{15}$ equivalent neutron (neq)/cm2, but not PWO, and the neutron-induced radiation damage in LYSO crystals is a factor of ten less than protons.

Design study of a brain-dedicated time-of-flight PET system with a hemispherical detector arrangement

Time-of-flight (TOF) is now a standard technology for positron emission tomography (PET), but its effective use for small diameter PET systems has not been studied well. In this paper, we simulated a brain-dedicated TOF-PET system with a hemispherical detector arrangement. We modeled a Hamamatsu TOF-PET module (C13500-4075LC-12) with 280 ps coincidence resolving time (CRT), in which a 12 × 12 array of multi pixel photon counters (MPPCs) is connected to a lutetium fine silicate (LFS) crystal array of 4.1 × 4.1 mm2 cross section each, based on one-to-one coupling. On the other hand, spatial resolution degradation due to the parallax error should be carefully addressed for the small diameter PET systems. The ideal PET detector would have both depth-of-interaction (DOI) and TOF capabilities, but typical DOI detectors that are based on light sharing tend to degrade TOF performance. Therefore, in this work, we investigated non-DOI detectors with an appropriate crystal length, which was a compromise between suppressed parallax error and decreased sensitivity. Using GEANT4, we compared two TOF detectors, a 20 mm long non-DOI and a 10 mm long non-DOI, with a non-TOF, 4-layer DOI detector with a total length of 20 mm (i.e. 5 × 4 mm). We simulated a contrast phantom and evaluated the relationship between the contrast recovery coefficient (CRC) and the noise level (the coefficient of variation, COV) for reconstructed images. The 10 mm long non-DOI, which reduces the parallax error at the cost of sensitivity loss, showed better imaging quality than the 20 mm long non-DOI. For example, the CRC value of a 10 mm hot sphere at COV = 20% was 72% for the 10 mm long non-DOI, which was 1.2 times higher than that of the 20 mm long non-DOI. The converged CRC values for the 10 mm long non-DOI were almost equivalent to those of the non-TOF 4-layer DOI, and the 10 mm long non-DOI converged faster than the non-TOF 4-layer DOI did. Based on the simulation results, we evaluated a one-pair prototype system of the TOF-PET detectors with 10 mm crystal length, which yielded the CRT of 250 ± 8 ps. In summary, we demonstrated support for feasibility of the brain-dedicated TOF-PET system with the hemispherical detector arrangement.

Improving timing performance of double-ended readout in TOF-PET detectors

Scintillation crystals of 20 mm length or longer are needed for clinical time-of-flight positron emission tomography (TOF-PET) to ensure effective detection efficiency for gamma photons. However, the use of long crystals would deteriorate the key performance of TOF-PET detectors, time and spatial resolution, because of the variations in the travel times of the photons in crystals and the effects of parallax errors. In this work, we studied double-ended readout TOF-PET detectors based on coupling a long scintillation crystal to SiPMs at both ends for correcting the depth-dependent effects to improve the coincidence time resolution (CTR). In particular, we focused our attention to analyze timing performance using different correction methods, including trigger times of the individual photodetectors at both ends of the crystal, the simple average of the trigger times, and the weighted average based on the inverse variances of the depth-dependent corrected trigger times. For a 3 mm × 3 mm × 25 mm unpolished lutetium fine silicate (LFS) crystal with double-ended readout and practical head-on irradiation, a CTR of 246 ps FWHM can be achieved using depth-dependent timing-correction and weighted average time method compared to 280 ps FWHM using the conventional simple average time method and 393 ps FWHM using the conventional single-ended readout. The results show that the depth-dependent timing-correction and weighted average time method in double-ended readout can effectively correct for the trigger time variations in TOF-PET detector utilizing long unpolished crystals, resulting in an improvement in the CTR of as much as 37% compared to single-ended readout.

Development of a dual-end detector with TOF and DOI capabilities using crystal bars segmented by subsurface laser engraving

The quality and uniformity of positron emission tomography (PET) images can be improved significantly using a PET scanner, which has both time-of-flight (TOF) and depth-of-interaction (DOI) capabilities. We have already developed a DOI dual-end detector using segmented crystal bars by applying a subsurface laser engraving (SSLE) technique, and the DOI was determined by the ratio of the detected light between two readouts using the Anger calculation. In this study, we investigated the influence of the number of DOI segments on the performance of DOI identification and the coincidence timing performance of the detector. The detector consisted of a single lutetium fine silicate (LFS) crystal bar (3 × 3 × 20 mm 3 ) with various numbers of DOI segments that were made by applying the SSLE technique and Hamamatsu silicon photomultiplier (SiPM) modules. The maximum number of DOI segments was six, and the SiPM module included one hundred forty-four 4 mm × 4 mm SiPM readouts. The coincidence resolving time (CRT) of each DOI segment was obtained from the side irradiation of the dual-end detector. All DOI segments of the detector with 2, 3, 4, 5 or 6 DOI segments were clearly identified, and average energy resolutions of 9.8 ± 0.5% and 12.5 ± 1.4% were obtained at the 511 keV photo peak for the detectors with 2 DOI and 6 DOI segments, respectively. The minimum and maximum estimated CRT of 180 ± 6 ps and 236 ± 6 ps were obtained for the detectors with 2 DOI and 6 DOI segments, respectively. Insignificant differences were observed between the CRT values of different segments of one detector. Greater CRT values were obtained for detectors with larger DOIs. The results of this study prove that there is a high potential for segmented crystal bars using the SSLE technique as a good candidate for PET scanners with TOF and DOI capabilities, which can significantly improve the quality of PET images.

Prototype time-of-flight PET utilizing capacitive multiplexing readout method

Positron emission tomography (PET) is an imaging technique that provides the spatial distribution of radiopharmaceuticals labeled with positron emitting radioisotopes by detecting the gamma rays produced from positron–electron annihilation. Recently, a time-of-flight (TOF) PET has drawn an increasing attention because it is capable of reducing the scan time or injected dose with improved the signal-to-noise ratio (SNR) in reconstructed PET images by precisely localizing the emission point along the line-of-response using TOF information.This study presents a multiplexing method that can effectively reduce the number of readout channels of a silicon photomultiplier (SiPM) based TOF PET while achieving excellent timing resolution. A capacitive multiplexing method was employed that could improve the degradation of the timing performance occurring in a conventional resistive multiplexing method. In addition, a high-speed signal processing method is also presented for the TOF PET. A TOF PET prototype was developed to demonstrate the imaging capability of the TOF PET system.A flood histogram of a PET detector module, composed of an 8×8 array of 3.01×3.01×20.00 mm3 lutetium fine silicate (LFS) scintillators and an 8×8 array of 3.16×3.16 mm2 SiPMs, was acquired using the proposed method. All 64 scintillators were successfully resolved in the flood histogram. The average energy resolution and coincidence resolving time (CRT) were 14.2 ± 1.1% and 431 ± 41 ps full width at half maximum (FWHM), respectively. A tomographic image of the hot-rod phantom was successfully acquired using the TOF PET prototype, and rods with a size of 2.4 mm in diameter were clearly resolved in the reconstructed image.

Evaluation of LFS continuous scintillation crystals for PET

Abstract The suitability of monolithic Lutetium Fine Silicate (LFS) continuous scintillation crystals coupled to 64-channel SiPM-TSV matrices for small animal PET has been evaluated. Three crystals of size 25.8 × 25 . 8 × 15 mm 3 were tested: LYSO white coating, LFS white coating (LFS-W) and LFS specular coating (LFS-S). Electronically collimated measurements were carried out to compare the performance of LYSO and LFS crystals. Mean energy resolutions of 14%, 17% and 19% were measured for LYSO, LFS-S and LFS-W respectively. Similar intrinsic spatial resolutions were found for all three crystals in the central region. Different versions of the light model used to estimate the interaction position of the photons in the detector have been studied. Further measurements with two detector heads of each crystal type in coincidence have also been carried out with a moveable 22Na source. A ML-MLEM image reconstruction code is used to reconstruct the data. Final position resolutions for all three configurations show similar values. Taking into account that LYSO and LFS present similar performance levels (and considering that LFS has better timing resolution than LYSO) we conclude that LFS is a valid substitute for LYSO.

Design of a new tracking device for on-line beam range monitor in carbon therapy

Charged particle therapy is a technique for cancer treatment that exploits hadron beams, mostly protons and carbon ions. A critical issue is the monitoring of the beam range so to check the correct dose deposition to the tumor and surrounding tissues. The design of a new tracking device for beam range real-time monitoring in pencil beam carbon ion therapy is presented. The proposed device tracks secondary charged particles produced by beam interactions in the patient tissue and exploits the correlation of the charged particle emission profile with the spatial dose deposition and the Bragg peak position. The detector, currently under construction, uses the information provided by 12 layers of scintillating fibers followed by a plastic scintillator and a pixelated Lutetium Fine Silicate (LFS) crystal calorimeter. An algorithm to account and correct for emission profile distortion due to charged secondaries absorption inside the patient tissue is also proposed. Finally detector reconstruction efficiency for charged particle emission profile is evaluated using a Monte Carlo simulation considering a quasi-realistic case of a non-homogenous phantom.

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.

Performance of Scintillation Pixel Detectors with MPPC Read-out and Digital Signal Processing

We have assembled and tested a system of 2 detector modules containing Lutetium Fine Silicate scintillator pixels in 4 × 4 matrix, read out by multi-pixel photon counter arrays with the matching element size. The amplified signals were acquired using fast digitizers and stored for offline analysis. Using two different approaches, we have determined the single crystal relative energy resolution at 511 keV to be 14% and 12%. The coincidence time resolution has been tested using the digital constant fraction triggering and the leading edge method, and the resulting resolutions are 1.6 ns and 0.5 ns, respectively.

A crystal identification method for monolithic phoswich detectors based on scintillation light distribution

Phoswich detectors based on scintillation crystals are widely diffused for both PET and SPECT applications. In order to separate the signals arising from different layers many methods have been proposed in literature. Separation of the layers commonly relies on time discrimination or pulse height discrimination. In this work, by means of experimental measurement on a phoswich detector based on Lanthanum Bromide and Lutetium Fine Silicate monolithic crystals, a novel method allowing to separate signals coming from different layers has been evaluated. The main feature of this method, specifically developed for phoswich based on monolithic scintillation crystals, is the discrimination capability based on the scintillation light distribution shape. For this reason, the findings that will be shown could be easily extended to whatever combination of scintillator, independently from their decay time or light yield.

Design of a tracking device for on-line dose monitoring in hadrontherapy

Hadrontherapy is a technique for cancer treatment that exploits ion beams (mostly protons and carbons). A critical issue is the accuracy that is achievable when monitoring the dose released by the beam to the tumor and to the surrounding tissues. We present the design of a tracking device, developed in the framework of the INSIDE project [1], capable of monitoring in real time the longitudinal profile of the dose delivered in the patient. This is possible by detecting the secondary particles produced by the interaction of the beam in the tissues. The position of the Bragg peak can be correlated to the charged particles emission point distribution measurement. The tracking device will be able to provide a fast response on the dose pattern by tracking the secondary charged fragments. The tracks are detected using 6 planes of scintillating fibers, providing the 3D coordinates of the track intersection with each plane. The fibers planes are followed by a plastic scintillator and by a small calorimeter built with a pixelated Lutetium Fine Silicate (LFS) crystal. A complete detector simulation, followed by the event reconstruction, has been performed to determine the achievable monitoring spatial resolution.

Timing measurements of lutetium based scintillators combined with silicon photomultipliers for TOF-PET system

As time-of-flight PET (TOF-PET) gains popularity in clinical diagnostic, the coincidence timing resolution of PET systems becomes more crucial. The most common scintillators for commercial TOF-PET systems are Lu-based ones such as LSO or LYSO for their high light output, high density and fast decay time. Recently, LGSO with 0.025% Ce (LGSO-fast) was developed which has faster decay time than LGSO with Ce concentration of 0.1 mol% (LGSO-standard). Using the LGSO-fast in conjunction with silicon photomultiplier (Si-PM) may improve the timing performance for the development of TOF-PET systems. Consequently, we tested the basic performance of LGSO-fast and coupled them with Si-PMs to measure the coincidence timing resolution using a high bandwidth digital oscilloscope. The performance was also evaluated for LGSO-standard and other Lu-based scintillators such as lutetium fine silicate (LFS) and two types of LYSOs from other manufacturers. The light output was largest for one of the LYSO from one manufacture and smallest for the LYSO from other manufacture. Decay time was fastest for LGSO-fast (33.8 ns) and slowest for one of the LYSO (39.9 ns). Coincidence timing resolution for 2.9 mm long Lu-based scintillators, LGSO-fast was the best (156.5 ps) and one of the LYSO showed the worst (235.1 ps). For the 20 mm long scintillators, coincidence timing resolution was also best for LGSO-fast (273.2 ps) and worst for one of the LYSO (481.8 ps). We conclude that LGSO-fast combined with Si-PM showed best timing performance among measured Lu-based scintillators. Also within the same Lu-based scintillators such as LYSOs, we found that the performance differences were sometimes significant and quality control of the Lu-based scintillator is essential to achieve good performance in PET systems.

Development of compact radiation detectors based on MAPD photodiodeswith Lutetium Fine Silicate and stilbene scintillators

Results of gamma-ray measurements taken with Lutetium Fine Silicate (LFS) scintillators and Micro-Pixel Avalanche Photodiodes (MAPD) are presented in the energy range of 59.6 keV to 834.8 keV . Dependences of energy resolution on gamma-ray energy are studied. Results of several measurements are discussed to assess the performance of gamma ray source identification of the developed detector. The alpha particle and neutron detection performance of LFS and stilbene scintillators coupled to micro-pixel avalanche photodiode are discussed as well.

Alpha particle detector based on micropixel avalanche photodiodes

The main goal of this work is to study the possibility of detecting alpha particles with a micropixel avalanche photodiode (MAPD) in combination with Lutetium Fine Silicate (LFS) scintillators (500 μm thick). The results show that alpha detectors based on the MAPD are expected to be useful in many applications: public security (associated particle imaging for explosives and drugs detection), radioactive contamination monitoring in various environments, and detection of charged particles from nuclear reactions.

Measurement on properties of MPPC for TOF-PET system

A large number of techniques are rapidly being developed for the diagnosis of cancer, including time-of-flight positron-emission tomography (TOF-PET). To construct an effective TOF-PET system, we introduced lutetium fine silicate (LFS) as a scintillator and a multi-pixel photon counter (MPPC) as a photosensor that exhibits a rapid response. In this study, we investigated four types of MPPCs with a sensitive area of 1 × 1 mm2 sensitive area and different pitch sizes. All MPPCs showed a timing resolution of 72 ps at the full-width at half-maximum with operating voltages of dV ∼ 3V (with the exception of the 100-pixels MPPC).

Micropixel avalanche photodiodes and the possibility for their application in positron-emission tomography

Micropixel avalanche photodiodes (MAPDs) are new instruments for detecting low-intensity light. They consist of many microcounters (pixels integrated on a common silicon wafer). A unique design by the Joint Institute for Nuclear Research (JINR) (Z. Sadygov)—deep-microwell MAPD—provides an order of larger pixel densities without losses in photon-detection efficiency. These instruments are beginning to find use in precision electromagnetic calorimetry. MAPDs can be most widely applied as photodetectors in scanners for positron-emission tomographs (PETs), particularly the time-of-flight PETs becoming popular now. The possibility of using MAPDs in PETs is shown, and the time resolution of a pair of quanta detected by Lutetium Fine Silicate scintillation crystals with MAPD readout is obtained at the level of 400 ps.