Multi-anode Photomultiplier Tube Research Articles

Real‐time scintillation array dosimetry for radiotherapy: The advantages of photomultiplier detectors

In this paper, a photomultiplier tube (PMT) array dosimetry system has been developed and tested for the real-time readout of multiple scintillation signals from fiber optic dosimeters. It provides array dosimetry with the advantages in sensitivity provided by a PMT, but without the need for a separate PMT for each detector element. The PMT array system consisted of a multianode PMT, a multichannel data acquisition system, housing and optic fiber connections suitable for clinical use. The reproducibility, channel uniformity, channel crosstalk, acquisition speed, and sensitivity of the PMT array were quantified using a constant light source. Its performance was compared to other readout systems used in scintillation dosimetry. An in vivo HDR brachytherapy treatment was used as an example of a clinical application of the dosimetry system to the measurement of dose at multiple sites in the rectum. The PMT array system was also tested in the pulsed beam of a linear accelerator to test its response speed and its application with two separate methods of Cerenkov background removal. The PMT array dosimetry system was highly reproducible with a measurement uncertainty of 0.13% for a 10 s acquisition period. Optical crosstalk between neighboring channels was accounted for by omitting every second channel. A mathematical procedure was used to account for the crosstalk in next-neighbor channels. The speed and sensitivity of the PMT array system were found be superior to CCD cameras, allowing for measurement of more rapid changes in dose rate. This was further demonstrated by measuring the dose delivered by individual photon pulses of a linear accelerator beam. The PMT array system has advantages over CCD camera-based systems for the readout of scintillation light. It provided a more sensitive, more accurate, and faster response to meet the demands of future developments in treatment delivery.

Four Channel, 40 ps Resolution, Fully Integrated Time-to-Amplitude Converter for Time-Resolved Photon Counting

Recently, a growing interest has arisen about the time-correlated single photon counting (TCSPC) technique, that allows the analysis of fast and weak light waveforms with a time resolution in the picosecond order. Since TCSPC basically consists of the measurement of the arrival time of a photon, a high resolution and high linearity time measurement block is of the utmost importance; moreover, the use of multianode Photo Multiplier Tube and of single photon avalanche diode arrays led to the development of multichannel acquisition systems, where the time measurement block has to be integrated to reduce both cost and area. We have designed and fabricated a four channel fully integrated time-to-amplitude converter (TAC), built in 0.35 μm Si-Ge technology, characterized by an excellent time resolution (less than 50 ps full width half maximum), low differential nonlinearity (better than 0.02 LSB peak-peak and 0.0003 LSB rms), high counting rate (16 MHz), low and constant power dissipation (50 mW) and low area occupation (2.58 × 1.28 mm2 ). Moreover, the very low crosstalk ( -115 dB) between channels, together with low power and low area makes the converter suitable for large scale multi-channel acquisition chains.

Small animal PET scanner based on monolithic LYSO crystals: Performance evaluation

The authors have developed a small animal Positron emission tomography (PET) scanner based on monolithic LYSO crystals coupled to multi-anode photomultiplier tubes (MA-PMTs). In this study, the authors report on the design, calibration procedure, and performance evaluation of a PET system that the authors have developed using this innovative nonpixelated detector design. The scanner is made up of eight compact modules forming an octagon with an axial field of view (FOV) of 40 mm and a transaxial FOV of 80 mm diameter. In order to fully determine its performance, a recently issued National Electrical Manufacturers Association (NEMA) NU-4 protocol, specifically developed for small animal PET scanners, has been followed. By measuring the width of light distribution collected in the MA-PMT the authors are able to determine depth of interaction (DOI), thus making the proper identification of lines of response (LORs) with large incidence angles possible. PET performances are compared with those obtained with currently commercially available small animal PET scanners. At axial center when the point-like source is located at 5 mm from the radial center, the spatial resolution measured was 1.65, 1.80, and 1.86 mm full width at half maximum (FWHM) for radial, tangential, and axial image profiles, respectively. A system scatter fraction of 7.5% (mouse-like phantom) and 13% (rat-like phantom) was obtained, while the maximum noise equivalent count rate (NECR) was 16.9 kcps at 12.7 MBq (0.37 MBq/ml) for mouse-like phantom and 12.8 kcps at 12.4 MBq (0.042 MBq/ml) for rat-like phantom The peak absolute sensitivity in the center of the FOV is 2% for a 30% peak energy window. Several animal images are also presented. The overall performance of our small animal PET is comparable to that obtained with much more complex crystal pixelated PET systems. Moreover, the new proposed PET produces high-quality images suitable for studies with small animals.

Small prototype gamma camera based on wavelength-shifting fibres

We are studying and developing a small field of view gamma camera based on wavelength-shifting optical fibres coupled to both sides of an inorganic scintillation crystal and using for the light readout highly sensitive photon detectors, namely silicon photomultipliers (SiPMs) and high efficiency multi-anode photomultiplier tubes (MaPMTs). The coupling of the fibres in orthogonal directions allows obtaining 2D position information, while the energy signal is provided by a PMT. A first prototype laboratory system has been developed using a custom-made 50 × 50 × 3 mm3 CsI(Na) crystal with embedded 1 mm diameter fibres and reading out the light from several fibres in each direction, both with individual SiPMs and with a MaPMT. Proof-of-concept studies and results obtained with these systems using 57Co are presented and compared. The application of optical fibres combined with highly sensitive SiPMs or MaPMTs as light sensors in a compact gamma camera has the potential to improve the spatial resolution to the 1-2 mm FWHM level, thus improving the sensitivity of typical scintigraphy techniques and making such camera clinically useful. Results demonstrate the feasibility and imaging capability of the system using both types of photon detectors for imaging. In the case of SiPMs, a temperature cooling system is necessary to improve the SNR and consequently achieve a better imaging performance. The development of larger prototypes with 10 × 10 cm2 and 12 × 12 cm2 is under way, using 1 mm2 SiPMs and 64 anode PMTs, respectively.

Photon Detection Systems for Modern Cherenkov Detectors

Abstract Modern experiments in hadronic physics require detector systems capable of identifying and reconstructing all final–state particle and their momentum vectors. The ANDA experiment at FAIR and the CLAS 12 experiment and Jefferson Laboratory both plan to use imaging Cherenkov counters for particle identification. CLAS 12 will feature a Ring Imaging CHerenkov counter (RICH), while ANDA plans to construct Cherenkov counters relying on the Detections of Internally Reflected Cherenkov light (DIRC). These detectors require high–rate, single–photon capable light detection systems with sufficient granularity and position resolution. Several candidate systems are available, ranging from multi–anode photomultiplier tubes to micro–channel plate systems to silicon photomultipliers. Each of these detection solutions has particular advantages and disadvantages. Detailed studies of the rate dependence, cross–talk, time–resolution and position resolution fro a range of commercially available photon detection solutions are presented and evaluated on their applicability to the ANDA and CLAS12 Cherenkov counters.

Position sensitive photon detectors for nuclear physics, particle physics and healthcare applications

Modern experiments in hadronic physics require detector systems capable of identifying and reconstructing all final-state particles and their momentum vectors. Imaging Cherenkov counters (RICH and DIRC) are frequently employed in nuclear and particle physics experiments. These detectors require high-rate, single-photon capable light detection system with sufficient granularity and position resolution. Several candidate systems are available, ranging from multi-anode photomultiplier tubes to micro-channel plate systems to silicon photomultipliers. Each of these detection solutions has particular advantages and disadvantages. Detailed studies of rate dependence, cross-talk, time-resolution and position resolution for a range of available photon detection solutions are presented. These properties make these photon detection systems ideal for radionuclide imaging applications. Cherenkov radiation can also be used for medical imaging applications. Two different applications using the Cherenkov effect for radionuclide imaging will be reviewed.

Research and development of a CBM-RICH prototype

We have developed a gaseous Ring Imaging CHerenkov detector prototype (PNU-RICH2) of the CBM-RICH detector. This prototype has the same radiator length as the planned CBM-RICH detector. The PNU-RICH2 includes a spherical concave mirror and 2 types of Multi-anode PMTs. The PNU-RICH2 detector has tested at the PAL-TEST LINAC with 60MeV electron beam. A detector performance from the beam test will be presented and discussed in comparison with simulation results.

Monte Carlo simulation of scintillation photons for the design of a high-resolution SPECT detector dedicated to human brain

In a typical single photon emission computed tomography (SPECT) system, intrinsic spatial resolution depends on the accuracy of the identification of an interacting point, which is dominated by propagation of the scintillation photons in the detector block. This study was intended to establish a Monte Carlo simulation-based evaluation tool taking into account the propagation of scintillation photons to estimate the intrinsic spatial and energy resolutions of the position-sensitive scintillator block in a SPECT detector. We employed Geant4 Monte Carlo simulation library which incorporated the optical photon processes for two different designs of the position-sensitive scintillator blocks. The validation of the simulation code was performed for a monolithic NaI(Tl) scintillator (251×147×6.4mm(3)) coupled to 15 flat-panel type multi-anode photo multiplier tubes (PMT) (H8500: Hamamatsu) and results were compared with those obtained experimentally. The code was then applied to a LaBr(3)(Ce) scintillator of 120mm square with varied thicknesses for designing high-resolution detector. The simulation resulted in 2.6mm full width at half maximum (FWHM) of spatial resolution and 9.0% FWHM of energy resolution for the NaI(Tl)-based detector, which were in a good agreement of the experimental results, i.e., 2.7mm and 10%, respectively. These findings suggest that Geant4 simulation including optical photon processes enables to predict the spatial and energy resolutions of a SPECT detector block accurately. The simulation also demonstrated that 2mm spatial resolution can be obtained for a 6mm thickness of the LaBr(3)(Ce), which is a significant improvement in performance as compared to existing gamma camera system that employs the scintillation detector fitted with PMTs. The Monte Carlo simulation-based evaluation tool was established to estimate the intrinsic spatial and energy resolutions of SPECT detector with position sensitive PMTs. This simulation may be useful to provide an optimal design of a SPECT detector without physical experiments.

A novel compensation method for the anode gain non-uniformity of multi-anode photomultiplier tubes

The position-sensitive multi-anode photomultiplier tube (MA-PMT) is widely used in high-resolution scintillation detectors. However, the anode gain non-uniformity of this device is a limiting factor that degrades the intrinsic performance of the detector module. The aim of this work was to develop a gain compensation method for the MA-PMT and evaluate the resulting enhancement in the performance of the detector. The method employs a circuit that is composed only of resistors and is placed between the MA-PMT and a resistive charge division network (RCN) used for position encoding. The goal of the circuit is to divide the output current from each anode, so the same current flows into the RCN regardless of the anode gain. The current division is controlled by the combination of a fixed-value series resistor with an output impedance that is much larger than the input impedance of the RCN, and a parallel resistor, which detours part of the current to ground. PSpice simulations of the compensation circuit and the RCN were performed to determine optimal values for the compensation resistors when used with Hamamatsu H8500 MA-PMTs. The intrinsic characteristics of a detector module consisting of this MA-PMT and a lutetium-gadolinium-oxyorthosilicate (LGSO) crystal array were tested with and without the gain compensation method. In simulation, the average coefficient of variation and max/min ratio decreased from 15.7% to 2.7% and 2.0 to 1.2, respectively. In the flood map of the LGSO-H8500 detector, the uniformity of the photopeak position for individual crystals and the energy resolution were much improved. The feasibility of the method was shown by applying it to an octagonal prototype positron emission tomography scanner.

Multianode photomultiplier tube studies for imaging applications

Highly efficient and position sensitive photon detection is essential in a variety of applications from particle identification in fundamental nuclear and particle physics research, to radionuclide imaging in healthcare. Due to their position sensitivity and high packing fraction, the Hamamatsu H8500 and H9500 multianode photomultiplier tubes (MAPMTs) are promising candidates for such applications and have thus been studied through precision laser scans at several light intensities. This has revealed signal and crosstalk dependencies upon constructional features of the MAPMTs. Both MAPMTs feature a common last dynode output signal, which can be used for self-triggering. The strength and timing of this signal have been investigated for the H8500 MAPMT, yielding similar dependencies upon MAPMT construction and standard deviation time resolutions of 67.5ps and 154.4ps for 20 and single photoelectron signals respectively.

Silicon photomultipliers for scintillating trackers

In recent years, silicon photomultipliers (SiPMs) have been proposed as a new kind of readout device for scintillating detectors in many experiments. A SiPM consists of a matrix of parallel-connected pixels, which are independent photon counters working in Geiger mode with very high gain (∼106). This contribution presents the use of an array of eight SiPMs (manufactured by FBK-irst) for the readout of a scintillating bar tracker (a small size prototype of the Electron Muon Ranger detector for the MICE experiment). The performances of the SiPMs in terms of signal to noise ratio, efficiency and time resolution will be compared to the ones of a multi-anode photomultiplier tube (MAPMT) connected to the same bars. Both the SiPMs and the MAPMT are interfaced to a VME system through a 64 channel MAROC ASIC.

National Electrical Manufacturers Association NU-4 Performance Evaluation of the PET Component of the NanoPET/CT Preclinical PET/CT Scanner

The NanoPET/CT represents the latest generation of commercial preclinical PET/CT systems. This article presents a performance evaluation of the PET component of the system according to the National Electrical Manufacturers Association (NEMA) NU-4 2008 standard. The NanoPET/CT consists of 12 lutetium yttrium orthosilicate:cerium modular detectors forming 1 ring, with 9.5-cm axial coverage and a 16-cm animal port. Each detector crystal is 1.12 × 1.12 × 13 mm, and 1 module contains 81 × 39 of these crystals. An optical light guide transmits the scintillation light to the flat-panel multianode position-sensitive photomultiplier tubes. Analog-to-digital converter cards and a field-programmable gate array-based data-collecting card provide the readout. Spatial resolution, sensitivity, counting rate capabilities, and image quality were evaluated in accordance with the NEMA NU-4 standard. Energy and temporal resolution measurements and a mouse imaging study were performed in addition to the standard. Energy resolution was 19% at 511 keV. The spatial resolution, measured as full width at half maximum on single-slice rebinning/filtered backprojection-reconstructed images, approached 1 mm on the axis and remained below 2.5 mm in the central 5-cm transaxial region both in the axial center and at one-quarter field of view. The maximum absolute sensitivity for a point source at the center of the field of view was 7.7%. The maximum noise equivalent counting rates were 430 kcps at 36 MBq and 130 kcps at 27 MBq for the mouse- and rat-sized phantoms, respectively. The uniformity and recovery coefficients were measured with the image-quality phantom, giving good-quality images. In a mouse study with an (18)F-labeled thyroid-specific tracer, the 2 lobes of the thyroid were clearly distinguishable, despite the small size of this organ. The flexible readout system allowed experiments to be performed in an efficient manner, and the system remained stable throughout. The large number of detector crystals, arranged with a fine pitch, results in excellent spatial resolution, which is the best reported for currently available commercial systems. The absolute sensitivity is high over the field of view. Combined with the excellent image quality, these features make the NanoPET/CT a powerful tool for preclinical research.

Design Considerations for the Next-Generation MAPMT-Based Monolithic Scintillation Camera.

Multi-anode photomultiplier tubes (MAPMTs) offer high spatial resolution with their small size anodes that may range from 64 to 1024 in number per tube. In order to increase detector size, MAPMT modules can be arranged in arrays and combined in a single modular scintillation camera. However, then the large number of channels that require amplification and digitization become practically not feasible unless signals are combined or reduced in some manner. Conventional approaches use resistive charge division readouts with a centroid algorithm (or a variant of it) for simplicity in the electronic circuitry implementation and fast execution. However, coupling signals from many anodes may cause significant information loss and limit achievable resolution. In this study, a new approach for optimizing readout-electronics design for MAPMTs based on an analysis of information content in the signals is presented. An adaptive read-out scheme to be used with maximum-likelihood estimation methods is proposed. This scheme achieves precision in estimating event parameters that is close to what is achieved by retaining all signals.

Performance and applications of the UVscope instrument

Abstract UVscope is a portable multi-pixels photon detector developed at IASF-Pa to support experimental activities in the high-energy astrophysics and cosmic rays field. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300–650 nm. Thanks to its features and operational flexibility, the instrument can be used in a wide field of applications where the knowledge of the environmental luminosity is required, as in the characterization of sites for ground-based Cherenkov and fluorescence telescopes, and for cross-calibration of their cameras. The present version of UVscope is based on a Multi Anode Photo Multiplier Tube and it is completed by a motorized mount and a filter wheel which allow to make low-light measurements, at programmed pointing directions and at different filter wavelengths. In this paper, the instrument is firstly presented in all its components; then the procedures adopted for its absolute and relative calibration are detailed. The performance of UVscope is evaluated and, finally, current and planned scientific applications are described.

The track imaging Cherenkov experiment

We describe a dedicated cosmic-ray telescope that explores a new method for detecting Cerenkov radiation from high-energy primary cosmic rays and the large particle air shower they induce upon entering the atmosphere. Using a camera comprising 16 multi-anode photomultiplier tubes for a total of 256 pixels, the Track Imaging Cerenkov Experiment (TrICE) resolves substructures in particle air showers with 0.086 degree resolution. Cerenkov radiation is imaged using a novel two-part optical system in which a Fresnel lens provides a wide-field optical trigger and a mirror system collects delayed light with four times the magnification. TrICE records well-resolved cosmic-ray air showers at rates ranging between 0.01-0.1 Hz.

Development and Studies of Novel Microfabricated Radiation Hard Scintillation Detectors With High Spatial Resolution

A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with a liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal, and exchange making the active medium intrinsically radiation hard. Prototype detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read-out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{90}{\rm Sr}$</tex> </formula> yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.

In vivo dosimetric system based on Gallium Nitride radioluminescence

Abstract We propose an implantable dosimetric system for real-time measurements of dose and dose rate. It consists of a fiber probe and a spectrophotometric module with signal processing implementation. The probe incorporates a small GaN crystal bulk ( 3 ) used as radioluminescence (RL) transducer. The spectrophotometric module has been designed using a concave spherical grating and a multi-anode photomultiplier tube (PMT). The system has been tested in clinical conditions, using photon beams delivered by clinical linear accelerators (Clinac). Testing results show an excellent linear response and no significant angular dependence, and are in good agreement with those from a standard ionization chamber (IC).

Characterization of a rotating slat collimator system dedicated to small animal imaging

Some current investigations based on small animal models are dedicated to functional cerebral imaging. They represent a fundamental tool to understand the mechanisms involved in neurodegenerative diseases. In the radiopharmaceutical development approach, the main challenge is to measure the radioactivity distribution in the brain of a subject with good temporal and spatial resolutions. Classical SPECT systems mainly use parallel hole or pinhole collimators. In this paper we investigate the use of a rotating slat collimator system for small animal brain imaging. The proposed prototype consists of a 64-channel multi-anode photomultiplier tube (H8804, Hamamatsu Corp.) coupled to a YAP:Ce crystal highly segmented into 32 strips of 0.575 × 18.4 × 10 mm3. The parameters of the rotating slat collimator are optimized using GATE Monte Carlo simulations. The performance of the proposed prototype in terms of spatial resolution, detection efficiency and signal-to-noise ratio is compared to that obtained with a gamma camera equipped with a parallel hole collimator. Preliminary experimental results demonstrate that a spatial resolution of 1.54 mm can be achieved with a detection efficiency of 0.012% for a source located at 20 mm, corresponding to the position of the brain in the prototype field of view.

4π FOV compact Compton camera for nuclear material investigations

A compact Compton camera with a 4π field of view (FOV) was manufactured using the design parameters optimized with the effective choice of gamma-ray interaction order determined from a Monte Carlo simulation. The camera consisted of six CsI(Na) planar scintillators with a pixelized structure that was coupled to position sensitive photomultiplier tubes (H8500) consisting of multiple anodes connected to custom-made circuits. The size of the scintillator and each pixel was 4.4×4.4×0.5 and 0.2×0.2×0.5 cm, respectively. The total size of each detection module was only 5×5×6 cm and the distance between the detector modules was approximately 10 cm to maximize the camera performance, as calculated by the simulation. Therefore, the camera is quite portable for examining nuclear materials in areas, such as harbors or nuclear power plants. The non-uniformity of the multi-anode PMTs was corrected using a novel readout circuit. Amplitude information of the signals from the electronics attached to the scintillator-coupled multi-anode PMTs was collected using a data acquisition board (cDAQ-9178), and the timing information was sent to a FPGA (SPARTAN3E). The FPGA picked the rising edges of the timing signals, and compared the edges of the signals from six detection modules to select the coincident signal from a Compton pair only. The output of the FPGA triggered the DAQ board to send the effective Compton events to a computer. The Compton image was reconstructed, and the performance of the 4π FOV Compact camera was examined.

Status and perspectives of vacuum-based photon detectors

Vacuum-based photodetectors are one of the most promising devices to detect Cherenkov photons. This paper reviews recent developments of vacuum-based photodetectors, such as multi-anode photomultiplier tubes (MaPMTs), hybrid photodetectors (HPDs/HPADs) and micro-channel-plate PMTs (MCP-PMTs), in view of application to RICH detectors. Photodetectors with luminescent anode are also discussed. It is emphasized that, in the past several years, there has been significant progress in development of devices having improved quantum efficiency, immunity for the magnetic field, and timing resolution.