Multi-anode PMT Research Articles

The coordinate sensitive detector with high space and time resolution based on the MA-20 multianode PMT

The work is dedicated to the discussion of the possibility of creating a position-sensitive detector with high coordinate reconstruction. The paper presents the simulation results and the experimentally obtained data for a prototype detector based on the MA-20 multianode PMT [1] and a linear stack of scintillating crystal or plastic strips. The multianode position-sensitive PMT MA-20 has a semitransparent bi-alkaline photocathode with the size of the sensitive area of 10 × 200 mm2, 10 evaporated type bi-alkaline type dynodes of the same length, and 20 separated anodes. This PM is the invention of the authors. The maximum gain of the dynode system is 106. The stack of scintillating strips made of GSO (gadolinium orthosilicate) crystals with an element size of 3 × 10 × 50 mm3, of BGO (bismuth germanate) crystals with an element size of 5 × 15 × 40 mm3, and finally stack of strips made of a plastic scintillator with an element size of 5 × 10 × 200 mm3 were used for experimental measurement of a spatial resolution of the detector prototype. Space resolution was determined by the position of the center of gravity of charges of neighboring anodes [2]. As a source of radiation, the collimated 137Cs (γ 0.662 MeV) and 90Sr (β− 2.283 MeV) were used, the measured number of photoelectrons is 10–20 of one element of the stack, depending on the scintillating strip type. The use of a multi-anode photomultiplier in combination with the stack of crystal or plastic scintillators allows one to get a simple linear detector with high performance in spatial resolution and also with a low level of intrinsic noise in comparison, for example, with silicon PMT. A resolution simulation was performed for a system consisting of a one-dimensional stack of scintillation strips placed on the photocathode of a multi-anode PMT for different values of the strips width and the number of photoelectrons of one strip. The experimental dependences of the signal value versus position of optical fiber with a diameter of 1 mm on the photocathode of the 20 anodes PMT were also measured that allowed to specify the coordinate resolution for the described detector. As a result of processing the collected data, spatial resolution was obtained at the level of 1 mm. The obtained results are in good agreement with the simulation results.

Development of a Compton camera for prompt-gamma medical imaging

A Compton camera-based detector system for photon detection from nuclear reactions induced by proton (or heavier ion) beams is under development at LMU Munich, targeting the online range verification of the particle beam in hadron therapy via prompt-gamma imaging. The detector is designed to be capable to reconstruct the photon source origin not only from the Compton scattering kinematics of the primary photon, but also to allow for tracking of the secondary Compton-scattered electrons, thus enabling a γ-source reconstruction also from incompletely absorbed photon events. The Compton camera consists of a monolithic LaBr3:Ce scintillation crystal, read out by a multi-anode PMT acting as absorber, preceded by a stacked array of 6 double-sided silicon strip detectors as scatterers. The detector components have been characterized both under offline and online conditions. The LaBr3:Ce crystal exhibits an excellent time and energy resolution. Using intense collimated 137Cs and 60Co sources, the monolithic scintillator was scanned on a fine 2D grid to generate a reference library of light amplitude distributions that allows for reconstructing the photon interaction position using a k-Nearest Neighbour (k-NN) algorithm. Systematic studies were performed to investigate the performance of the reconstruction algorithm, revealing an improvement of the spatial resolution with increasing photon energy to an optimum value of 3.7(1)mm at 1.33MeV, achieved with the Categorical Average Pattern (CAP) modification of the k-NN algorithm.

Test of the photon detection system for the LHCb RICH Upgrade in a charged particle beam

The LHCb detector will be upgraded to make more efficient use of the available luminosity at the LHC in Run III and extend its potential for discovery. The Ring Imaging Cherenkov detectors are key components of the LHCb detector for particle identification. In this paper we describe the setup and the results of tests in a charged particle beam, carried out to assess prototypes of the upgraded opto-electronic chain from the Multi-Anode PMT photosensor to the readout and data acquisition system.

Design, development and evaluation of a resistor-based multiplexing circuit for a 20×20 SiPM array

One technical challenge in developing a large-size scintillator detector with multiple Silicon Photomultiplier (SiPM) arrays is to read out a large number of detector output channels. To achieve this, different signal multiplexing circuits have been studied and applied with different performances and cost-effective tradeoffs. Resistor-based multiplexing circuits exhibit simplicity and signal integrity, but also present the disadvantage of timing shift among different channels. In this study, a resistor-based multiplexing circuit for a large-sized SiPM array readout was developed and evaluated by simulation and experimental studies. Similarly to a multiplexing circuit used for multi-anode PMT, grounding and branching resistors were connected to each SiPM output channel. The grounding resistor was used to simultaneously reduce the signal crosstalk among different channels and to improve timing performance. Both grounding and branching resistor values were optimized to maintain a balanced performance of the event energy, timing, and positioning. A multiplexing circuit was implemented on a compact PCB and applied for a flat-panel detector which consisted of a 32×32 LYSO scintillator crystals optically coupled to 5×5 SiPM arrays for a total 20×20 output channels. Test results showed excellent crystal identification for all 1024 LYSO crystals (each with 2×2×30mm3 size) with 22Na flood-source irradiation. The measured peak-to-valley ratio from typical crystal map profile is around 3:1 to 6.6:1, an average single crystal energy resolution of about 17.3%, and an average single crystal timing resolution of about 2ns. Timing shift among different crystals, as reported in some other resistor-based multiplexing circuit designs, was not observed. In summary, we have designed and implemented a practical resistor-based multiplexing circuit that can be readily applied for reading out a large SiPM array with good detector performance.

A Compton camera prototype for prompt gamma medical imaging

A Compton camera prototype for a position-sensitive detection of prompt gamma rays from proton-induced nuclear reactions is being developed in Garching. The detector system allows to track the Compton-scattered electrons. The camera consists of a monolithic LaBr3:Ce scintillation absorber crystal, read out by a multi-anode PMT, preceded by a stacked array of 6 double-sided silicon strip detectors acting as scatterers. The LaBr3:Ce crystal has been characterized with radioactive sources. Online commissioning measurements were performed with a pulsed deuteron beam at the Garching Tandem accelerator and with a clinical proton beam at the OncoRay facility in Dresden. The determination of the interaction point of the photons in the monolithic crystal was investigated.

AMIGA at the Pierre Auger Observatory: The interface and control electronics of the first prototype muon counters

AMIGA is an enhancement of the Pierre Auger Observatory. The main goals of AMIGA are to extend the full efficiency range to lower energies of the Observatory and to measure the muon content of extensive air showers. Currently, it consists of 61 detector pairs, each one composed of a surface water-Cherenkov detector and a buried muon counter. Prototypes of the muon counter – buried at a depth of 2.25m – were installed at each vertex of a hexagon and at its center with 750m spacing. Each prototype has a detection area of 10m2 segmented in 64 scintillation strips and coupled to a multi-anode PMT through optical fibers. The electronic systems of these prototypes are accessible via a service tube. An electronics interface and control board were designed to extract the data from the counter and to provide a remote control of the system. This article presents the design of the interface and control board and the results and performance during the first AMIGA acquisition period in 2012.

Design and Performance of a High Spatial Resolution, Time-of-Flight PET Detector

This paper describes the design and performance of a high spatial resolution PET detector with time-of-flight capabilities. With an emphasis on high spatial resolution and sensitivity, we initially evaluated the performance of several 1.5 × 1.5 and 2.0 × 2.0 mm2 and 12-15 mm long LYSO crystals read out by several appropriately sized PMTs. Experiments to evaluate the impact of reflector on detector performance were performed and the final detector consisted of a 32 × 32 array of 1.5 × 1.5 × 15 mm3 LYSO crystals packed with a diffuse reflector and read out by a single Hamamatsu 64 channel multi-anode PMT. Such a design made it compact, modular and offered a cost-effective solution to obtaining excellent energy and timing resolution. To minimize the number of readout signals, a compact front-end readout electronics that summed anode signals along each of the orthogonal directions was also developed. Experimental evaluation of detector performance demonstrates clear discrimination of the crystals within the detector. An average energy resolution (FWHM) of 12.7 ± 2.6% and average coincidence timing resolution (FWHM) of 348 ps was measured, demonstrating suitability for use in the development of a high spatial resolution time-of-flight scanner for dedicated breast PET imaging.

Dual isotope imaging with LaBr3:Ce crystal and H8500 PSPMT

The introduction of Lanthanum Bromide crystal, characterized by a fast and high light emission, offers the possibility to improve both imaging spatial resolution and energy resolution in SPECT in the 80–300 kev energy range, without compromising detection efficiency. The expected performances may be limited if the crystal is used with a multi-anode PMT with Position Sensitive response due to the wide differences in the segmented anode pad gains, ranging from 2:1 to 10:1, . These characteristics may strongly deteriorate the overall energy resolution and, consequently, impair the detector imaging capability. For this reason, a 256 independent channel electronic read out was developed, based on an FPGA control, to individually read the charge on each anode. The electronics features a very low electronic noise ( < 1%) and a wide dynamic range. The readout electronics was used to build a gamma camera based on a single 100 mm × 100 mm continuous LaBr3:Ce crystal coupled to a 2 × 2 array SBA photocatode (38{%} QE) Hamamatsu H8500. An offline calibration procedure is also shown in order to compensate the anode gain variation and to exploit the LaBr3:Ce capabilities, obtaining on the whole detection area an 8.0–8.5{%} energy resolution at 140 kev. The high energy resolution performances of this gamma camera permitted to discriminate emissions from two different isotope ( Tc99m and Co57) with very close photon energy (140 and 122 kev respectively). This capability can be used to provide the gamma image with references coming from Co57 point sources (marker) fixed at known positions. These results confirm the LaBr3:Ce crystals as one of the most interesting for all single photon emission applications.

A position-sensitive detector with lithium glass and MaPMT

A position-sensitive detector is designed for neutron detection. It uses a single continuous screen of a self-made lithium glass scintillator, rather than discrete crystal implementations, coupling with a multi-anode PMT (MaPMT). The scintillator is fast and efficient; with a decay time of 34 ns and thermal neutron detection efficiency of around 95.8% for the 3 mm thick screen, and its light yield is around 5670 photons per neutron and 3768 photons per MeV γ rays deposition. The spatial resolution is around 1.6 mm (FWHM) with the energy resolution around 34.7% by using α (5.2 MeV) rays test.

A feasibility study on the use of arrays of discrete SiPMs for MR compatible LYSO readout using Monte Carlo simulation

This paper shows a feasibility study on the use of discrete SiPMs to read out monolithic scintillator-based detectors for use in molecular imaging applications. Monte Carlo simulations are carried out in order to evaluate the basic performance of 8 × 8 arrays of discrete SiPMs with different PDE values and compare it to conventional 64 channel multi-anode PMT (MA-PMT) readout. A detailed optical transport model was incorporated into the Monte Carlo simulation and a detector module based on a monolithic scintillator crystal of 50 × 50 × 4 mm3 coupled to a MA-PMT was built for experimental validation. The effect of the SiPM dynamic range was also investigated by including a model of the saturation effects into the optical transport simulation. The results show that a detector module based on an array of 8 × 8 discrete SiPM devices (3 × 3 mm2 and PDE > 32%) is feasible as a replacement of a 64 channel MA-PMT in order to read out large monolithic crystals for MR-compatible gamma cameras.

Resolution Properties of a Prototype Continuous Miniature Crystal Element (cMiCE) Scanner.

Continuous miniature crystal element (cMiCE) detectors are a potentially lower cost alternative for high resolution discrete crystal PET detector designs. We report on performance characteristics of a prototype PET scanner consisting of two cMiCE detector modules. Each cMiCE detector is comprised of a 50 × 50 × 8 mm3 LYSO crystal coupled to a 64 channel multi-anode PMT. The cMiCE detectors use a statistics-based positioning method based upon maximum likelihood estimation for event positioning. By this method, cMiCE detectors can also provide some depth of interaction event positioning information. For the prototype scanner, the cMiCE detectors were positioned across from one another on a horizontal gantry with a detector spacing of 10.7 cm. Full tomographic data were collected and reconstructed using single slice rebinning and filtered back projection with no smoothing. The average image resolutions in X (radial), Y (transverse) and Z (axial) were 1.05 ± 0.08 mm, 0.99 ± 0.07 mm, 1.24 ± 0.31 mm FWHM. These initial imaging results from a prototype imaging system demonstrate the outstanding image resolution performance that can be achieved using the potentially lower cost cMiCE detectors.

Dual Modality Ultrasound-SPET Detector for Molecular Imaging

We present an innovative compact dual-modality detector, which integrates an ultrasound probe with a scintigrafic γ -camera for molecular imaging in medicine, in order to get both morphological and functional information in a single three-dimensional image. The scintigraphic detector consists of a 2 × 2 array of a multi-anode PMT Hamamatsu H8500-Mod8 and a 4.0 mm thick continuous LaBr 3 (Ce) crystal equipped with four segment slant-hole collimators for single photon imaging (SPET). The collimator permits to recover the depth of a lesion by rotating around its vertical axis (z) without the need of rotating the camera around the investigated object. This detector can take advantage from being positioned close to the object and overcome the intrinsic limitations in spatial resolution arising from the geometry of SPET/CT gantry. The aim of this work is to describe preliminary phantom analysis and to provide a 3D US/SPET image.

FPGA Based Electronics for PET Detector Modules With Neural Network Position Estimators

We are currently developing a prototype monolithic scintillator PET detector module based on neural network position estimators. The detector module comprises a 25.5 mm × 25.5 mm × 10 mm LYSO crystal coupled to a Hamamatsu 64 channels multi-anode PMT H7546B. The electronics for the detector module reads out all the signal channels, which represents the distribution of the scintillating light for each 7 event, and calculates the impinging position according to the pre-defined neural network algorithms if the event satisfies the energy and timing selection conditions. Compared with classical pixelated detectors, a monolithic scintillator based detector module features a simpler design, lower cost, and better energy resolution, but has lower signal to noise ratio and a more complicated signal readout scheme and data processing. By Monte-Carlo simulation, the performances of several readout schemes were compared. An optimized readout scheme which combines the 64 channels into 16 digitized signals was adopted in our electronics design. After the high resolution signal waveform digitization, an FPGA takes charge of the remaining digital signal processing, including the on-line hardware execution of the neural network positioning algorithms. We have implemented the electronics system for the detector modules. A pipelined implementation of the optimized neural network algorithms in the FPGA is able to process up to 15.3 M events per second without loss of performance compared to an off-line implementation. In addition to the function validation tests, the preliminary performance of the detector module we are building for a PET system is also reported.

MAROC, a generic photomultiplier readout chip

The MAROC ASICs family is dedicated to the readout of 64-channel Multi Anode PMT and similar detectors. Its main roles are to correct the gain spread of MAPMT channels thanks to an individual variable gain preamplifier and to discriminate the input signals (from 50fC i.e 1/3 photo-electron) in order to produce 64 trigger outputs. A multiplexed analog charge output is also available with a dynamic range around 10 pe ( ∼ 1.6 pC) and a 12 bit Wilkinson ADC is embedded. Three versions of this chip have been submitted. MAROC 2 is the production version for the ATLAS luminometer and MAROC3 is a version with lower dissipation and significant improvements concerning the charge (30 pe: ∼ 5 pC) and trigger (discrimination from 10fC). This third version showed very good characteristics that are presented here.

Investigation of a Multi-Anode Microchannel Plate PMT for Time-of-Flight PET

We report on an investigation of a mulit-anode microchannel plate PMT for time-of-flight PET detector modules. The primary advantages of an MCP lie in its excellent timing properties (fast rise time and low transit time spread), compact size, and reasonably large active area, thus making it a good candidate for TOF applications. In addition, the anode can be segmented into an array of collection electrodes with fine pitch to attain good position sensitivity. In this paper, we investigate using the Photonis Planacon MCP-PMT with a pore size of 10 µm to construct a PET detector module, specifically for time-of-flight applications. We measure the single electron response by exciting the Planacon with pulsed laser diode. We also measure the performance of the Planacon as a PET detector by coupling a 4 mm × 4 mm × 10 mm LSO crystal to individual pixel to study its gain uniformity, energy resolution, and timing resolution. The rise time of the Planacon is 440 ps with pulse duration of about 1 ns. A transit time spread of 120 ps FWHM is achieved. The gain is fairly uniform across the central region of the Planacon, but drops off by as much as a factor of 2.5 around the edges. The energy resolution is fairly uniform across the Planacon with an average value of 18.6±0.7% FWHM. While the average timing resolution of 252±7 ps FWHM is achieved in the central region of the Planacon, it degrades to 280±9 ps FWHM for edge pixels and 316±15 ps FWHM for corner pixels. We compare the results with measurements performed with a fast timing conventional PMT (Hamamatsu R-9800). We find that the R9800, which has significantly higher PDE, has a better timing resolution than the Planacon. Furthermore, we perform detector simulations to calculate the improvement that can be achieved with a higher PDE Planacon. The calculation shows that the Planacon can achieve significantly better timing resolution if it can attain the same PDE as the R-9800, while only a 30% improvement is needed to yield a similar timing resolution as the R-9800.

Note: Fully integrated time-to-amplitude converter in Si–Ge technology

Over the past years an always growing interest has arisen about the measurement technique of time-correlated single photon counting TCSPC), since it allows the analysis of extremely fast and weak light waveforms with a picoseconds resolution. Consequently, many applications exploiting TCSPC have been developed in several fields such as medicine and chemistry. Moreover, the development of multianode PMT and of single photon avalanche diode arrays led to the realization of acquisition systems with several parallel channels to employ the TCSPC technique in even more applications. Since TCSPC basically consists of the measurement of the arrival time of a photon, the most important part of an acquisition chain is the time measurement block, which must have high resolution and low differential nonlinearity, and in order to realize multidimensional systems, it has to be integrated to reduce both cost and area. In this paper we present a fully integrated time-to-amplitude converter, built in 0.35 μm Si-Ge technology, characterized by a good time resolution (60 ps), low differential nonlinearity (better than 3% peak to peak), high counting rate (16 MHz), low and constant power dissipation (40 mW), and low area occupation (1.38×1.28 mm(2)).

Design and simulation of a novel method for determining depth-of-interaction in a PET scintillation crystal array using a single-ended readout by a multi-anode PMT

PET detectors with depth-of-interaction (DOI) encoding capability allow high spatial resolution and high sensitivity to be achieved simultaneously. To obtain DOI information from a mono-layer array of scintillation crystals using a single-ended readout, the authors devised a method based on light spreading within a crystal array and performed Monte Carlo simulations with individual scintillation photon tracking to prove the concept. A scintillation crystal array model was constructed using a grid method. Conventional grids are constructed using comb-shaped reflector strips with rectangular teeth to isolate scintillation crystals optically. However, the authors propose the use of triangularly shaped teeth, such that scintillation photons spread only in the x-direction in the upper halves of crystals and in the y-direction in lower halves. DOI positions can be estimated by considering the extent of two-dimensional light dispersion, which can be determined from the multiple anode outputs of a position-sensitive PMT placed under the crystal array. In the main simulation, a crystal block consisting of a 29 × 29 array of 1.5 mm × 1.5 mm × 20 mm crystals and a multi-anode PMT with 16 × 16 pixels were used. The effects of crystal size and non-uniform PMT output gain were also explored by simulation. The DOI resolution estimated for 1.5 × 1.5 × 20 mm3 crystals was 2.16 mm on average. Although the flood map was depth dependent, each crystal was well identified at all depths when a corner of the crystal array was irradiated with 511 keV gamma rays (peak-to-valley ratio ∼9:1). DOI resolution was better than 3 mm up to a crystal length of 28 mm with a 1.5 × 1.5 mm2 or 2.0 × 2.0 mm2 crystal surface area. The devised light-sharing method allowed excellent DOI resolutions to be obtained without the use of dual-ended readout or multiple crystal arrays.

New Continuous Miniature Crystal Element (cMiCE) Detector Geometries.

Continuous miniature crystal element (cMiCE) detectors are a potentially lower cost alternative to high resolution discrete crystal designs. We report on the intrinsic spatial resolution performance for two cMiCE PET detector designs with depth of interaction (DOI) positioning capability. The first detector utilizes a 50 mm by 50 mm by 8 mm LYSO crystal coupled to a 64 channel, multi-anode PMT. It provides 4 layers of DOI information. The crystal has beveled edges along two of its sides to improve the detector packing when placed in a ring geometry. The second detector utilizes a 50 mm by 50 mm by 15 mm, rectangular LYSO crystal coupled to a 64 channel, multi-anode PMT. It provides up to 15 layers of DOI information. The average intrinsic X, Y spatial resolution for the 8 mm thick, truncated crystal detector was 1.33 +/- 0.31 mm FWHM (45.6 mm by 46.6 mm useful imaging area). The average DOI resolution was 3.5 +/- 0.22 mm. The average intrinsic X, Y spatial resolution for the 15 mm thick crystal detector was 1.74 +/- 0.35 mm FWHM (44.6 mm by 44.6 mm useful imaging area). In addition, the average DOI spatial resolution for 56 test points spanning a 26.4 mm by 12.2 mm region of the crystal was 4.80 +/- 0.36 mm. We believe the 8 mm thick truncated crystal design is suitable for mouse imaging while the 15 mm thick crystal design is more suited for human organ specific imaging systems (e.g., breast and brain).

Application of multi-pixel avalanche photodiodes operating in Geiger mode for scintillator pad detector read-out

Details of application of Si avalanche photodiode read-out for scintillator pad detector are discussed. The detection of charged particles using scintillator pads read-out with embedded WLS fiber is explored in many HEP experiments. The 12 cm×12 cm and 4 cm×4 cm scintillator counter design developed for LHC-b experiment [LHC-b Calorimeters Technical Design Report, CERN/LHCC/, 2000-0036] is being explored for the “OKA” experiment (Protvino) [V.F. Obraztsov, OKA: the experimental program with RF-separated K+-beam, KAON-05, Evanston, 2005, 〈 http://www.oka.ihep.su〉] aimed to K-meson rare decays study. Recently developed multi-pixel avalanche photodiodes operating in Geiger mode have definitive advantages with respect to conventional multi-anode PMT, i.e. larger quantum efficiency, compact detector design and small light losses, lower supply voltage. All this allows one to achieve a high light response of more than 100 photo-electrons per MIP with a simple and economical detector design. In this paper we describe characteristics of 3 batches of MRS APD, produced by the CPTA, Moscow [Center of Perspective Technologies and Apparatus (CPTA), Moscow; Photonique SA, Geneva 〈 http://www.photonique.ch〉]. We tested 3 types of photodiodes with a sensitive area of 1 mm 2 with 556 pixels, defining the noise counting rate and detection efficiency as a function of electronics threshold.

Pixellated NaI (Tl) Detector for Light Yield Nonproportionality Investigation

An 8 × 8 pixellated Nal(Tl) detector (1.7 cm × 1.7 cm × 1.0 cm) coupled to a multi anode PMT read out system was modeled to study the impact of light yield nonproportionality due to multiple photon scatterings and assess the contribution of delta rays in Nal(Tl) energy resolution. Geant4 simulation tool with modified nonproportional optical photons sampling routine was used in the study. A deconvolution technique was implemented to allow decoupling of the multiple photon scatterings contribution from the total energy resolution. Results from the simulation demonstrated that the effect of nonproportionality due to multiple photon scatterings is too small to be observed. However, the contribution of the delta rays was found to be a significant component of the evaluated Nal(Tl) energy resolution.