H8500 Position Sensitive Photomultiplier Tubes Research Articles

A QTC-based signal readout for position-sensitive multi-output detectors

A new signal readout method for position-sensitive multi-output detectors, such as those in high-energy spectroscopy measurement and nuclear imaging, was developed by combining the charge division circuit, summing circuit and charge-to-time conversion (QTC) circuit. The 64 outputs of a Hamamatsu H8500 position-sensitive photomultiplier tube were processed, and three digital pulses were generated. The widths of digital pulses were determined using the time-to-digital converter in an field programmable gate array. The energy and position information of incident γ-rays is estimated based on the proportionality between the width of digital pulses and input charge created by γ-photons. A prototype was built using discrete components and tested, and the energy and position resolutions were improved compared with that obtained with standard ADCs. This method greatly simplifies the front-end electronics and the digital interface. It enables a compact electronics system and an easy integration into an ASIC.

Development of an all-in-one gamma camera/CCD system for safeguard verification

For the purpose of monitoring and verifying efforts at safeguarding radioactive materials in various fields, a new all-in-one gamma camera/charged coupled device (CCD) system was developed. This combined system consists of a gamma camera, which gathers energy and position information on gamma-ray sources, and a CCD camera, which identifies the specific location in a monitored area. Therefore, 2-D image information and quantitative information regarding gamma-ray sources can be obtained using fused images. A gamma camera consists of a diverging collimator, a 22 × 22 array CsI(Na) pixelated scintillation crystal with a pixel size of 2 × 2 × 6 mm3 and Hamamatsu H8500 position-sensitive photomultiplier tube (PSPMT). The Basler scA640-70gc CCD camera, which delivers 70 frames per second at video graphics array (VGA) resolution, was employed. Performance testing was performed using a Co-57 point source 30 cm from the detector. The measured spatial resolution and sensitivity were 4.77 mm full width at half maximum (FWHM) and 7.78 cps/MBq, respectively. The energy resolution was 18% at 122 keV. These results demonstrate that the combined system has considerable potential for radiation monitoring.

Design and development of a high resolution animal SPECT scanner dedicated for rat and mouse imaging

A dedicated small-animal SPECT system, HiReSPECT, was designed and developed to provide a high resolution molecular imaging modality in response to growing research demands. HiReSPECT is a dual-head system mounted on a rotating gantry. The detection system is based on pixelated CsI(Na) scintillator crystals coupled to two Hamamatsu H8500 Position Sensitive Photomultiplier Tubes in each head. Also, a high resolution parallel-hole collimator is applied to every head. The dimensions of each head are 50mm×100mm, enabling sufficient transaxial and axial fields-of-view (TFOV and AFOV), respectively, for coverage of the entire mouse in single-bed position imaging. However, a 50mm TFOV is not sufficient for transaxial coverage of rats. To address this, each head can be rotated by 90 degrees in order to align the larger dimension of the heads with the short body axis, allowing tomographic data acquisition for rats. An innovative non-linear recursive filter was used for signal processing/detection. Resolution recovery was also embedded in the modified Maximum-Likelihood Expectation Maximization (MLEM) image reconstruction code to compensate for Collimator-Detector Response (CDR). Moreover, an innovative interpolation algorithm was developed to speed up the reconstruction code. The planar spatial resolution at the head surface and the image spatial resolutions were 1.7mm and 1.2–1.6mm, respectively. The measurements followed by post-processing showed that the observed count rate at 20% count loss is about 42kcps. The system sensitivity at the collimator surface for heads 1 and 2 were 1.32cps/µCi and 1.25cps/µCi, respectively. The corresponding values were 1.18cps/µCi and 1.02cps/µCi at 8cm distance from the collimator surfaces. In addition, whole-body scans of mice demonstrated appropriate imaging capability of the HiReSPECT.

A high resolution SPECT detector based on thin continuous LYSO

Single-photon emission computed tomography (SPECT) detectors with improved spatial resolution can be used to build multi-pinhole SPECT systems that have a higher sensitivity or a higher spatial resolution. In order to improve the spatial resolution we investigate the performance of a 2 mm thick continuous Lutetium Yttrium Orthosilicate (LYSO) scintillator and compare it to the performance of a 5 mm thick continuous NaI(Tl) scintillator. The advantages of LYSO are its high stopping power and its non-hygroscopicity. Drawbacks are the lower light output and the intrinsic radioactivity. The hypothesis of this study is that such a thin LYSO scintillator will have a small light spread and, as a consequence, will also have an improved spatial resolution when coupled to a Hamamatsu H8500 position sensitive photomultiplier tube. To optimize the spatial resolution and the useful detector area we used a mean nearest neighbor event-positioning method. Beam source measurements (99mTc, 140 keV) were done to investigate the energy resolution and the spatial resolution of both detectors. The effect of the intrinsic radioactivity of the LYSO scintillator in the energy window was quantified. The mean energy resolution is 9.3% for the NaI(Tl) scintillator and 21.3% for the LYSO scintillator. The LYSO spectrum shows an X-ray escape peak which decreases the detection efficiency with 9.1%. The spatial resolution of the LYSO detector (0.93 mm full width at half maximum (FWHM)) is superior to the spatial resolution of the NaI(Tl) detector (1.37 mm FWHM). The intrinsic radioactivity in the energy window (42% window centered at 140 keV) is low (125.6 cps, 0.024 cps mm−3). LYSO is a promising scintillator for small-animal SPECT imaging, where spatial resolution is more important than energy resolution.

The Experimental Study of Lanthanum Bromide Detector in the Gamma Ray Imaging

Cerium activated lanthanum bromide (LaBr3:Ce3+) scintillator crystal has shown very promising characteristics for high-resolution and high-sensitivity gamma ray imaging and spectrometric applications [1,2,. In this paper, we present some preliminary results of a compact gamma camera based on LaBr3:Ce3+ crystal. The detector module consists of a continuous LaBr3:Ce3+ crystal with a sensitive area of 50x50 mm2 and 5mm thickness coupling to a Hamamatsu H8500 position-sensitive photomultiplier tube (PSPMT). A compact multiplexed readout based on symmetric charge division circuit (SCD) was developed to reduce the 64 anode signal to 16 readout channels, and a resistive division network to reduce the readout channels from 16 to 4. The performance of the imaging detector module was tested using a 57Co source. The preliminary results showed that this detector module can achieve an effective field-of-view (FOV) of ~39x39 mm2 with a good intrinsic spatial resolution around 1.5mm and energy resolution of 9.2% at 122 keV.

PhytoBeta imager: a positron imager for plant biology

Several positron emitting radioisotopes such as 11C and 13N can be used in plant biology research. The 11CO2 tracer is used to facilitate plant biology research toward optimization of plant productivity, biofuel development and carbon sequestration in biomass. Positron emission tomography (PET) imaging has been used to study carbon transport in live plants using 11CO2. Because plants typically have very thin leaves, little medium is present for the emitted positrons to undergo an annihilation event. The emitted positrons from 11C (maximum energy 960 keV) could require up to approximately 4 mm of water equivalent material for positron annihilation. Thus many of the positrons do not annihilate inside the leaf, resulting in limited sensitivity for PET imaging. To address this problem we have developed a compact beta-positive, beta-minus particle imager (PhytoBeta imager) for 11CO2 leaf imaging. The detector is based on a Hamamatsu H8500 position sensitive photomultiplier tube optically coupled via optical grease to a 0.5 mm thick Eljen EJ-212 plastic scintillator. The detector is equipped with a flexible arm to allow its placement and orientation over or under the leaf to be studied while maintaining the leaf's original orientation. To test the utility of the system the detector was used to measure carbon translocation in a leaf of the spicebush (Lindera benzoin) under two transient light conditions.

Performance evaluation of a parallel-hole collimated detector module for animal SPECT imaging

We have built and investigated a detector module for animal SPECT imaging, especially for use in large field of view (FOV) conditions. The module consists of a PMT-based detector and a parallel-hole collimator with an effective area of 80 mm×80 mm. The detector is composed of a NaI scintillation crystal array coupled to four H8500 position sensitive photomultiplier tubes (PS-PMT). The intrinsic energy resolution of the detector is 11.5% at 140 keV on average. The planar spatial resolution of the module changes from 2.2 mm to 5.1 mm at different source-to-collimator distances with an unchanged sensitivity of about 34cps/MBq. Additionally, the SPECT Micro Deluxe Phantom imaging was performed with a radius of rotation (ROR) of 40 mm. Using the FBP reconstruction algorithm, a high performance image was obtained, indicating the feasibility of this detector module.

Tomographic evaluation of a dual-head positron emission tomography system

In this paper we present the performance evaluation results, in the planar and tomographic modes, of a low-cost positron emission tomography camera dedicated to small-animal imaging. The system consists of two pixelated Lu2SiO5 crystals, two Hamamatsu H8500 position sensitive photomultiplier tubes, fast amplification electronics and an FPGA-USB-based read-out system. The parameters that have been studied are (i) saturation as a function of the head distance and photon acceptance angle, (ii) effect of the number of projections and half or complete head's rotation, (iii) spatial resolution as a function of the head distance, (iv) spatial resolution as a function of acceptance angle, (v) system's sensitivity as a function of these parameters and (vi) performance in small mice imaging. Image reconstruction has been carried out using open source software developed by our group (QSPECT), which is designed mainly for SPECT imaging. The results indicate that the system has a linear response for activities up to at least 2 MBq, which are typical in small-animal imaging. Best tomographic spatial resolution was measured to be ∼2 mm. The system has been found suitable for imaging of small mice both in the planar and tomographic modes.

Investigation of high resolution compact gamma camera module based on a continuous scintillation crystal using a novel charge division readout method

The objective of this study is to investigate a high performance and lower cost compact gamma camera module for a multi-head small animal SPECT system. A compact camera module was developed using a thin Lutetium Oxyorthosilicate (LSO) scintillation crystal slice coupled to a Hamamatsu H8500 position sensitive photomultiplier tube (PSPMT). A two-stage charge division readout board based on a novel sub-tractive resistive readout with a truncated center-of-gravity (TCOG) positioning method was developed for the camera. The performance of the camera was evaluated using a flood 99mTc source with a four-quadrant bar-mask phantom. The preliminary experimental results show that the image shrinkage problem associated with the conventional resistive readout can be effectively overcome by the novel subtractive resistive readout with an appropriate fraction subtraction factor. The response output area (ROA) of the camera shown in the flood image was improved up to 34%, and an intrinsic spatial resolution better than 2 mm of detector was achieved. In conclusion, the utilization of a continuous scintillation crystal and a flat-panel PSPMT equipped with a novel subtractive resistive readout is a feasible approach for developing a high performance and lower cost compact gamma camera.

Performance Characteristics of BGO Detectors for a Low Cost Preclinical PET Scanner

PETbox is a low-cost benchtop PET scanner dedicated to high throughput preclinical imaging that is currently under development at our institute. This paper presents the design and characterization of the detectors that are used in the PETbox system. In this work, bismuth germanate scintillator was used for the detector, taking advantage of its high stopping power, high photoelectric event fraction, lack of intrinsic background radiation and low cost. The detector block was segmented into a pixelated array consisting of 20 × 44 elements, with a crystal pitch of 2.2 mm and a crystal cross section of 2 mm × 2 mm. The effective area of the array was 44 mm × 96.8 mm. The array was coupled to two Hamamatsu H8500 position sensitive photomultiplier tubes, forming a flat-panel type detector head with a sensitive area large enough to cover the whole body of a typical laboratory mouse. Two such detector heads were constructed and their performance was characterized. For one detector head, the energy resolution ranged from 16.1% to 38.5% full width at half maximum (FWHM), with a mean of 20.1%; for the other detector head, the energy resolution ranged from 15.5% to 42.7% FWHM, with a mean of 19.6%. The intrinsic spatial resolution was measured to range from 1.55 mm to 2.39 mm FWHM along the detector short axis and from 1.48 mm to 2.33 mm FWHM along the detector long axis, with an average of 1.78 mm. Coincidence timing resolution for the detector pair was measured to be 4.1 ns FWHM. These measurement results show that the detectors are suitable for our specific application.

A Small-Animal PET System Based on LYSO Crystal Arrays, PS-PMTs and a PCI DAQ Board

A positron emission tomography system for small animals has been designed for research purposes, and developed at Instituto de Fi?sica, UNAM, Mexico. Its detection modules are based on pixelated scintillator LYSO crystal arrays coupled to Hamamatsu H8500 position-sensitive photomultiplier tubes. The front-end electronics are based on nuclear instrumentation modules (NIM) and in-house built readout circuits. Peak signal digitization is performed with a commercial analogue-to-digital acquisition (DAQ) board. The system has been characterized for spatial, timing and energy resolution, system dead time, absolute sensitivity, scatter fraction and noise equivalent count rate (NEC). The results indicate that the detection modules are able to identify individual crystals (out of 400) with up to 8-to-1 peak-to-valley ratios with individual crystal energy resolution ranging from 7 to 15% at 511 keV. The timing resolution is 1.9 ns and the system dead time was found to be 16.8 ?s and 42.1 ?s for 0.5 ml and 10 ml volume sources, respectively. The measured absolute system sensitivity is 0.11% and the scatter fraction from a glass capillary inside a 2.5 cm diameter mouse phantom is 21.5%. A true NEC maximum value was not achieved with the system due to saturation of the PS-PMT output signals for activities above 0.27 mCi. Results from a Na18 F PET bone scan of a 30 g mouse are shown.

Initial characterization of a benchtop microPET system based on LYSO crystal arrays and Hamamatsu H8500 PS-PMTs

A microPET system for small animal studies is currently being developed at Instituto de Física, UNAM. The main goal of this project is to build a cost-effective benchtop system that could be suitable for research purposes. The basic design uses off-the-shelf components and is being assembled using nuclear instrumentation modules and in-house built readout circuits. The detection modules are based on pixelated scintillator LYSO crystal arrays coupled to Hamamatsu H8500 position-sensitive photomultiplier tubes with a resistive chain readout system. Pulse digitization is performed with a commercial fast analogue-to-digital data acquisition board. The uniformity, cross-talk and aperture function of the photomultipliers have been measured. The modules are able to identify individual crystals (out of 400) with a 4-to-1 peak-to-valley ratio. The measured energy resolution of 22Na spectra in individual crystals ranges from 7% to 15%; the dead time of the system is between 17 and 42 μs depending on the source volume, and the resolving time is 1.16±0.01 ns. The design and characterization of the system includes Monte Carlo simulations of the detectors.

Energy calibration of individual crystals in a LYSO pixelated array for microPET detection modules using Voronoi diagrams

Most small-animal positron emission tomography imaging systems nowadays use scintillator crystal arrays coupled to position-sensitive photomultiplier tubes (PS-PMT) as their detector modules. Individual crystal region identification to set tight energy thresholds has been introduced to reduce scatter and pileup events. In this work, we have used Voronoi diagrams to implement both tasks in a fast and efficient way for data analysis from a 20×20 LYSO crystal array coupled to Hamamatsu H8500 PS-PMT. This module forms part of a benchtop microPET system currently being developed at UNAM, Mexico. The results show that the use of individual crystal energy windows does not reduce image distortions, caused by pulse pileup, in 2-D data acquisition projections obtained with our system.

Performance Evaluation of a Dedicated Camera Suitable for Dynamic Radiopharmaceuticals Evaluation in Small Animals

As the result of a collaboration between the Detector and Imaging Group of Thomas Jefferson National Accelerator Facility (US), the Institute of Radioisotopes and Radiodiagnostic Products (IRRP) of N.C.S.R. ldquoDemokritosrdquo and the Biomedical Simulations and Imaging Applications Laboratory (BIOSIM) of National Technical University of Athens (Greece), a mouse sized camera optimized for Tc99m imaging was developed. The detector was built in Jefferson Lab and transferred to Greece, where it was evaluated with phantoms and small animals. The system will be used initially for planar dynamic studies in small animals, in order to assess the performance of new radiolabeled biomolecules for oncological studies. The active area of the detector is approximately 48 mm times 96 mm. It is based on two flat-panel Hamamatsu H8500 position sensitive photomultiplier tubes (PSPMT), a pixelated NaI(Tl) scintillator and a high resolution lead parallel-hole collimator. The system was developed to optimize both sensitivity and resolution for in vivo imaging of small animals injected with technetium compounds. The results of system evaluation in planar mode with phantoms are reported. Results are presented for in vivo dynamic studies of mice injected with > 100 muCi of two conventional and novel radiopharmaceuticals, namely Tc99m-MDP and Tc99m -Bombesin.

Performance evaluation of a mouse-sized camera for dynamic studies in small animals

A mouse sized camera has been built in terms of collaboration between the presenting institutions. The system is used for the performance of dynamic studies in small animals, in order to evaluate novel radiopharmaceuticals. The active area of the detector is approximately 48×96 mm allowing depiction of the entire mouse in a single view. The system is based on two flat-panel Hamamatsu H8500 position sensitive photomultiplier tubes (PSPMT), a pixellated NaI(Tl) scintillator and a copper–beryllium (CuBe) parallel-hole collimator. In this work, the evaluation results of the system are presented, using phantoms and small animals injected with conventional radiophrmaceuticals. Average resolution was ∼1.6 mm on the collimator surface and increased to ∼4.1 mm in 12 cm distance from the detector. The average energy resolution was measured and found to be ∼15.6% for Tc 99m. Results from imaging thin capillaries demonstrated system's high resolution and sensitivity in activity variations was shown. Initial dynamic studies have been carried out in small animals injected with Tc 99m-DTPA and Tc 99m-MDP. The results show system's ability to perform kinetic imaging in small animals.

A compact gamma camera for biological imaging

A compact detector, sized particularly for imaging a mouse, is described. The active area of the detector is approximately 46 mm /spl times/ 96 mm. Two flat-panel Hamamatsu H8500 position-sensitive photomultiplier tubes (PSPMTs) are coupled to a pixellated NaI(Tl) scintillator which views the animal through a copper-beryllium (CuBe) parallel-hole collimator specially designed for /sup 125/I. Although the PSPMTs have insensitive areas at their edges and there is a physical gap, corrections for scintillation light collection at the junction between the two tubes results in a uniform response across the entire rectangular area of the detector. The system described has been developed to optimize both sensitivity and resolution for in-vivo imaging of small animals injected with iodinated compounds. We demonstrate an in-vivo application of this detector, particularly to SPECT, by imaging mice injected with approximately 10-15 /spl mu/Ci of /sup 125/I.