Flat Panel Position Sensitive Photomultiplier Research Articles

Cerium Bromide Single-Crystal X-Ray Detection and Spectral Compatibility Assessment with Various Optical Sensors

Scintillators with high light yield (LY) values are of interest for medical imaging applications, in harsh environments, nondestructive testing (NDT), etc. CeBr3 has a LY of 60000 photons per MeV, a value much higher than other efficient materials, such as Lu3Al5O12:Ce (25000 photons/MeV); thus, its X-ray detection properties would be of interest to be examined for medical imaging applications. The X-ray detection and absorption properties of a single crystal CeBr3 sample along with the compatibility of its produced light with various optoelectronic sensors were examined. In this study, the quantum detection (QDE) and the energy absorption efficiency (EAE) of CeBr3 were calculated. The findings were compared with data for 10 × 10 × 10 m m 3 Lu3Al5O12:Ce and CaF2:Eu single crystals. The measured optical spectrum produced by CeBr3 was well correlated with the spectral response of commercial optical sensors, yielding spectral matching higher than 93% for various photocathodes, e.g., GaAs (94%), E-S20 (95%), and bialkali and multialkali (95-97%), as well as with flat panel position-sensitive photomultipliers (95-99%). The energy absorption properties of CeBr3 were found higher than those of Lu3Al5O12:Ce and CaF2:Eu for X-ray tube voltages greater than 100 kVp. The quantum detection efficiency was 100% across the examined energy range. Even though CeBr3 is hygroscopic and has a mediocre 5.1 g/cm3 density, the QDE, EAE, and spectral correlation results are promising for medical imaging applications.

Quantification of radiotracer uptake with a dedicated breast PET imaging system

Tomographic breast imaging techniques can be used to quantify radiotracer uptake in breast and tumor tissue. However, physical processes common to PET imaging can confound accurate quantification. In this investigation, we assessed the effects of these phenomena and tested correction schemes for our new positron emission mammography-tomography system (PEM-PET). The PEM-PET scanner utilizes two sets of rotating planar detector heads. Each unit consists of a 4 x 3 array of Hamamatsu H8500 flat panel position sensitive photomultipliers coupled to a 96 x 72 array of 2 x 2 x 15 mm3 LYSO detector elements (pitch = 2.1 mm). Image reconstruction is performed with a 3D-OSEM algorithm parallelized to run on a multiprocessor computer system. The reconstructed field-of-view is 15 x 15 x 15 cm3. Much of the testing procedures were based on NEMA-NU2/2001 protocols. Count rate losses due to pulse pile-up, image contamination due to acceptance of random coincidences and Compton scatter, and image artifacts produced by photon attenuation were measured. It was found that the system was susceptible to count rate losses when moderate levels of radiation were present in the scanner due to the current design of the event trigger electronics. Application of corrections for Compton scattering, photon attenuation and dead time resulted in improved estimations of 18F concentration in simplified phantom studies. Results from these preliminary studies indicate that the PEM-PET scanner will be useful for the quantification of radiotracer uptake in breast tumors, possibly facilitating early assessment of cancer treatments.

The positron emission mammography/tomography breast imaging and biopsy system (PEM/PET): design, construction and phantom-based measurements

Tomographic breast imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. We have developed a high-resolution positron emission mammography/tomography imaging and biopsy device (called PEM/PET) to detect and guide the biopsy of suspicious breast lesions. PET images are acquired to detect suspicious focal uptake of the radiotracer and guide biopsy of the area. Limited-angle PEM images could then be used to verify the biopsy needle position prior to tissue sampling. The PEM/PET scanner consists of two sets of rotating planar detector heads. Each detector consists of a 4 × 3 array of Hamamatsu H8500 flat panel position sensitive photomultipliers (PSPMTs) coupled to a 96 × 72 array of 2 × 2 × 15 mm3 LYSO detector elements (pitch = 2.1 mm). Image reconstruction is performed with a three-dimensional, ordered set expectation maximization (OSEM) algorithm parallelized to run on a multi-processor computer system. The reconstructed field of view (FOV) is 15 × 15 × 15 cm3. Initial phantom-based testing of the device is focusing upon its PET imaging capabilities. Specifically, spatial resolution and detection sensitivity were assessed. The results from these measurements yielded a spatial resolution at the center of the FOV of 2.01 ± 0.09 mm (radial), 2.04 ± 0.08 mm (tangential) and 1.84 ± 0.07 mm (axial). At a radius of 7 cm from the center of the scanner, the results were 2.11 ± 0.08 mm (radial), 2.16 ± 0.07 mm (tangential) and 1.87 ± 0.08 mm (axial). Maximum system detection sensitivity of the scanner is 488.9 kcps µCi−1 ml−1 (6.88%). These promising findings indicate that PEM/PET may be an effective system for the detection and diagnosis of breast cancer.For more information on this article, see medicalphysicsweb.org

Performance Results of BGO Block Detectors Based on Flat Panel PS-PMT for PET

We have developed a new detector composed of a 20times20 array of 2times2times20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (BGO) scintillators and a novel flat panel position sensitive photomultiplier tube(FP-PS-PMT) - Hamamatsu R8400-00-M256. The performance of the block detector was evaluated in terms of applicability to positron emission tomography (PET). The energy resolution was about 23% FWHM for 511 keV gamma-rays. The spatial resolution of the detector was evaluated by measuring the detector response functions (DRFs) for each BGO segment and by measuring the coincidence response functions (CRFs). The average FWHM values of the DRFs were 2.0 mm. For the CRFs performance, the average FWHM values were 2.82 mm at 0deg and 5.20 mm at 30deg.

8-Layer DOI Encoding of 3-Dimensional Crystal Array

An 8-layer depth of interaction (DOI) detector was designed based on the technique we have developed for 4-layer DOI detectors. The new detector achieves 8-layer DOI encoding by pulse shape discrimination (2-layer DOI encoding) and an optimized reflector arrangement in a 3-dimensional crystal array (4-layer DOI encoding). Its capability was proved with an 8-layer 10times10 Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (GSO) crystal array coupled to a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). The dimensions of each crystal element were 2.90 mmtimes2.90 mmtimes3.75 mm and the interval between 16times16 multi anodes in the 256ch FP-PMT was 3.04 mm. Two different dopant concentrations in GSO were chosen for pulse shape discrimination: GSO crystals of 0.5 mol% and 1.5 mol% Ce dopant that have 60 ns and 35 ns scintillation decay times, respectively. In the crystal array, Layer-1, the farthest from the 256ch FP-PMT, and Layers-3, -5 and -7 were composed of GSO crystals of 0.5 mol% Ce dopant. All other layers were composed of GSO crystals of 1.5 mol% Ce dopant. Performance of the 8-layer DOI detector was evaluated by irradiating with 662 keV uniform gamma-rays and the capability was judged to be good. To prove the validity of the layer encoding, a fan-beam of 662 keV gamma-rays was irradiated onto the side face of each layer. The obtained 2-dimensional position histograms showed the right structure in each corresponding layer clearly. Light output uniformity among DOI layers and energy resolutions were measured on the pulse height distributions of the central crystal in each layer. The crystals in Layer-2 and Layer-3 showed the smallest light output and their full energy peak channels were 62% to the largest peak channel of the Layer-8 crystal distribution. Energy resolutions were about 15% for all eight layers

Optimization of a mini-gamma camera based on a 2×2 array of Hamamatsu H8500 PSPMTs

We present the results of a comparative study between several scintillation sensors with the goal of optimizing the spatial resolution of a practical mini-gamma camera based on a 2×2 array of Hamamatsu H8500 flat panel position sensitive photomultiplier tubes (PSPMTs) with 64 anode pads per PSPMT. The readout of this 256 pad imager was achieved by a special in-house designed and optimized pad-decoupling strip readout reducing the number of readout channels to 32. Pixellated NaI(Tl) and CsI(Tl) scintillator arrays, as well as thin continuous GSO, GSOZ, CsI(Na) and CsI(Tl) scintillator plates were coupled to this PSPMT array to form a compact mini-gamma camera. This round of tests, following extensive prior experience with this type of imager, was intended to investigate the possibility of achieving an intrinsic spatial resolution of under 1.0 mm FWHM across the whole surface of the mini-gamma camera. We confirmed the results of our previous studies that the best overall performance is achieved with pixellated NaI(Tl) arrays. The present resolution limit attainable with the H8500 PSPMT array is approaching 1.2 mm FWHM, which is equivalent to the smallest available pixel pitch of these arrays.

Comparison of different approaches based on Monte Carlo methods to calculate the system matrix for small animal PET

This study focuses on Monte Carlo (MC) based techniques to calculate the system matrix (SM) for iterative image reconstruction of small animal PET data. For most PET scanners, the calculation of the SM requires extremely long simulation times due to the large number of image voxels, even when considering symmetries. Our goal is to determine in advance which simplifications can be done to accelerate the MC simulation without jeopardizing the accuracy of the SM. Our small animal scanner prototype was simulated using GATE. It consists of a continuous LSO crystal (42×42×10 mm 3) attached to Flat Panel position sensitive photomultipliers. We investigated three different radioactivity distribution models to compute the SM elements for five representative voxel positions. The results show that the simulation time required to compute the whole SM and the accuracy of the SM depend on the model and on the voxel position. In the inner region of the field of view (FOV), the model with eight point sources distributed within each voxel yields the best trade-off between simulation time and SM accuracy. Whereas, for the peripheral region of the FOV, the model with one emission point at the center of the voxel yields the best compromise. The analysis was carried out with and without having depth-of-interaction (DOI) into account. The effect of the distribution model is more significant when DOI is considered.

Preliminary evaluation of four-layer BGO DOI-detector for PET

We found that Bi/sub 4/Ge/sub 3/ O/sub 12/ (BGO) scintillator can be elements of a four-layer depth of interaction (DOI) detector and it was proved with a 12/spl times/12/spl times/4 array of BGO crystals in dimensions of 2.9 mm/spl times/2.9 mm/spl times/7.5 mm coupled to a 256-channel flat panel position sensitive photomultiplier tube. Appropriate reflector insertion in the array makes all crystal identification possible on one position histogram. Despite the large refractivity and small light output of BGO, the four-layer BGO detector showed no significant variation in the full energy peaks among all crystal elements. When no optical grease was used in the construction of the BGO DOI-block and irradiated with gamma-rays from /sup 137/Cs, a top layer crystal has 80% of light output relative to the bottom layer. The obtained two-dimensional position histogram by the irradiation was clear enough to allow identification of the crystals of interaction. Profiles of the histogram show peak-to-valley ratio of 1.9:1 for the top layer crystals and larger ratio for other layer crystals in the experiment.

Performance evaluation of a subset of a four-layer LSO detector for a small animal DOI PET scanner: jPET-RD

Previously, we proposed a new depth of interaction (DOI) encoding method and proved that it worked successfully with four-layered Gd/sub 2/SiO/sub 5/ crystals for a small animal positron emission tomography (PET) detector. We are now planning to develop a small animal PET scanner, jPET-RD (for rodents with DOI detectors), which has both high resolution and high sensitivity by the use of a DOI detector with a 32/spl times/32/spl times/4 crystal array. The scintillator for the detector will be Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO). In this work, we evaluated performance of a DOI detector composed of four layers of a 12/spl times/12 LYSO (Lu: 98%, Y: 2%) crystal array by irradiating 511 keV gamma rays uniformly. The new encoding method was used for crystal identification. The size of each crystal was 1.46 mm/spl times/1.46 mm/spl times/4.5 mm. The crystal block was coupled to a 256-channel flat panel position sensitive photomultiplier tube, which has 16/spl times/16 multi anodes at intervals of 3.04 mm. As we expected, all crystals are expressed on a single two-dimensional position histogram without overlapping. Energy resolution of all events is 21.8% and time resolution of all events is 0.69 ns in FWHM. When layers are counted from the top, the energy resolutions of the first, second, third, and fourth layer events are 11.6%, 12.3%, 13.3%, and 19.1% and the time resolutions are 0.60ns, 0.59ns, 0.60ns, and 0.66ns, respectively.

Performance of 256ch flat panel PS-PMT with small crystals for a DOI PET detector

A 256 channel flat panel position sensitive photomultiplier tube (256ch FP-PMT) was evaluated for application to a depth of interaction (DOI) PET detector composed of small crystal elements. The 256ch FP-PMT has 52 /spl times/ 52 mm opening area with 89% useful area. Its 256 anodes are placed at a 3.04 mm interval. To estimate the FP-PMT performance, light spread functions of anodes at central and peripheral regions of a prototype 256ch FP-PMT were measured with a Gd/sub 2/SiO/sub 5/ (GSO) crystal sized 1.42 /spl times/ 1.42 /spl times/ 4.5 mm. The crystal cross section area is about one quarter of one anode area of the FP-PMT. It was found that light spread functions of peripheral anodes were similar to the functions of central anodes and also the functions measured with a 2.9 /spl times/ 2.9 /spl times/ 7.5 mm GSO crystal which has almost the same dimensions of cross-section as the anode area. Transit time fluctuation among the 256ch FP-PMT anodes was estimated by measuring time resolutions of a LuYSiO/sub 5/ (LYSO) crystal at some central and peripheral positions. The LYSO crystal has the same dimensions as the smaller GSO crystal. BaF/sub 2/ was used for a reference detector. The obtained distributions show about the same time resolution between the central and peripheral positions and the full width at half maximum is (366 /spl plusmn/ 15) ps. The transit time fluctuation is /spl plusmn/ 106 ps. Two-dimensional position histograms of a 32 /spl times/ 32 GSO crystal array and two layers of 9 /spl times/ 9 GSO crystal arrays are obtained by uniform gamma-ray irradiation. The crystal dimensions are 1.42 /spl times/ 1.42 /spl times/ 4.5 mm so that the 32 /spl times/ 32 array covers all the useful area and indicates variation of crystal identification performance over the useful area. The 9 /spl times/ 9 /spl times/ 2 array is coupled to peripheral region. The resultant histograms confirm that a 256ch FP-PMT has enough capability for identifying crystals of this size even on the periphery and in DOI arrangement.

Three-dimensional array of scintillation crystals with proper reflector arrangement for a depth of interaction detector

A new method to acquire four-layer depth of interaction (DOI) information is proposed for the next generation positron emission tomography scanner (jPET-D4) that realizes high resolution and high sensitivity. The detector module of the jPET-D4 is a 16/spl times/16/spl times/4 Gd/sub 2/SiO/sub 5/: Ce (GSO) multicrystal array coupled with a 256 ch flat panel position sensitive photomultiplier tube (256 ch FP-PMT) having large opening area. The first challenge to encode DOI information was carried out with 8/spl times/8 array of units consisted of 2/spl times/2/spl times/4 crystal elements. The unit is developed for four-layer DOI encoding in previous report. Its crystal identification performance is evaluated by uniform gamma ray irradiation. The measured scintillation events are mapped on a two-dimensional (2-D) position histogram according to the relative ratio of the multianode output of the FP-PMT. However, peaks corresponding to the crystal elements of one unit form a colony in the resultant 2-D position histogram and there is large space between adjacent colonies. In the new method, the reflector arrangement which makes proper light sharing in the multicrystal array decreases such wasted space. Consequently, peak-to-valley on the 2-D position histogram was improved to 3.3:1 from 1.8:1. We found energy performance was also enhanced by the new method.

A four-Layer depth of interaction detector block for small animal PET

We are now planning to develop a positron emission tomograph dedicated to small animals, such as rats and mice, which meets the demand for higher sensitivity. For the positron emission tomography (PET), we newly designed a four-layer depth of interaction (DOI) detector, which is constructed of all the same crystal elements. In this DOI detector, appropriate insertion of the reflector controls the behavior of scintillation photons by inserting the reflectors between crystal elements so that the DOI information of four layers can be extracted from one two-dimensional (2-D) position histogram made by Anger-type calculation. As a preliminary experiment, we measured crystal identification performance of the DOI detector, which consists of four layers of a 16 /spl times/ 16 crystal array using Gd/sub 2/SiO/sub 5/ crystals with Ce concentration of 0.5 mol %. Each crystal is in dimensions of 1.42 mm /spl times/ 1.42 mm /spl times/ 4.5 mm. A crystal block is optically coupled to a 256-channel flat panel position sensitive photomultiplier tube whose opening area is 52.0 mm /spl times/ 52.0 mm. We obtained sufficient positioning performance for this four-layer DOI detector on the 2-D position histogram. We concluded that it would be a promising device to realize a small animal PET scanner with high sensitivity and high resolution.

Performance of a PET Detector With a 256ch Flat Panel PS-PMT

A 256ch flat panel position sensitive photomultiplier tube (FP-PMT) is a promising device for a PET detector because of its large opening area, 52 mm /spl times/ 52 mm, and small dead space. The useful area of the 256ch FP-PMT is 89% to the opening area. The 256ch FP-PMT contains 16 /spl times/ 16 matrix anodes with 3.04 mm intervals between them so that the 256ch FP-PMT affords optical coupling with a 16 /spl times/ 16 array of scintillation crystals having 3 mm /spl times/ 3 mm bottom area. Its 14.7 mm thickness will also ensure a compact volume and less weight for the PET apparatus. Using a prototype 256ch FP-PMT, we measured light spread function of a central anode and crystal identification ability with 2.9 mm /spl times/ 2.9 mm /spl times/ 7.5 mm Gd/sub 2/SiO/sub 5/ (GSO) crystals. The full width at half maximum of the light spread function was found to be 4.6 mm. As regards positioning performance, the resultant positioning image map assures its capability for crystal identification in a 16 /spl times/ 16 array of the GSO crystals. For the use of a 256ch FP-PMT having a large useful area, we made a new proposal for easier construction of an array with many crystal elements. The way utilizing multilayer polymer mirrors, a reflector, properly processed by laser can be applied to other various shaped detectors.

Flat Panel PMT for photon emission imaging

Over the last 15 years Hamamatsu has been developed two generations of Position Sensitive Photomultipliers (PSPMTs). The first and the second generation were based on mesh dynode and metal channel dynode respectively. In this paper, we present the first results obtained from the last generation: Hamamatsu H8500 Flat Panel PSPMT. The active area is increased to 2in. with minimum peripheral dead zone and thickness down to 12.5mm. Measurements were addressed to nuclear medicine for single photon imaging. To this aim, we have taken into account two different electronic readout: resistive chain and multi-anode readout (64 channels). To evaluate the imaging performance, the Flat Panel PSPMT was coupled to CsI(Tl) and NaI(Tl) scintillation arrays with pixel size of 3 and 2mm, respectively. Images of CsI(Tl) array, obtained by multi-anode readout, showed an improvement of spatial resolution, from 1.2 to 0.8mm, and of position linearity response. On the contrary for NaI(Tl) array, no relevant image differences between two system readout were obtained.