Sensitive Photomultiplier Tube Research Articles

Development of a phoswich imaging detector to simultaneously acquire neutron and gamma photon images

A neutron detector requires selectively detecting neutrons not detecting gamma photons. However, since gamma photons are commonly emitted from a neutron source, the separation of neutrons and gamma photons is sometimes difficult. To solve this problem, we developed a phoswich imaging detector that can simultaneously but independently acquire images of neutrons and gamma photons. The developed neutron imaging system consists of a lithium-containing silver doped zinc sulfide (Li–ZnS(Ag)) plate stacked on a cerium doped yttrium aluminum perovskite (YAP(Ce)) plate to form a phoswich detector, which is optically coupled to a position sensitive photomultiplier tube (PSPMT). Neutrons are detected by the Li–ZnS(Ag) plate while gamma photons are detected by the YAP(Ce) plate. The scintillation light from the Li–ZnS(Ag) and YAP(Ce) plates is detected by the PSPMT, and the position of interaction is calculated. Pulse shape discrimination is used to separate the images of neutrons and gamma photons. The spatial resolution of the imaging detector for neutrons is ∼2.6 mm FWHM, and the sensitivity for 252Cf neutrons at 2 cm from the source enclosed in 2-cm-thick polystyrene plates is 5.2 cps/MBq. The spatial resolution of the imaging detector for gamma photons is also ∼2.6 mm FWHM, and the sensitivity for 60Co gamma photons at 2 cm from the source within 2-cm-thick polystyrene plates is 375 cps/MBq. The contamination by gamma photons in the neutron window was negligible. The developed phoswich imaging detector can simultaneously and independently acquire the images of neutrons and gamma photons, and thus it will impact the relevant research and applications of neutron detectors and imaging.

Development of a GAGG(Ce)-based compact 3D scanning setup for assessment of active volume in [formula omitted]-ray detectors

A Ce-doped GAGG (Gadolinium Aluminum Gallium Garnet: Gd3Al2Ga3O12) scintillator crystal has been coupled with a multianode position sensitive photomultiplier tube (PSPMT). The system is made compact by employing an external resistive network that reduces the 64 readouts of the PSPMT to only four signals. The resulting GAGG(Ce)-PSPMT setup has been put to use for quick scanning of γ-ray detectors by reconstructing the image of the latter with coincident photons between the pair of detectors. In the present work, such scans are demonstrated for an old single-crystal coaxial reverse-electrode HPGe detector as well as an old clover HPGe detector. For the single-crystal HPGe, the growth of the effective depleted region under increasing reverse-bias voltages has been visualized from the image reconstruction. The active volume is seen to grow from the surface towards the axial cavity. For the clover HPGe detector, dysfunctional portions in the crystals could be identified. The experimental results are found to agree well with simulation carried out using the GEANT4 toolkit. Scanning a detector using this method is faster compared to the scanning process by a point source.

R &D of wavelength-shifting reflectors and characterization of the quantum efficiency of tetraphenyl butadiene and polyethylene naphthalate in liquid argon

Detectors based on liquid argon (LAr) often require surfaces that can shift vacuum ultraviolet (VUV) light and reflect the visible shifted light. For the LAr instrumentation of the LEGEND-200 neutrinoless double beta decay experiment, several square meters of wavelength-shifting reflectors (WLSR) were prepared: the reflector Tetratex® (TTX) was in-situ evaporated with the wavelength shifter tetraphenyl butadiene (TPB). For even larger detectors, TPB evaporation will be more challenging and plastic films of polyethylene naphthalate (PEN) are considered as an option to ease scalability. In this work, we first characterized the absorption (and reflectivity) of PEN, TPB (and TTX) films in response to visible light. We then measured TPB and PEN coupled to TTX in a LAr setup equipped with a VUV sensitive photomultiplier tube. The effective VUV photon yield in the setup was first measured using an absorbing reference sample, and the VUV reflectivity of TTX quantified. The characterization and simulation of the setup along with the measurements and modelling of the optical parameters of TPB, PEN and TTX allowed to estimate the absolute quantum efficiency (QE) of TPB and PEN in LAr (at 87K) for the first time: these were found to be above 67 and 49%, respectively (at 90% CL). These results provide relevant input for the optical simulations of experiments that use TPB in LAr, such as LEGEND-200, and for experiments that plan to use TPB or PEN to shift VUV scintillation light.

First report on the persist time of the free radical produced by shock wave pulses employed in clinical ESWL

The shock wave used in extracorporeal shock wave lithotripsy (ESWL) induces strong cavitation and generates a large amount of free radicals (FR). In order to evaluate the harmfulness of FR in the ESWL, information on the incidence and persist time of FR caused by shock waves is required. FR markers can estimate the amount of FR generated, but not how long the FRs will survive. The OH* FR generated by the ESWL shock wave reacts with luminol and emits blue light, which is called sonochemical luminescence (SCL) phenomenon. In this study, FR generation and persist time were measured by recording SCL phenomenon with a sensitive photomultiplier tube (PMT) that responds in nanoseconds. As a result of measurement with the PMT, when the electromagnetic shock wave used in clinical practice was irradiated to the luminol solution, the amount of light emitted per unit time reached its maximum value within a very short time (< ∼600us) and then exponentially decreased for a long time (∼several hundred ms). The measured FR persist time reaches a maximum of 1000 ms. As the output setting of the shock wave generator increases, the minimum or average FR persist time increases, but the maximum value does not show a high correlation with the output setting. The amount of generated FR shows a very high correlation with the shock wave setting, and when the setting is changed from low to high, it increases very sensitively, rapidly and non-linearly. In order to reduce the risk of FR in patient treatment using lithotripsy, the output setting of the shock wave should be minimized, and the interval between the shock wave pulses should be sufficiently larger than the FR persist time. Therefore, it is recommended to avoid increasing the output setting and setting the shock wave irradiation frequency below 1 Hz to shorten the treatment time in clinical practice. For the purpose of formulating these recommendations, additional studies on the generation and persist time of FR depending on the shock wave generation method and set conditions in living tissue or similar environment are required in the future.

Characterization and Pilot Human Trial of Dedicated Breast Ring Positron Emission Tomography (BRPET) System

We describe the design and performance of BRPET, a novel dedicated breast PET (dbPET) scanner designed to maximize visualization of posterior regions of the breast. BRPET uses prone imaging geometry and a 12-module detector ring built from pixelated LYSO crystals coupled to position sensitive photomultiplier tubes (PSPMTs). Optical coupling via slanted plastic fiber optic light guides permits partial insertion of the crystals into the exam table’s breast aperture. Image quality testing procedures were adapted from the NEMA NU4-2008 protocol. Two additional phantom tests quantified the posterior extent of the usable volume of view (VoV). BRPET axial, radial, and tangential FWHM spatial resolutions at the isocenter were 1.8, 1.7, and 1.9 mm, respectively. The peak absolute system sensitivity was 0.97% using an energy window of 460–562 keV. The peak noise equivalent counting rate was 5.33 kcps at 21.6 MBq. The scanner VoV extends to within ~6 mm of the plane defining the location of the chest wall. A pilot human study (n = 10) compared the diagnostic performance of FDG-BRPET to that of contrast enhanced MRI (CEMRI), with biopsy as ground truth. Averaged over three expert human observers, the sensitivity/specificity for BRPET was 0.93/1.0, compared to 1.0/0.25 for CEMRI.

Development of GGAG alpha camera system for targeted alpha radionuclide therapy research

Cerium doped Gd3(GaAl)5O12 (GGAG) scintillator has a character in which the decay time for alpha particles differs from that of gamma photons. This is a good point for an imaging detector used for alpha autoradiography of a mouse administered Astatine-211 (At-211) in radionuclide therapy research. Thus, we developed an alpha camera system using a GGAG imaging detector combined with a charge-coupled device (CCD) camera. Our GGAG imaging detector is made of a 0.5 mm-thick GGAG plate optically coupled to a position sensitive photomultiplier tube (PSPMT) and set in a stand with the CCD camera positioned on the upper side of the imaging detector to take optical photos. We first measured the performance of our alpha camera system using an Am-241 alpha source and natural alpha emitting radionuclides with radon daughters. We then conducted imaging of the non-sliced organs of a mouse. After the imaging detector surface was covered with 2.5 µm-thick Mylar film, the organs of the At-211-administered mouse was set on the imaging detector after split or opened and the alpha emitter distributions were measured. We used pulse shape analysis to separate the alpha particles from the beta particles or gamma photons. We successfully measured the alpha particle distributions of the wet non-sliced organs of the At-211-administered mouse. Using the pulse shape spectrum, we could separate the alpha particle images and beta particle or gamma photon images. We conclude that the developed alpha camera system is promising for the imaging of alpha particles and separating of the images using pulse shape discrimination.

Using a Low-Cost Green Light Emitting Diode to Measure Total Suspended Solids in a Marine Protected Area of the Philippines

Fernandez, P.N.J., 2022. Using a low-cost green light emitting diode to measure total suspended solids in a marine protected area of the Philippines. Journal of Coastal Research, 38(1), 99–113. Coconut Creek (Florida), ISSN 0749-0208. Seawater parameters are important indicators of coastal water conditions. One of the essential parameters is the total suspended solids (TSS). This study probed how to use a low-cost 535-nm green LED to measure the TSS in marine protected areas of barangay Lo-ong, Concepcion, Iloilo, Philippines. It aims to examine the relationship of the total attenuation coefficients (TAC) to total suspended solids (TSS) values in coastal water. Sample sea waters were taken from various locations and brought to a laboratory for a filtration process known as gravimetry. Different available filter paper sizes (1.5 microns, 6 microns, 20 microns, and 50 microns) were used in the filtration process and were dried in a controlled constant temperature of 110 degrees Celsius for 24 hours using an electric oven. Dried filter papers' weights were measured using an analytical balance before using the infiltration of seawater. TAC values were also measured in different seawater samples using a prototype device made up of LED and photodiode. This study demonstrated that TAC values of green LEDs are positively correlated with TSS values (R value of 0.45). Results reveal that the moderate correlation between an LED's TAC values to TSS positively proved that a low-cost LED can be used as an alternative to the more expensive remote sensing satellite data. Findings of the study also showed that TSS values in the marine protected area under study were far below the acceptable limits for coastal waters. The performance of the LED-based measuring device can still be improved in the future by using collimating lenses and more sensitive photomultiplier tubes.

Optical fiber-based ZnS(Ag) detector for selectively detecting alpha particles

In alpha radionuclide therapy, an optical fiber-based alpha particle detector is a new tool that could possibly be employed for the direct detection of alpha particles in subjects. Thus, in the present study, we developed an optical fiber-based alpha particle detector. The alpha particle detector was made of a 1mm diameter, 10 cm long plastic double clad optical fiber drilled a 0.7 mm diameter, 2 mm depth open space at the one end of the fiber. Silver-doped zinc sulfide (ZnS (Ag)) was painted inside this open space to form a ZnS(Ag) small scintillation chamber. To conduct performance comparisons, we also developed a fiber detector using the same fiber in which a Ce-doped Lu1.8Y0·2SiO5 (LYSO(Ce)) scintillator with dimensions of 0.32 mm × 0.5 mm × 5 mm was inserted. Both fiber detectors were wrapped in aluminized Mylar and optically coupled to a position sensitive photomultiplier tube, before calculating the two-dimensional distributions, energy, and pulse shape spectra. For 5.5-MeV alpha particles, the ZnS(Ag) fiber detector produced ~ 5 times larger pulse heights and the count rate was ~2 times higher compared with those using the LYSO(Ce) fiber detector. For the maximum energy 2.28-MeV beta particles and 0.66-MeV gamma photons, the ZnS(Ag) fiber detector produced no counts, but it yielded small counts from natural alpha particles. Our results confirmed that the ZnS(Ag) fiber detector developed in this study could selectively detect alpha particles and it was insensitive to beta particles and gamma photons.

Sensitivity improvement of YAP(Ce) cameras for imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation: problem and solution

Low-energy x-ray imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation is a promising method for range estimation and could be used for imaging with almost clinical dose levels of carbon ion. However, the number of counts in images with clinical dose levels is relatively small, making it difficult to obtain precise range estimations. Since improving the sensitivity of the x-ray camera may solve this issue, we developed two new types of x-ray cameras. One uses a 1 mm thick, 40 mm × 40 mm cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) scintillator plate combined with a 2 inch square flat panel photomultiplier tube (FP-PMT) contained in a 2 cm thick tungsten shield with a pinhole collimator positioned 50 mm from the scintillator; the other uses a 0.5 mm thick, 20 mm × 20 mm YAP(Ce) scintillator plate combined with a 1 inch square position sensitive photomultiplier tube (PSPMT) contained in the same tungsten shield with a pinhole collimator, but with the scintillator positioned closer (30 mm) to the pinhole collimator to obtain a similar field of view. For both cameras, we used a wider angle (∼55°) pinhole collimator to measure the phantom closer to improve sensitivity. Although the 40 mm × 40 mm YAP(Ce) camera had high system spatial resolution, the background count fractions were high and produced a high count area at the center of the images due to the pulse pileup of the signals. With the 20 mm × 20 mm YAP(Ce) camera, we obtained x-ray images with low background counts without a high count area at the image center. By smoothing the measured images, we were able to estimate the ranges even for clinical dose levels. We therefore confirmed that one of our newly developed YAP(Ce) cameras had high sensitivity and is promising for the imaging of secondary electron bremsstrahlung x-rays during irradiation of carbon ions in clinical conditions.

A Small Field, High Resolution γ-Camera System dedicated to SPECT Imaging

A small field, high resolution γ-Camera system dedicated to radiopharmaceutical research and other clinical SPECT (Single Photon Emission Computed Tomography) applications is currently being developed in our group. The system is equipped with the 3” HAMAMATSU R2486 Position Sensitive PhotoMultiplier Tube (PSPMT) with a 16X+16Y-crossed wire anode and various pixelated and ho- mogeneous scintillation crystals. Planar images are created from the recorded charge signals by applying the resistive chain technique. The main part of this work focuses on the development of new correction methods for the improvement of the spatial resolution and the uniformity of the γ-Camera. The spatial distortion correction technique is based on lookup tables with the coordinates of reference points which are selected during the calibration phase of the system for a given set of collimator and scintillation crystal. The applied algorithm incorporates 2D-interpolation tech- niques and has been developed on a full automated graphics environment making use of the HIGZ (High Level Interface to Graphics and ZEBRA) program libraries from CERN. Both correction methods for the spatial distortion and non-uniformity have been applied to phantom images using several combinations of small capillaries filled with water solution of 99mTc. Comparative studies are shown on planar im- ages for different phantom geometries. The method is also extended to tomographic images and the obtained SPECT improvement in resolution is discussed.

Sensitivity and Resolution Study of a Small-Field γ-Camera System on a Tomographic Level

The sensitivity and the spatial resolution of a small-field γ-Camera system based on a Position Sensitive Photomultiplier Tube (PSPMT) on a tomographic level are examined in this study. A cylindrical Gel-Phantom (d = 40 mm, h = 50 mm) with cylindro-conoidal tubes and capillaries (from 64 to 640 mm3 in volume) containing water solution of 99mTc is used as a test phantom in the present work. A total of 24 projections covering the full angle region (0°-360°) are obtained with the γ-Camera system under examination. The planar information is further analyzed to reconstruct the tomographic images taking into account all off-line corrections needed to remove barreloid deformations appearing at the edges of the Field-of- View. The reconstruction procedure is performed with iterative algorithms and for comparison reasons two different techniques (MLEM and accelerated ART) are used. The variety of the 99mTc-volumes in the phantom with the given specific radioactivity and the phantom axial asymmetry, due to the diÆerent radial distances of the tubes in the gel environment, allow a realistic characterization of the system’s performance on a tomographic level. Obtained experimental results for the system sensitivity and spatial resolution are presented and discussed in this work.

Optical Properties of Continuous and Pixelated Scintillation Crystals

The optical photon distribution produced inside continuous and pixelated scintillation crystals by the absorption of a γ-ray have been studied with the photon transport program DETECT 2000. With this program the charge signals recorded by a multi-wired anode system, like the Position Sensitive PhotoMultiplier Tube (PSPMT) of a γ-Camera, are simulated. Based on the analytical parametrization which is fitted to experimental data, a new position reconstruction method for PSPMTs is proposed in this work. Planar images have been reconstructed with the new method and compared to the traditional charge center of gravity technique. Data are obtained from a small field, high resolution γ-Camera system with a multi- wired crossed anode using the R2486 (HAMAMATSU) PSPMT. Systematic studies for continuous and pixelated inorganic scintillation crystals of CsI(Tl) have been performed for different phantom geometries using small capillaries of 99mTc. The developed method seems to drastically improve the resolution of the reconstructed planar information, even when homogeneous crystals are used.

Position and Energy Resolution of a γ-Camera based on a Position Sensitive Photomultiplier Tube

Studies of the spatial- and energy-resolution of a small field, high resolution γ-Camera system currently being developed in our laboratory are presented here. The system is based on a cylindrical Position Sensitive Photo-Multiplier Tube (HAMAMATSU R2486) with 32 crossed-wired anodes, arranged in two orthogonal groups. The anode outputs are connected to a resistive current divider network and after pre-amplification are guided to a local digitizing system. A PCI-Analog to Digital Converter card with a maximum sampling rate of 20 MHz and the rest of the Data Acquisition System is controlled by software running on the LabVIEW environment. Position and induced charge of the incident light pulses can be easily reconstructed through a variety of offline algorithms. In the first part of this study the intrinsic response of the PMT and especially its energy and position resolution is presented. The experimental procedure utilizes the controlled pulse light output of a LED guided through fiber glass directly to the PMT’s entrance. The accumulated charge distribution and charge spread as a function of the incident number of photons is studied. In the second part, the response of the integrated γ-Camera system after the application of typical scintillation crystals for 99Tc radioactive phantoms is measured and analyzed.

Feasibility evaluation of a direct detection method of alpha particles in water using YGAG plate with pulse shape analysis

Ce doped (YGd)3(GaAl)5O12:Ce (YGAG) is a ceramic scintillator with high light output, and its decay times are different between alpha particles and gamma photons or beta particles. This characteristic may be applied to the direct measurement of alpha particles in water where the gamma photons or beta particles become background counts. Thus we proposed a radiation detector using a YGAG plate dipped in water that contained alpha radionuclides to detect alpha particles in water. The scintillation photons from the YGAG plate were detected by a position sensitive photomultiplier tube (PSPMT) set in water that contained alpha radionuclides. A YGAG plate (20 × 20 × 0.5 mm) was set on the bottom of a glass cup filled with water containing alpha radionuclides that emit alpha particles. The alpha particles near the YGAG plate were detected by the scintillator, and the scintillation light was detected by the PSPMT . For radon-containing water sampled from a hot spring, pulse shape spectra showed two peaks: one for the alpha particles and another for the beta particles and the gamma photons. By pulse shape discrimination for the peak of the alpha particles, their count rate decreased with a decay of Rn-222 (3.8 days). For tap water, the pulse shape distribution showed only one peak and the count rate was almost constant, indicating these counts were mainly from the background beta particles or gamma photons. We could show a detection principle for alpha radionuclides in water and this detection principle for alpha radionuclides in water might be a new method for estimating the alpha radionuclide concentration in water.

Gain Invariant Coordinate Reconstruction for SiPM-Based Pixelated Gamma Detectors With Multiplexed Readout

Currently, the prevailing high-resolution Positron Emission Tomography (PET) detector architecture consists of pixelated scintillating crystals coupled to a photosensitive layer, such as position sensitive photomultiplier tubes (PS-PMTs) or silicon photomultiplier (SiPM) arrays. In such detector designs, a light guide layer is commonly used between the finely segmented scintillating crystal array and coarsely segmented photosensitive layer to disperse scintillation light over several elements of the photosensitive layer. Such detectors typically rely on some form of analog signal multiplexing to minimize the number of readout electronics channels and employ Center-of-Gravity (CoG) approach to calculate the positions of gamma-ray interactions. In this article, we report on the Truncated Center of Gravity (TCoG) and Raised-To-the-Power (RTP) algorithms for calculation of gamma photon scintillation position as applied to our newly developed small-scale prototype PET system consisting of a pair of opposing detectors based on $24\times24$ LYSO scintillation crystal matrices and $8\times 8$ SiPM arrays with 64:16 multiplexed readout. The major notable advantage of using TCoG or RTP algorithm in contrast to basic CoG is shown to be their independence of photosensor gain variations. An improvement in the calculation of scintillation positions is demonstrated both for TCoG and RTP algorithms, the Field of View (FOV) distortion inherent to CoG reconstruction is eliminated. On average, the Peak-to-Valley Ratio (PVR) is increased at least by a factor of 2.25. The energy resolution for the considered small-scale PET prototype is ~13.5% when using CoG, TCoG, or RTP reconstruction algorithms.

Development of a position sensitive CsI(Tl) crystal array

Abstract A position-sensitive CsI(Tl) crystal array coupled with the multi-anode position sensitive photomultiplier tube (PS-PMT), Hamamatsu H8500C, has been developed at the Institute of Modern Physics. An effective, fast, and economical readout circuit based on discretized positioning circuit (DPC) bridge was designed for the 64-channel multi-anode flat panel PSPMT. The horizontal and vertical position resolutions are 0.58 mm and 0.63 mm respectively for the 1.0 × 1.0 × 5.0 mm3 CsI(Tl) array, and the horizontal and vertical position resolutions are 0.86 mm and 0.80 mm respectively for the 2.0 × 2.0 × 10.0 mm3 CsI(Tl) array. These results show that the CsI(Tl) crystal array with low cost could be applied in the fields of medical imaging and high-resolution gamma camera.

High Sensitivity and Specificity Detection of Protoporphyrin IX Fluorescence in Glioblastoma by Means of Simultaneous 2-photon Microscopy and Stimulated Raman Histology

Abstract INTRODUCTION Extent of resection has been recognized as an important predictor for survival in glioblastoma (GBM) patients. The detection of residual infiltrating tumor at the time of surgery can be challenging. 5-aminolevulinic acid (5-ALA) has recently been approved for the visualization of malignant tissue during glioma surgery. A limitation of such optical contrast agents when imaged with standard operating microscopes is sensitivity and specificity for detecting malignant tissue with low cellularity at the infiltrative tumor margin or in low-grade gliomas. METHODS We present the use of a clinical laser microscopy system (Invenio Imaging Inc, NIO Laser Imaging System) to image fresh biopsy specimens in the OR in under 3 min based on Stimulated Raman Histology. The system was modified to simultaneously detect the 2-photon fluorescence signal of 5-ALA induced protoporphyrin IX (PpIX) fluorescence with a highly sensitive photo-multiplier tube (Hamamatsu Inc.) and a 640/70 nm emission filter (Chroma Inc.). Images were quantified with a custom cell-counter for PpIX fluorescence positive cells developed in Python. The system was validated with both 5-ALA treated and untreated invasive, human GBM xenografts. RESULTS We demonstrate for the first time the detection of PpIX positive tumor cells with single-cell sensitivity. We also demonstrate that co-use with stimulated Raman scattering to image the tissue, histology can identify auto-fluorescent background that is not associated with cells. Finally, we compared the accuracy of the automated cell-counter to manual cell-counting in a series of animals (10). CONCLUSION The combination of 2-photon fluorescence imaging of PpIX with stimulated Raman histology provides unprecedented sensitivity and specificity at the cell level. This approach may provide intraoperative real-time information for tumor detection at the infiltrative margin for maximal safe resection.

Solar autocalibrating XUV-IR spectrometer system (SOLACER) for the measurement of solar spectral irradiance.

The accurate measurement of solar spectral irradiance (SSI) from space is challenging because it requires a system that can reliably exclude the impact of degradation on the instruments for the full duration of a long-term mission. The new Autocalibrating XUV-IR Spectrometer System (SOLACER) presented here meets this requirement. It is a compact and moderate-cost instrument that allows repeated onboard calibration of the spectrometers (SPs) providing SSI data of significantly increased accuracy. To this end, absolute radiometers and ionization chambers with proven long-term stability serve as primary irradiance detectors to determine the absolute SSI fluxes passing through a series of narrow- and medium-band filters with updated transmission. Consecutively cross-calibrated bolometers (BOSs) and highly sensitive photomultiplier tubes are used as secondary irradiance detectors. The new SOLACER instrument is designed to cover the spectral range from about 2-2800 nm with eight planar grating SPs. Adding total solar irradiance and BOS sensors adapted to observe the Earth's infrared emission and the reflected solar radiation, the global energy budget at the top of the atmosphere can be measured to provide data of higher absolute accuracy for climate modeling, too.

Development of a YAP(Ce) camera for the imaging of secondary electron bremsstrahlung x-ray emitted during carbon-ion irradiation toward the use of clinical conditions

Low-energy x-ray imaging of the secondary electron bremsstrahlung (SEB) x-ray emitted during carbon-ion irradiation is a promising method for range estimation. However, it remains unclear whether the method can be used for imaging with the clinical dose levels of carbon-ion and whether the bremsstrahlung x-ray can be detected from the deeper part of the body. To clarify these points, we developed a new high resolution low-energy x-ray camera and conducted imaging of the SEB x-ray during the irradiation of carbon-ions of different energies and intensities. Imaging was also tried with an x-ray camera using a human-head-sized, 17 cm diameter cylindrical phantom. To develop a high resolution imaging detector for a low-energy x-ray, we used a 20 × 20 × 0.5 mm thick cerium-doped yttrium aluminum perovskite, YA1O3 (YAP(Ce)) scintillator plate, which was optically coupled to a 25 mm square high quantum efficiency (HQE) type position sensitive photomultiplier tube (PSPMT). The imaging detector was encased in a 2 cm thick tungsten container and a pinhole collimator was attached to its camera head. After evaluating the camera’s performance, SEB x-ray imaging was tried during irradiation of the carbon-ion and compared the results with a Monte Carlo simulation. We imaged the beam tracks by the SEB x-ray in real-time during irradiation of the carbon-ion and imaging and range estimation were possible even with near clinical dose level of 7.5 × 108 particles of carbon-ion. Clear images of a SEB x-ray were also obtained for a 17 cm diameter cylindrical phantom. The measured images were good agreement with the Monte Carlo simulation. We confirmed that our developed YAP(Ce) camera is promising for imaging SEB x-rays during irradiation of carbon-ions even near clinical conditions.

Construction of a High-Resolution Mobile γ-Camera System for Mammography Study

A small-field portable γ-Camera system based on a Position Sensitive Photomultiplier Tube (PSPMT) has been recently developed in our Lab. This γ-Camera system has been characterized on planar and tomographic level and exhibits high efficiency and resolution (0.95 ± 0.5 mm spatial resolution on planar imaging and 0.20μCi sensitivity on a tomographic level). Even though a portable γ-Camera system has many advantages, it shows a strong dependence from the operators hand stability which greatly affects the quality of the acquired image. To overcome these circumstances a need for a motion correction technique arises. In the present work, a simple a low cost solution to overcome this stability problem by means of commercially available equipment is proposed. It is based on the Nintendo’s Wii Remote sensors, a small handheld device which can be easily coupled to the portable camera. It comprises both, a 3D-accelerometer which reports the three detected components of the gravity acceleration and an infrared sensor for a fix-point distance evaluation. The Wii Remote sensors device is wireless and operates with modern communication protocols (Bluetooth). Based on the received accelerometer and infrared-sensor data by a DAQ system developed on the LabVIEW environment, the γ-Cameras DAQ system is capable to store all the primary parameters on an event-by-event basis and to perform the necessary motion correction in real time. Some typical image correction results are presented in the current work.