CsI Layer Research Articles

Automatic segmentation of layers in chorio-retinal complex using Graph-based method for ultra-speed 1.7MHz wide field swept source FDML optical coherence tomography.

The posterior segment of the human eye complex contains two discrete microstructure and vasculature network systems, namely, the retina and choroid. We present a single segmentation framework technique for segmenting the entire layers present in the chorio-retinal complex of the human eye using optical coherence tomography (OCT) images. This automatic program is based on the graph theory method. This single program is capable of segmenting seven layers of the retina and choroid scleral interface. The graph theory was utilized to find the probability matrix and subsequent boundaries of different layers. The program was also implemented to segment angiographic maps of different chorio-retinal layers using "segmentation matrices." The method was tested and successfully validated on OCT images from six normal human eyes as well as eyes with non-exudative age-related macular degeneration (AMD). The thickness of microstructure and microvasculature for different layers located in the chorio-retinal segment of the eye was also generated and compared. A decent efficiency in terms of processing time, sensitivity, and accuracy was observed compared to the manual segmentation and other existing methods. The proposed method automatically segments whole OCT images of chorio-retinal complex with augmented probability maps generation in OCT volume dataset. We have also evaluated the segmentation results using quantitative metrics such as Dice coefficient and Hausdorff distance This method realizes a mean descent Dice similarity coefficient (DSC) value of 0.82 (range, 0.816-0.864) for RPE and CSI layer.

Absolute calibration of the spectral sensitivity of an x-ray streak camera over the 0.1-10keV spectral range equipped with CsI photocathode.

In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1-10keV range equipped with a CsI photocathode for Laser MégaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch-Technische-Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air.

Fully Roll-to-Roll Processed Efficient Perovskite Solar Cells via Precise Control on the Morphology of PbI2:CsI Layer

HighlightsThe slot-die-coated porous PbI2:CsI film assisted with nitrogen blowing can promote the rapid and complete transformation of perovskite film.The crystallinity and morphology of slot-die-coated perovskite film are significantly improved by controlling substrate temperature.Fully slot-die-coated perovskite solar cells achieve a power conversion efficiency (PCE) of 18.13%, and fully roll-to-roll printed flexible PSCs achieve a PCE of 13.00% in ambient condition.

Design and fabrication of a CsI(Tl) micro-columnar structure scintillation film for digital dental radiography application

Recently, indirect X-ray detectors are used for digital dental radiography. An indirect X-ray detector consists of a scintillation film and an image sensor. A scintillation film is usually composed of a CsI(Tl) layer deposited on a substrate with capability of guiding light photons to the integrated CMOS sensors. In this study, we are reporting a 30 μm thickness of CsI(Tl) layer deposited on a fiber optic faceplate(FOP) by using physical vapor deposition (PVD) process. Mentioned FOP consists of optical fibers with a 6 μm core size and 11× 9× 1.46 mm3 dimension. Fabricated CsI(Tl) film was evaluated using measured and simulated criteria such as modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). Results verify a binding agreement between measured and simulated data.

From Salt to Germanene: A Cookbook for Electrochemical Formation of 2D Materials (Inspired by R. Adžić)

The re-discovery of graphene[1], until now the most studied 2D material, opened a large playground for scientists to study exotic properties of confined electrons. A few monolayers thick 2D sheets of insulating or semiconducting materials with various atomic compositions rapidly became a hot topic. Such sheets were shown to behave differently compared to their 3D counterparts, in large part due to the different electronic structure arising from the 2D nature of the material. They bear great promise for applications in electronics and optoelectronics, sensors, composite materials, photovoltaics, medicine, quantum dots, energy storage and cryptography. The most renowned 2D material is certainly graphene, but its analogs silicene and germanene have also drawn increased attention due to their potentially simpler incorporation in current semiconductor electronics. There are several means of preparation for 2D materials: exfoliation or cleavage, chemical vapor deposition (CVD) and, as recently shown, also by underpotential deposition (UPD) [2]. Because standard UPD of transition metals also effectively results in formation of 2D layers, it might therefore be possible to explain the recently observed electrochemical formation of germanene by some of the principles discovered by R. Adžić et al. regarding UPD growth. They suggested that depending on the nature of the bond within the 2D layer (ionic vs. covalent) one can perhaps predict the general 2D structure of the layer (mixed monolayer vs. bilayer) [3]. We tested this idea in both UHV and electrochemical environments and found that this suggestion indeed holds in the case of truly ionic CsI layers [4]. The CsI layers, prepared in UHV by coadsorption of Cs and iodine, undergo several phase transitions from mixed monolayer with a honeycomb motif through to a bilayer. Simple electrostatic calculations showed that this evolution is expected from a theoretical perspective. To further test the hypothesis, we also prepared 2D CsO layers which are also strongly ionic due to the high oxygen electronegativity. Indeed, the observed 2D structures are the same as in the CsI case pointing to the universality of the hypothesis proposed by R. Adžić et al. These results later sparked the idea that, by following the same principles, the honeycomb structure could be patterned onto the surface also for different elements because the presence of the anion in the electrolyte forces the layer to be deposited in the honeycomb arrangements. To show that this approach is feasible, we deposited germanium on Au(111) as the UPD has been studied before and it is still difficult to prepare germanene in UHV environment. We found that indeed the germanium deposition results in a honeycomb layer after following a certain protocol [2]. Furthermore the growth process was also characterized by STM, Raman spectroscopy and Surface X-ray diffraction (SXRD). [1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science, 306 (2004), 666–669 [2] M. Ledina, N. Bui, X. Liang, Y. -G. Kim, J. Jung, B. Perdue, C. Tsang, J. Drnec, F. Carla, M. P. Soriaga, T. J. Reber, J. L. Stickney, J. Electrochem. Soc., 164 (2017), D469-D477 [3] J. X. Wang, I. K. Robinson, J. E. DeVilbiss and R. Adžić, J. Phys. Chem. B, 104 (2000), 7951–7959 [4] J. Drnec and D. A. Harrington, Surface Science, 604 (2010), 2106–2115; J. Drnec and D. A. Harrington, Surface Science, 630 (2014), 9-15

MPGD-based photon detector upgrade for COMPASS RICH

The RICH detector of the COMPASS Experiment at CERN SPS is undergoing an important upgrade: the central MWPC-based photon detectors have been replaced with novel Micropattern detectors, to cope with the challenging efficiency and stability requirements of the new COMPASS measurements. The new hybrid MPGD detector consists of two layers of ThickGEMs and a capacitive bulk Micromegas. Photoconversion takes place on the CsI layer deposited onto the first ThickGEM, while position information and signals are read out from the pad-segmented anode via capacitive coupling by analog front-end electronics based on APV25 chips. The paper focuses on the main issues of production, detailed quality assessment technique, and the commissioning status of the first in-experiment MPGD-based photon detectors for RICH application.

Impact of Lubberts Effect on Amorphous Selenium Indirect Conversion Avalanche Detector for Medical X-Ray Imaging

The exponential X-ray absorption makes the indirect conversion X-ray image sensors vulnerable to the Lubberts effect, which in turn makes the sensor more sensitive to the electronic noise. A cascaded linear-system model is proposed to find the required electric field to overcome the effect of electronic noise and depth dependent X-ray absorption (Lubberts effect) in amorphous selenium indirect conversion avalanche detectors. The model also includes scattering due to ${ {K}}$ -fluorescence reabsorption. The effect of depth dependent X-ray absorption is more pronounced in thicker detectors. It is observed that, at the Nyquist frequency ( ${ {f}}_{ {N}}$ ) of 2.5 mm $^{-1}$ , the presampling modulation transfer function of CsI deteriorates from 0.75 to 0.1 due to Lubberts effect in a CsI layer having thickness of 0.6 mm. The detective quantum efficiency (DQE) at ${ {f}}_{ {N}}$ (2.5 mm $^{-1}$ ) drops from 0.037 to 0.01 at a field of 60 V/ ${ {\mu } }\text{m}$ due to Lubberts effect. The Lubberts fraction decreases with increasing the field thereafter. The avalanche gain enhances the signal strength and improves the frequency dependent DQE $({ {f}})$ by overcoming the Lubberts effect and as well as the effect of the electronic noise. An avalanche gain of 45 is sufficient to overcome the effect of the electronic noise.

Effect of Deposition Temperature on Optical and Crystallographic Properties of CsI Thick Films Deposited using Spray Pyrolysis

A deposited layer of CsI has been prepared at different substrate temperatures using spray pyrolysis technique. The X Ray diffraction of CsI films reveals special pattern peaks (110), (200), (211), (220), (310) and (321). From transmission spectra we calculated the energy gap of CsI films which increase with increasing deposition temperature for direct transition is estimated.

Gamma-quanta and charged particles recognition by the counting and triggers signals formation system of GAMMA-400 space gamma-telescope

Registered events identification procedures details in three apertures of gamma-telescope GAMMA-400 are discussed in the presented article for gammas, electrons/positrons and protons both in low and high energy bands. Gamma-telescope GAMMA-400 consists of the converter-tracker (C) surrounded by anticoincidence system, time-of-flight system (2 sections S1 and S2) and calorimeter. Anticoincidence system will make of top and lateral sections - ACtop and AClat, time-of-flight system TOF contain 2 segments S1 and S2. Calorimeter consists of position-sensitive calorimeter CC1 makes of 2 strips layers and 2 layers of CsI(Tl) detectors and electromagnetic calorimeter CC2 composed of CsI(Tl) crystals surrounded by plastic lateral detectors LD. Scintillation detectors of the calorimeter S3 and S4 placed correspondingly between CC1 and CC2 and after electromagnetic calorimeter. All segments of detector systems ACtop, AClat, S1-S4, LD composed of two BC-408 based sensitive layers thickness of 1 cm each. Events registration both from upper and lateral directions provides due three apertures: main, additional and lateral. GAMMA-400 parameters are optimized for detection of gamma-quanta with the energy ∼ 100 GeV in the main aperture. Gammas, electrons/positrons and protons recognition in main aperture provides due energy deposition analysis in individual detectors of ACtop, AClat, S1-S3 and CC1 individual scintillator detectors discriminators. Particles identification in the additional aperture supplied by study of energy deposition in the individual detectors S2, S3 and position-sensitive calorimeter individual scintillator detectors discriminators. In the lateral aperture low energy (0.2 - 100 MeV) photons classified by using simple anticoincidence signals from the individual detectors of LD and CC2. Higher energies γ-quanta (E>100 MeV) recognized using energy deposition analysis in the individual detectors of S3, S4, LD and CC2.

Gamma-quanta onboard identification in the GAMMA-400 experiment using the counting and triggers signals formation system.

GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) will be the new generation satellite gamma-observatory. Gamma-telescope GAMMA-400 consists of anticoincidence system (top and lateral sections - ACtop and AClat), the converter-tracker (C), time-of-flight system (2 sections S1 and S2), position-sensitive calorimeter CC1 makes of 2 strips layers and 2 layers of CsI(Tl) detectors, electromagnetic calorimeter CC2 composed of CsI(Tl) crystals, neutron detector ND, scintillation detectors of the calorimeter (S3 and S4) and lateral detectors of the calorimeter (LD). All detector systems ACtop, AClat, S1-S4, LD consist of two BC-408 based sensitive layers of 1 cm thickness each. Three apertures provide events registration both from upper and lateral directions. The main aperture provides the best angular (all strip layers information analysis) and energy (energy deposition in the all detectors studying) resolution. Gamma-telescope GAMMA-400 is optimized for the gamma-quanta and charged particles with energy 100 GeV detection with the best parameters in the main aperture. Triggers in the main aperture will be formed using information about particle direction provided by time of flight system and presence of charged particle or backsplash signal formed according to analysis of energy deposition in combination of both layers anticoincidence systems ACtop and AClat individual detectors. For double-layer ACtop taking into account both amplitude and temporal trigger marker onboard analysis only 2.8% photons will be wrongly recognized as electrons or protons for 100 GeV particles. The part of charged particles mistakenly identified as gammas is ∼10-5 using described algorithms. For E∼3 GeV less than 3% photons will be wrongly recognized as charged particles and fraction of wrongly identified charged particles will be also ∼10-5. In the additional aperture the particles identification is provided by analysis of signals corresponding to energy deposition in the individual detectors S2, S3 and fast signals from CC1 individual detectors discriminators. Low energy (0.2 - 10 MeV) photons in the lateral aperture recognizing by using simple anticoincidence signals from the individual detectors of LD. Gamma-quanta of higher energies are identified using energy deposition in the individual detectors of S3, S4, LD and fast signals from CC2 individual detectors discriminators. The results of anticoincidence system individual detectors thresholds modelling are discussed.

Performance assessment of CsI(Tl) screens on various substrates for X-ray imaging**Supported by National Key Scientific Instrument and Equipment Development Project (2011YQ03011205, 2013YQ03062902) and Key Program of the National Natural Science Foundation of China (U1332202)

Thallium-doped cesium iodide (CsI(Tl)) screens are widely used in X-ray imaging devices because of the columnar structure of the CsI(Tl) layer, but few reports focus on the optical role of the substrate in the screen system. In this paper, four substrates including fused silica (SiO2), silver-film coated SiO2, graphite (C) and fiber optic plate (FOP) are used to fabricate CsI(Tl) screens by thermal evaporation. Their imaging performance is evaluated by relative light output (RLO), modulation transfer function (MTF), normalized noise power spectrum (NNPS) and noise equivalent quanta (NEQ). The results reveal that although CsI(Tl) film on graphite plate yields images with the lowest light output, it presents relatively higher spatial resolution and better signal-to-noise characteristics. However, films on SiO2 plate obtain low MTF but high NNPS curves, whether they are coated with silver film or not. Furthermore, scintillation screens on FOP have bright images with low NNPS and high NEQ, but have the lowest MTF. By controlling the substrate optical features, CsI(Tl) films can be tailored to suit a given application.

SU‐E‐I‐11: Cascaded Linear System Model for Columnar CsI Flat Panel Imagers with Depth Dependent Gain and Blur

Purpose:To implement a depth dependent gain and blur cascaded linear system model (CLSM) for optimizing columnar structured CsI indirect conversion flat panel imager (FPI) for advanced imaging applications.Methods:For experimental validation, depth dependent escape efficiency, e(z), was extracted from PHS measurement of different CsI scintillators (thickness, substrate and light output). The inherent MTF and DQE of CsI was measured using high resolution CMOS sensor. For CLSM, e(z) and the depth dependent MTF(f,z), were estimated using Monte Carlo simulation (Geant4) of optical photon transport through columnar CsI. Previous work showed that Monte Carlo simulation for CsI was hindered by the non‐ideality of its columnar structure. In the present work we allowed variation in columnar width with depth, and assumed diffusive reflective backing and columns. Monte Carlo simulation was performed using an optical point source placed at different depth of the CsI layer, from which MTF(z,f) and e(z) were computed. The resulting e(z) with excellent matching with experimental measurements were then applied to the CLSM, Monte Carlo simulation was repeated until the modeled MTF, DQE(f) also match experimental measurement.Results:For a 150 micron FOS HL type CsI, e(z) varies between 0.56 to 0.45, and the MTF at 14 cycles/mm varies between 62.1% to 3.9%, from the front to the back of the scintillator. The overall MTF and DQE(f) at all frequencies are in excellent agreement with experimental measurements at all frequencies.Conclusion:We have developed a CLSM for columnar CsI scintillators with depth dependent gain and MTF, which were estimated from Monte Carlo simulation with novel optical simulation settings. Preliminary results showed excellent agreement between simulation results and experimental measurements. Future work is aimed at extending this approach to optimize CsI screen optic design and sensor structure for achieving higher DQE(f) in cone‐beam CT, which uses high kVp.

Creation of leak-proof silicon carbide diffusion barriers by means of pulsed laser deposition

TRISO (tristructural isotropic) coated fuel particles are a crucial element of the HTR safety concept. While TRISO coated particles have been proven as a very efficient barrier for a large range of fission products in HTR experimental reactors, some particular fission products could still diffuse at a considerable rate. Most importantly, radioactive silver 110mAg was found to be released from coated particles. In future HTRs with active components like a gas turbine in the primary circuit, such silver contamination may severely limit maintainability of these parts with the result of reduced life-time performance.So far, experimental analyses on silver diffusion through silicon carbide have led to contradictory results. In this work, an alternative method was used to generate silicon carbide layers as a basis for analysis of silver diffusion. With pulsed laser deposition (PLD), it is possible to generate coatings of different materials and various kinds of compounds. In particular, this technology allows the generation of layers very well defined with respect to their composition, purity and density. The microstructure can precisely be manipulated through various parameters. Based on different silicon carbide coatings with well-defined properties, we are going to investigate the silver diffusion process. Our goal is to derive the properties of an ideal silicon carbide coating preventing silver diffusion entirely.In this paper we present the major aspects of our work creating crystalline SiC layers as well as silver and CsI layers both on plane and spherical substrates. Analyses with X-ray diffraction, X-ray spectrometry and secondary ion mass spectrometry show that complex multilayer systems comprising a graphite substrate, a crystalline SiC layer and an intermediate silver layer were successfully created. Major challenges to approach in the future are the handling of high-level intrinsic stresses forming in the layer structure as well as the high vapour pressure of silver and CsI, complicating subsequent crystalline SiC coating.

Performance of columnar CsI(Tl) scintillation films prepared on special pre-deposited layers

CsI(Tl) scintillation films are widely used for X-ray imaging because their micro-columnar structure can decrease the lateral spreading of scintillating light. But the CsI(Tl) films usually show a disorder structure near the interface of the substrate and film. In this work, CsI(Tl) scintillation films were prepared on the substrates covered by a special pre-deposited CsI layer. This pre-deposited layer shows the morphology of isolated islands with uniform distribution which is caused by solid-state dewetting. The inter-island distance is determined by the initial film thickness. It is found that the columns of the CsI(Tl) films deposited on the pre-deposited layer grew from bottom to the top without disorder. The column diameter is determined by the inter-island distance. The XRD patterns of the films show only [100] preferred orientation which was the same as those of the pre-deposited layers. The performances of the films including light output and spatial resolution have been improved when the films are prepared on this kind of special pre-deposited layers.

Real-time pulse-shape discrimination and beta–gamma coincidence detection in field-programmable gate array

A real-time FPGA-based algorithm has been developed and tested to discriminate pulse-shapes, identify beta–gamma coincidence events and collect energy spectra from xenon radioisotopes using a phoswich detector. The detector consists of a thin plastic scintillator (BC-400) to detect beta and conversion electrons, a CsI(Tl) crystal for measuring X-rays and gamma-rays, and a BGO crystal, which surrounds the CsI(Tl) layer, to identify scattered photons and ultimately to reduce Compton continuum in the gamma energy spectrum. In this paper, we report on the detail of the FPGA hardware design, the pulse-shape discrimination method, and the system's operational modes. In addition, our initial real-time radioxenon measurement results with the phoswich detector are presented.

Monte Carlo performance on the x‐ray converter thickness in digital mammography using software breast models

In x-ray mammography, some of the components that play significant role to early diagnosis are the x-ray source, the breast composition as well as the composition of the x-ray converter. Various studies have previously investigated separately the influence of breast characteristics and detector configuration on the optimization of mammographic imaging systems. However, it is important to examine the combined effect of both components in improving the signal transfer properties in mammography systems of the mammograms. In the present study, the authors compared and evaluated x-ray converters using software breast models and realistic mammographic spectra in terms of: (a) zero-frequency detective quantum efficiency (DQE) and (b) sensitivity. The impact of x-ray converter thickness on contrast threshold (C(TH)) for observer assessment, based on the Rose model, was demonstrated as well. Monte Carlo techniques were applied to simulate the x-ray interactions within the software breast phantoms and thereafter within the detective medium. Simulations involved: (a) two mammographic x-ray spectra: 28 kV Mo, 0.030 mm Mo, and 32 kV W, 0.050 mm Rh of different entrance surface air kerma (ESAK: 3-7 mGy), (b) realistic breast models (dense and fatty) and (c) x-ray converter materials most frequently considered in investigations on energy integrating digital mammography detectors: the Gd(2)O(2)S:Tb granular phosphor, the CsI:Tl structured phosphor, and the a-Se photoconductive layer. Detector material thickness was considered to vary in the range from 50 mg∕cm(2) up to 150 mg∕cm(2). The Monte Carlo study showed that: (a) the x-ray beam becomes less penetrating after passing through dense breasts leading to higher values of zero-frequency DQE of the x-ray imaging converters and improved C(TH) values in all cases considered, (b) W∕Rh target∕filter combination results in improved C(TH) values at higher ESAK values, and (c) a-Se shows higher zero-frequency DQE values than the phosphor-based converters, Gd(2)O(2)S:Tb and CsI:Tl. However, thicker layers of CsI:Tl could be comparable to a-Se layers achieving approximately 27.6% C(TH) improvement at a thickness of 150 mg∕cm(2). The present Monte Carlo investigation indicates that in the energy range employed in mammography, an upper limit, approximately 100 mg∕cm(2), should be considered in the development of thicker a-Se converters. On the other hand, above this thickness value, CsI:Tl converter could improve its imaging performance.

Schottky solar cells based on CsSnI3 thin-films

We describe a Schottky solar cell based on the perovskite semiconductor CsSnI3 thin-film. The cell consists of a simple layer structure of indium-tin-oxide/CsSnI3/Au/Ti on glass substrate. The measured power conversion efficiency is 0.9%, which is limited by the series and shunt resistance. The influence of light intensity on open-circuit voltage and short-circuit current supports the Schottky solar cell model. Additionally, the spectrally resolved short-circuit current was measured, confirming the unintentionally doped CsSnI3 is of p-type characteristics. The CsSnI3 thin-film was synthesized by alternately depositing layers of SnCl2 and CsI on glass substrate followed by a thermal annealing process.

BN-Substituted fullerenes C60−2x (BN) x : a computational 11B and 15N NMR study

Density functional theory has been used to investigate the 15N and 11B NMR parameters of heterofullerenes C60−2x(BN)x (x = 1, 2, 3, 6, 9, 12, 15, 18, 21, and 24). Geometry structures of all the BN-substituted fullerenes have been optimized at the B3LYP/6-31+G* level of theory. Afterward, 11B and 15N chemical shielding isotropy and anisotropy (CSI, CSA) parameters have been calculated at the same level. The obtained results illustrate the electrostatic environment divisions of the nuclei into few layers, which have been then confirmed by calculating natural charges at B and N sites. A good correlation has been seen between the layers of CSI and CSA values and three local structures around boron and nitrogen atoms. The effects of curvature of fullerene structure on chemical shielding (CS) parameters of heterofullerenes have also been investigated by computing CS tensors for curved and relaxed structures of a set of small fragments separated from the heterofullerenes, suggesting high sensitivity of CS parameters to the curvature of fullerene structure.

Development of a large-angle pinhole gamma camera with depth-of-interaction capability for small animal imaging

A large-angle gamma camera was developed for imaging small animal models used in medical and biological research. The simulation study shows that a large field of view (FOV) system provides higher sensitivity with respect to a typical pinhole gamma cameras by reducing the distance between the pinhole and the object. However, this gamma camera suffers from the degradation of the spatial resolution at the periphery region due to parallax error by obliquely incident photons. We propose a new method to measure the depth of interaction (DOI) using three layers of monolithic scintillators to reduce the parallax error. The detector module consists of three layers of monolithic CsI(Tl) crystals with dimensions of 50.0 × 50.0 × 2.0 mm3, a Hamamatsu H8500 PSPMT and a large-angle pinhole collimator with an acceptance angle of 120°. The 3-dimensional event positions were determined by the maximum-likelihood position-estimation (MLPE) algorithm and the pre-generated look up table (LUT). The spatial resolution (FWHM) of a Co-57 point-like source was measured at different source position with the conventional method (Anger logic) and with DOI information. We proved that high sensitivity can be achieved without degradation of spatial resolution using a large-angle pinhole gamma camera: this system can be used as a small animal imaging tool.

A high resolution Small Field Of View (SFOV) gamma camera: a columnar scintillator coated CCD imager for medical applications

We describe a high resolution, small field of view (SFOV), Charge Coupled Device (CCD) based camera for imaging small volumes of radionuclide uptake in tissues. The Mini Gamma Ray Camera (MGRC) is a collimated, scintillator-coated, low cost, high performance imager using low noise CCDs. The prototype MGRC has a 600 μm thick layer of columnar CsI(Tl) and operates in photon counting mode using a thermoelectric cooler to achieve an operating temperature of - 10°C. Collimation was performed using a pin hole collimator. We have measured the spatial resolution, energy resolution and efficiency using a number of radioisotope sources including 140 keV gamma-rays from 99mTc in a specially designed phantom. We also describe our first imaging of a volunteer patient.