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In this article, we propose a slice-based interactive segmentation of spectral CT datasets using a bag of features method. The data are acquired from a MARS scanner that divides up the X-ray spectrum into multiple energy bins for imaging. In literature, most existing segmentation methods are limited to performing a specific task or tied to a particular imaging modality. Therefore, when applying generalized methods to MARS datasets, the additional energy information acquired from the scanner cannot be sufficiently utilized. We describe a new approach that circumvents this problem by effectively aggregating the data from multiple channels. Our method solves a classification problem to get the solution for segmentation. Starting with a set of labeled pixels, we partition the data using superpixels. Then, a set of local descriptors, extracted from each superpixel, are encoded into a codebook and pooled together to create a global superpixel-level descriptor (bag of features representation). We propose to use the vector of locally aggregated descriptors as our encoding/pooling strategy, as it is efficient to compute and leads to good results with simple linear classifiers. A linear support vector machine is then used to classify the superpixels into different labels. The proposed method was evaluated on multiple MARS datasets. Experimental results show that our method achieved an average of more than 10% increase in the accuracy over other state-of-the-art methods.

Assessment of disease burden and drug efficacy is achieved preclinically using high resolution micro computed tomography (CT). However, micro-CT is not applicable to clinical human imaging due to operating at high dose. In addition, the technology differences between micro-CT and standard clinical CT prevent direct translation of preclinical applications. The current proof-of-concept study presents spectral photon-counting CT as a clinically translatable, molecular imaging tool by assessing contrast uptake in an ex-vivo mouse model of pulmonary tuberculosis (TB). Iodine, a common contrast used in clinical CT imaging, was introduced into a murine model of TB. The excised mouse lungs were imaged using a standard micro-CT subsystem (SuperArgus) and the contrast enhanced TB lesions quantified. The same lungs were imaged using a spectral photoncounting CT system (MARS small-bore scanner). Iodine and soft tissues (water and lipid) were materially separated, and iodine uptake quantified. The volume of the TB infection quantified by spectral CT and micro-CT was found to be 2.96 mm3 and 2.83 mm3, respectively. This proof-of-concept study showed that spectral photon-counting CT could be used as a predictive preclinical imaging tool for the purpose of facilitating drug discovery and development. Also, as this imaging modality is available for human trials, all applications are translatable to human imaging. In conclusion, spectral photon-counting CT could accelerate a deeper understanding of infectious lung diseases using targeted pharmaceuticals and intrinsic markers, and ultimately improve the efficacy of therapies by measuring drug delivery and response to treatment in animal models and later in humans.

Photon-counting spectral CT requires accurate and efficient detection of photons across the broad x-ray spectrum. MARS photon-counting spectral CT imaging is an emerging technology on the clinical horizon, providing a highly specific 3D material imaging at high spatial and energy resolution. This new modality, driven by photon-processing detectors, enables the characterization of biological tissues, their composition and physiological processes, and perform a quantified assessment of exogenously administered multiple heavy atom contrast agents simultaneously. Current research projects utilizing the MARS scanners have successfully demonstrated novel applications of photon-counting spectral imaging. The aim of this chapter is to provide an overview of MARS imaging technology and its applications of small animal and human specimens.

Images from MARS spectral CT scanners show that there is much diagnostic value from using small pixels and good energy data. MARS scanners use energy-resolving photon-counting CZT Medipix3RX detectors that measure the energy of photons on a five-point scale and with a spatial resolution of 110 microns. The energy information gives good material discrimination and quantification. The 3D reconstruction gives a voxel size of 70 microns. We present images of pre-clinical specimens, including excised atheroma, bone and joint samples, and nanoparticle contrast agents along with images from living humans. Images of excised human plaque tissue show the location and extent of lipid and calcium deposition within the artery wall. The presence of intraplaque haemorrhage, where the blood leaks into the artery wall following a rupture, has also been visualised through the detection of iron. Several clinically important bone and joint problems have been investigated including: site-specific bone mineral density, bone-metal interfaces (spectral CT reduces metal artefacts), cartilage health using ionic contrast media, gout and pseudogout crystals, and microfracture assessment using nanoparticles. Metallic nanoparticles have been investigated as a cellular marker visible in MARS images. Cell lines of different cancer types (Raji and SK-BR3) were incubated with monoclonal antibody-functionalised AuNPs (Herceptin and Rituximab). We identified and quantified the labelled AuNPs demonstrating that Herceptin-functionalised AuNPs bound to SK-BR3 breast cancer cells but not to the Raji lymphoma cells. In vivo human images show the bone microstructure. Fat, water, and calcium concentrations are quantifiable.

The aim is to perform qualitative and quantitative assessment of metal induced artefacts of small titanium biomaterials using photon counting spectral CT. The energy binning feature of some photon counting detectors enables the measured spectrum to be segmented into low, mid and high energy bins in a single exposure. In this study, solid and porous titanium implants submerged in different concentrations of calcium solution were scanned using the small animal MARS photon counting spectral scanner equipped with a polyenergetic X-ray source operated at 118 kVp. Five narrow energy bins (7-45 keV, 45-55 keV, 55-65 keV, 65-75 keV and 75-118 keV) in charge summing mode were utilised. Images were evaluated in the energy domain (spectroscopic images) as well as material domain (material segmentation and quantification). Results show that calcium solution outside titanium implants can be accurately quantified. However, there was an overestimation of calcium within the pores of the scaffold. This information is critical as it can severely limit the assessment of bone ingrowth within metal structures. The energy binning feature of the spectral scanner was exploited and a correction factor, based on calcium concentrations adjacent to and within metal structures, was used to minimise the variation. Qualitative and quantitative evaluation of bone density and morphology with and without titanium screw shows that photon counting spectral CT can assess bone-metal interface with less pronounced artefacts. Quantification of bone growth in and around the implants would help in orthopaedic applications to determine the effectiveness of implant treatment and assessment of fracture healing.

Treatment failure in cancer is often due to variation in tumour characteristics within the same tumour, or across tumour sites, or over time. At present, most cancers are staged with imaging; treatment is selected, then the patient is re-imaged to see if the treatment is working. We intend to transform that approach by using a novel non-invasive spectral imaging technology together with targeted and non-targeted gold nanoparticles to measure tumour burden as well as drug delivery. In this study, we report spectral CT imaging of four different cancer cell types (ovarian, breast, Raji cancer cells and Lewis lung carcinoma) using gold nanoparticles. We also report that drug labelled targeted gold nanoparticles can specifically target HER2+ breast cancer cells and can be quantified by a spectral scanner. MARS CT incorporated with Medipix3RX detector was used. For image acquisition, four energy thresholds were set between 18 to 118keV to detect the K-edge of gold nanoparticles. Reconstructed images in narrow energy bins were used for material decomposition. In the first study, two ovarian cancer cell lines (OVCAR5 and SKOV3) were incubated in four sizes of gold nanoparticles (18, 40, 60 and 80nm). Results indicated a high uptake of 18 and 80nm of the gold nanoparticle by SKOV3; OVCAR5 show less uptake for all four nanoparticle sizes. In the second study, Lewis lung carcinoma was implanted in C57BL mice, and 15nm non-functionalized gold nanoparticles were injected via tail vein. Gold nanoparticles were visualized and quantified (0.497mg) in the peripheral region of a tumour whilst showing tumour necrosis in the middle. The third study showed the successful cross-over experiment of gold nanoparticles labelled to two drugs, Rituximab, and Herceptin to target Raji, and breast cancer cells respectively. The findings demonstrated spectral CT has the potential to enable the imaging and quantification of nanoparticles to monitor biological or disease processes and drug delivery to specific cell types.

We describe a CMS-Medipix3RX neutron camera developed by adapting and modifying detector readout electronics developed at the University of Canterbury. The readout electronics are part of the MARS x-ray scanner used for imaging applications [1]. The neutron cameras will be used for the precise evaluation of complex radiation fields in and around the Compact Muon Solenoid (CMS) detector on the Large Hadron Collider (LHC) at CERN. This evaluation will help to ascertain the performance of various sub-systems installed in the cavern as well as to predict their useful lifetimes. Medipix3RX detector can deliver real-time images of the flux and spectral composition of different particles, including slow and fast neutrons. In this neutron camera, slow neutrons are detected using a lithium fluoride conversion layer and fast neutrons by a polypropylene layer. These produce charged particles, which are then detected by a semiconductor sensor material, silicon. We modelled the mixed-field radiation at seven Medipix detector locations in the cavern by scoring the particle travelling through the detector location using FOCUS, a Monte-Carlo simulation tool, analysing the energy as well as their angular distributions of neutrons from the result of simulations.A good agreement was observed between the average flux predicted by standard FLUKA methods and those obtained from FOCUS output data integrated over time. Also, the response function of the Medipix detectors was modelled and simulated for different thicknesses of the neutron conversion layer. An algorithm was developed for track reconstruction and recognition using cluster analysis techniques. This labels and determines the density of clusters formed by groups of particles. The CMS-Medipix detectors with their conversion layers were calibrated in the CERN neutron facility and installed in the CMS cavern at the beginning of 2018. This paper discusses the calibration of the detector installation and presents early results of radiation measurements from 2018 run.

This study aims to demonstrate that spectral CT imaging can identify and quantify inflammatory components of unstable plaque such as iron, calcium and lipid in phantoms and excised human atherosclerotic plaques. Spectral CT acquisition protocol was optimised using the MARS spectral scanner. A phantom with multiple concentrations of ferric nitrate (25, 50, 100, 200 and 400 mg/ml), hydroxyapatite (104.3, 402.3, and 603.3 mg/cm3), iodine (9 and 18 mg/ml), lipid and water was scanned followed by blood clots and excised human plaques using energy thresholds 20, 28, 36 and 44 keV at 80 kVp, 55 µA tube current and 100 ms exposure time. CT images were reconstructed in narrow energy bins. Differences in linear attenuation coefficients between different concentrations of ferric nitrate and hydroxyapatite were compared using the receiver operating characteristic (ROC) curve and considered successful if AUC≥0.8. Differentiation between iron and calcium was successful at 400mg/ml ferric nitrate and 100mg/ml hydroxyapatite (AUC≥0.9; 99% correct material identification). The optimised calibrations were implemented in blood clots and plaque scans, which successfully identified iron signal within the clots, and areas of intraplaque haemorrhage and calcification in the carotid plaque specimens.

The aim of the present study is to show that non-invasive MARS imaging can differentiate between infected and healthy pulmonary tissue using an iodine-based contrast agent at high resolution. One C57BL/6J mouse with chronic tuberculosis (TB) was euthanized with CO2 and the pulmonary tissue excised. The TB lungs were incubated in 3% iodine solution. Mouse pulmonary tissue free of TB was also excised and incubated in the iodine solution for control purposes. Calibration of the MARS scanner involved scanning a phantom containing four concentrations of iodine along with water (soft tissue) and lipid (fat). The calibration phantom, control, and TB infected tissue were imaged at four threshold energy levels (20, 27, 34, 45 keV) at a constant 60 kVp tube voltage and 90 µA tube current. Following analysis of the calibration phantom, material decomposition (MD) was applied to the pulmonary tissue samples and iodine to obtain material images. MARS Vision software was used to visualize the materials to produce 3D material images. TB granulomas are visible within the lung lobes due to the iodine uptake. The amount of iodine uptake can be measured in mg by analysis of the material images using MARS Vision. MARS imaging was able to better differentiate between infected and healthy tissue. The present study demonstrated non-invasive, photon-counting CT is capable of differentiating between infected and healthy tissue. Future studies will consider development of TB markers, or drug markers labelled with gold nanoparticles, to enhance the understanding of the basic biology and mechanisms underpinning TB, and its relevance to the phenomenon of persistence in the infected host during therapy.

Diamond detectors for radiation dosimetry were modelled using the EGSnrc Monte Carlo code to investigate the influence of electrode material and detector orientation on the absorbed dose. The small dimensions of the electrode/diamond/electrode detector structure required very thin voxels and the use of non-standard DOSXYZnrc Monte Carlo model parameters. The interface phenomena was investigated by simulating a 6 MV beam and detectors with different electrode materials, namely Al, Ag, Cu and Au, with thickens of 0.1 µm for the electrodes and 0.1 mm for the diamond, in both perpendicular and parallel detector orientation with regards to the incident beam. The smallest perturbations were observed for the parallel detector orientation and Al electrodes (Z = 13). In summary, EGSnrc Monte Carlo code is well suited for modelling small detector geometries. The Monte Carlo model developed is a useful tool to investigate the dosimetric effects caused by different electrode materials. To minimise perturbations cause by the detector electrodes, it is recommended that the electrodes should be made from a low-atomic number material and placed parallel to the beam direction.

Purpose: To evaluate the use of commercially available detector‐grade synthetic diamondfilms made via chemical vapor deposition(CVD) as x‐ ray detectors for radiotherapydosimetry.Methods: A detector was fabricated using high‐quality single crystal CVDdiamondfilms (0.5 × 3 × 3 mm3) with 0.4 mm3 sensitive volumes, which were encapsulated with PMMA. The detector was placed in a (30 × 30 × 30 cm3) PTW water phantom. Six‐ and ten‐MV photons from an Elekta Synergy linac were measured using an SSD of 90 cm and typically a 10‐cm phantom depth with a 10 × 10 cm2 field size in the central axis of the beam. Data acquisition was performed using a PTW UNIDOS E electrometer with a 100‐V bias. The detector was evaluated by measuring leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate, percent depth dose (6 and 10 MV photons) and output factors. Some measurements were compared with a Si diode detector, 0.04 and/or 0.13‐cc ion chamber(s). Results:Leakage currents were negligible (∼1 pA) given the overall average sensitivity of the material (680 nC/Gy at 100 V). Detectorcurrent rise and fall times were < 2 s. Dose measurements up to 5 Gy were linear. A slight dependence on nominal dose rates up to 500 MU/min was seen with Fowler fitting parameter delta = 0.981. Percent depth dose profiles compared well to a 0.13‐cc ion chamber up to 25 cm depths for 10‐MV photons. Output factors measured well for field widths 5‐15 cm; below 5 cm, differences are seen between all four different detectors as expected. Conclusions: The type of diamond tested has potential to be used for small field dosimetry due to its small sensitive volume and high sensitivity. Further experiments are ongoing and detector packaging is yet to be optimized.

Three in-house X-ray detectors based on diamond chemical vapor deposition (CVD) from the same manufactured batch of single crystal films were investigated for their reproducibility. Leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate and angular dependence were used to evaluate differences between detectors. Slight differences were seen in leakage currents before ( ∆ =0.92–0.94). Angular dependence was minimal (97–102% avg.). Differences in detector performance appeared to be primarily due to film thickness, which can significantly change sensitivities (nC Gy −1 ) and applied fields (V μm −1 ) for detectors with small sensitive volumes. Results suggest that preselection of CVD diamond films according to thickness in addition to material quality would be required to avoid individual calibration, which is performed for commercially available natural diamond detectors.

The performance of a synthetic diamond X-ray detector during typical clinical beam characterisation procedures was compared to the performance of standard clinical detectors; this diamond detector used a single crystal diamond film synthesised using chemical vapour deposition as its sensitive element. Measurements were performed using 6 MV photons from a Varian 600C linear accelerator. The procedures measured the dose profile with depth along the central axis in a phantom (tissue maximum ratio) for a 10 × 10 cm 2 field, variation in dose at the isocentre with field size (output factor), and dose profile across and beyond the X-ray beam (off-axis ratio) for 10 × 10 cm 2 and 1 × 1 cm 2 fields. Tissue maximum ratio values were within 0.8% of the values from a standard ion chamber, over a depth range of 1–15 cm. Output factors were measured for field sizes from 0.6 × 0.6 cm 2 to 15 × 15 cm 2 and agreed well ( 2 . Off-axis measurements showed reduced penumbral width when the lateral size of the detector was reduced by holding the diamond detector in an edge-on orientation; values were comparable to those obtained using a diode detector. Overall, these results demonstrate the potential of synthetic diamond detectors for clinical beam characterisation, particularly for small beam sizes.

We have been characterizing various sensor layers bump-bonded to Medipix detector chips. We report here characterizationthe leakage current variations of a cadmium telluride (CdTe) assembled-Medipix2 assemblyat different temperatures.Medipix detectors are being used in small animal computed tomography (CT) scanner systems known as MARS-CT. The spectroscopic imaging of a mouse and human atheroma using this system has previously been reported [1-2]. In those reports, Medipix2 detectors were used with Si and GaAs sensor layers, respectively. Cadmium telluride (CdTe) is expected to be a useful sensor layer for clinical CT imaging detectors because of its good detection efficiency for x-rays in the energy range up to 120 keV. However, Aan understanding of the detection characteristics of these sensor layers is vital to high-quality imaging. This work presents the results of inhomogeneities within the CdTe sensor, temperature variations and wrinkle pattern instability.We present leakage current variations with temperature and sensitivity inhomogeneity across the detector. This is an extension of the tests previously reported in Aamir R et al [1][3].

We describe the results from a beam test of a telescope consisting of three planes of single-crystal, diamond pixel detectors. This telescope is a prototype for a proposed small-angle luminosity monitor, the Pixel Luminosity Telescope (PLT), for CMS. We recorded the pixel addresses and pulse heights of all pixels over threshold as well as the fast-or signals from all three telescope planes. We present results on the telescope performance including occupancies, pulse heights, fast-or efficiencies and particle tracking. These results show that the PLT design concept is sound and indicate that the project is ready to proceed with the next phase of carrying out a complete system test, including full optical readout.

A prototype clinical radiation detector based on commercially available single crystal diamond film made via chemical vapor deposition was investigated to determine optimal operating parameters for clinical dosimetry. This study examined how changes in applied electric field affected dosimetric performance, and determined a preferred operating voltage within the limits of clinical dosimetry equipment. Dosimetric analysis included leakage current, response dynamics such as rise and fall times, sensitivity, polarity and dependence on dose and dose rate. The results of this study indicate a preference for using a setting of 62.5 V due to its minimal rise time of 2 s, including a faster time to equilibrium, yet sufficient sensitivity of 37 nC Gy−1, which was nearly independent of polarity. At this voltage, a wider range of dose may therefore be recorded with charge collecting instruments than at higher voltages. Additionally, no clear trend was found over the range of voltages tested when evaluating dose dependence (R2=1 for 0.78–7.8 Gy) and dose rate dependence using Fowler fitting parameter Δ (0.95≤Δ≤1.01). Leakage currents were negligible (

Sandwich-type X-ray detectors were fabricated on commercially available chemical vapour deposition diamond sourced from three manufacturers: Diamond Materials GmbH, Diamonex, and Element Six. These devices were investigated using Raman spectroscopy and 6 MV photons from a clinical linear accelerator. Parameters such as the level of the dark (leakage) current and photocurrent, necessary priming dose, linearity of photocurrent with dose rate, and device sensitivity were considered. Device characteristics vary considerably. Devices fabricated using Diamonex material required high priming doses, and displayed high dark currents, low photocurrents (and hence low X-ray sensitivity), and non-linear dose rate responses. In contrast, devices fabricated from Diamond Materials and Element Six material required lower priming doses, and displayed ‘zero’ dark currents (beyond the detection limit), higher photocurrents, and linear dose rate responses. In addition, the Element Six devices exhibited less variation in response when irradiated at different angles of incidence.

Diamond photoconductive detectors have previously been shown to be suitable for detection of deep ultraviolet nanosecond-scale pulses from excimer lasers, which are to be used in next generation lithographic systems. Using simple test circuitry and low bias voltages easily measurable responses were observed when these detectors were illuminated with laser pulses at typical laser fluence levels. However, as the laser fluence is increased the detector response appears to broaden and change shape as well as increase in magnitude. In this paper we present analysis of the response of these detectors. This analysis shows that over the laser fluence range used the magnitude of the detector response exhibited a linear response. By approximating the temporal evolution of the laser pulse and simulating the transfer characteristics of the test circuit it can be seen that the pulse broadening and shape change seen with increasing fluence can be explained by the test circuit. The shape of the detector response, therefore, closely resembles the temporal shape of the laser pulse, demonstrating that these devices are fast enough to give a true representation of 10–15 ns laser pulses at a wavelength of 193 nm.

Diamond has shown great promise for the fabrication of high sensitivity, low dark current, fast and visible-blind deep UV photodetectors. In addition to careful choice of substrate material, defect passivation treatments applied to the diamond after growth have been found to considerably enhance the detector characteristics achieved. In this paper we report on the first purposefully designed 1-D CVD diamond imaging array for the detection of nanosecond 193 nm excimer laser pulses using this approach. It is shown to perform extremely well, giving less than 2% pixel-to-pixel variation in signal response, and is fast enough to avoid any sign of charge build up during prolonged operation.

Diamond grown by chemical vapour deposition (CVD) techniques has shown great promise for the fabrication of high sensitivity, low dark current, fast and visible-blind deep UV photodetectors. In addition to the careful choice of substrate material, defect passivation treatments applied to the diamond after growth have been found to considerably enhance the detector characteristics achieved. In this paper, we report on the first purposefully designed one-dimensional CVD diamond imaging array for the detection of nanosecond 193-nm excimer laser pulses using this approach. It is shown to perform extremely well, giving less than 2% pixel-to-pixel variation in signal response, and is fast enough to avoid any sign of charge build-up during prolonged operation.

The first study of long term pulse exposure and fluence level on the performance of CVD diamond photodetectors subjected to 193 nm excimer laser radiation has been performed. Whilst diamond is considered ‘radiation hard’ it is shown that damage to detector performance can be provoked at laser fluence levels considerably below that required for graphitisation or ablation. However, the application of defect passivation treatments prior to device use acts to considerably reduce the damaging effect of the radiation, such that devices suitable for stable laser monioring applications can be realised.

Beam monitoring of excimer lasers operating at high powers in the deep ultra-violet (DUV) is becoming increasingly important, due to the rapid proliferation of these systems in micromachining, photolithography, and other areas of industrial interest. This task requires radiation-hard detectors able to operate effectively for extended periods at high laser rep-rates. DUV-visible-blind photoconductors can be fabricated on polycrystalline CVD diamond, a material that is intrinsically radiation-hard and visible-blind. However, the performance of detectors fabricated on as-grown material is insufficient to meet the requirements of many excimer laser applications. In this paper, we show that sequentially applied post-growth treatments can progressively change both the gain and speed of these devices. Charge-sensitive deep-level transient spectroscopy (Q-DLTS) and transient photoconductivity (TPC) has been used to study the effect of these treatments on the defect structure of our thin-film diamond detector material. For the first time, we report the successful operation of a diamond photoconductive device with linear bias and fluence-response characteristics at more than 1 kHz at 193 nm.

Deep UV, visible blind, photoconductive devices fabricated on polycrystalline CVD diamond using inter-digitated planar electrodes have shown promising characteristics. The 'as-fabricated' device performance is insufficient for many applications; a particularly demanding example is the monitoring of high power excimer lasers operating in the UV, which ideally require visible-blind, radiation hard fast UV detectors. However, post-growth treatments can strongly modify the performance level achieved. In this paper, we show that sequentially applied treatments can progressively change both the gain and speed of these devices. We have used charge sensitive deep level transient spectroscopy (Q-DLTS) to study the effect of these treatments on the defect structure of CVD material. For the first time, we report the realisation of diamond photoconductive devices capable of operating at more than 1 MHz at 193 nm.

Diamond grown by chemical vapour deposition (CVD) methods is thought to be ideal for the fabrication of visible blind, fast deep UV photodetectors. However, careful device design and selection of high-quality CVD thin film diamond is, in itself, insufficient for the realisation of high performance devices. Post-growth device treatments are capable of transforming the optoelectronic properties of the material such that commercially interesting devices result. In the present study we have shown that sequentially applied methane–air treatments continue to modify both the gain level and speed of the device. Three such treatments give an optimal gain level, whilst more treatments than this lead to an improved turn-off speed. For the first time we have demonstrated the successful operation of a CVD diamond photoconductive device at at least 1 kHz at 193 nm, a frequency that is required for state-of-the-art excimer laser applications at this wavelength.

Thin film diamond photodetectors are one of the most promising classes of diamond devices for commercial exploitation. Already, photoconductive devices which display extremely high levels of selectivity between deep UV and visible light, allied to good sensitivity, are becoming available. However, more advanced device designs are required if high speed operation is to be achieved alongside high sensitivity. Phototransistors are ideally suited to this application, but until recently room temperature operation of diamond field effect transistors (FETs) was not possible. This has changed with the emergence of p-type hydrogenated diamond and this paper describes the fabrication and operation of the first MESFET based diamond photodetectors (OPFETs) to be made. Optical modulation has been demonstrated and the wavelength selectivity measured. Devices respond significantly more to UV light than visible wavelengths, with gain levels of around 4. The mechanism(s) of operation are discussed.

The realisation of effective UV photodetectors from thin-film diamond requires the selection of good-quality substrate material and careful device design. However, these alone are insufficient to yield high-performance characteristics: post-growth treatments are required to modify the optoelectronic properties of the diamond. Photoconductive devices fabricated in this way can be truly blind to visible light, fast and offer high levels of photoconductive gain. The origin of these improvements has been studied using thermally stimulated current (TSC) and photoconductivity measurements. The treatments used appear to provoke extremely high carrier lifetimes, encouraging high gain whilst eradicating extrinsic photoconduction. TSC reveals that a new trap state is introduced at (Ea≈0.6 eV). A model to explain the changes in device characteristics is discussed.

We have a 1-mm-thick cadmium telluride (CdTe) sensor bump-bonded to a Medipix2 readout chip. This detector has been characterized using a poly-energetic x-ray beam. Open beam images (i.e. without an attenuating specimen between the x-ray source and the detector) have been acquired at room temperature using the MARS-CT system. Profiles of various rows and columns were analyzed for one hundred, 35-ms exposures taken with a bias voltage of -300 V (operating in electron collection mode). A region of increased sensitivity is observed around the edges of the detector. A reasonably periodic, repeatable variation in pixel sensitivity is observed. Some small regions with very low sensitivity and others with zero signals are also observed. Surrounding these regions are circular rings of pixels with higher counts. At higher flux (higher tube current in the x-ray source) there is evidence of saturation of the detector assembly. In this paper we present our understanding of the origin of these features and demonstrate the improved image quality obtained after correcting for these variations.

A phototransistor fabricated from thin-film diamond is reported. Polycrystalline diamond grown by chemical vapor deposition, which is p-type by virtue of near-surface hydrogen, has been used to realize optically activated metal–semiconductor field-effect transistors (FETs). Devices with thin (30 nm) Al Schottky gates and Au source and drain contacts operate as effective enhancement-mode metal–semiconductor field-effect transistors at room temperature; illumination of an electrically isolated gate leads to increased channel current, although saturation is still evident. At deep UV wavelengths (

Next generation photolithography stepper tools will operate at 157 nm and require robust solid state photodetectors to ensure efficient operation and facilitate direct beam monitoring for photoresist dosimetry. There is currently no commercial detector system able to fully meet all the demanding requirements of this application. Diamond has a band gap of 5.5 eV. This implies that detectors fabricated from this material may be intrinsically visible blind and radiation hard. In this paper the results of the first study to assess the viability of the use of thin film polycrystalline diamond photodetectors for use in 157 nm F2-He based laser lithography tools are presented. Co- planar interdigitated electrode structures were fabricated on free standing polycrystalline diamond to realise photoconductive devices. These were exposed to pulses from an F2-He laser in the fluence range 0 - 1.4 mJcm-2. The electrical and optical characteristics of the devices have been measured and are compared to the response of a standard vacuum photodiode. The diamond devices appear to be ideally suited for use at 157 nm in lithography applications.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Purpose: To determine optimal operating parameters of a clinical x‐ray detector based on chemical vapor deposition(CVD)diamond while using conventional dosimetry instrumentation. Method and Materials: A prototype diamonddetector was fabricated based upon commercially available single crystaldiamond (0.5 × 3 × 3 mm3) synthesized via CVD and Perspex encapsulation that was designed to adapt to an existing Solid Water phantom used for routine clinical dosimetry. 6 MV photons from a Varian 600C linear accelerator were measured using a SSD of 90 cm and 10 cm phantom depth with a 10 × 10 cm2 field size in the central axis of the beam. A 2570/1 Farmer Dosemeter and Keithley 6430 SourceMeter were used to measure dose. Response dynamics e.g. rise and fall times, sensitivity, stability, and linearity of dose and dose rate were observed as functions of operating voltage. Results:Photocurrent rise and fall times were observed as a function of operating voltage ranging from 50 to 200 V. Differences in rise times were found to be nearly negligible. A nonlinear decrease in fall times of detector current was observed, ranging from 42 to 5 s for 100 to 200 V. Average current and sensitivity as a function of voltage followed a power‐law relationship, with average sensitivity values of 276 and 474 nC Gy−1 mm3 for 100 and 200 V, respectively. Small deviations were observed in the fitting parameter Δ for photocurrent as a function of dose rate for different voltages. Conclusion: Results indicate that using voltages of 175 V and above minimize response times and provide sufficient sensitivity with negligible dark currents. However, more investigations are needed to improve temporal response, especially below 175 V. Studies of desired properties and parameters are ongoing to evaluate and optimize detector performance.

Purpose: To investigate the suitability of synthetic diamondfilms as detectors for radiotherapydosimetry.Method and Materials: A range of commercially available diamondfilms grown by chemical vapor deposition(CVD) have been studied using spectroscopic, microscopic and electrical characterization techniques, including Raman spectroscopy, optical, secondary electron, and atomic force microscopy. Diamond detectors incorporating Perspex have been fabricated in order to examine various response characteristics, especially transient behavior and priming effects, due to material defects, interface phenomena, etc. Initial dosimetric characterization was performed using a 6 MV photon beam from a Varian 600C linac. Measurements were achieved using a 2570/1 Farmer Dosimeter and a Keithley 6430 SourceMeter. EGSnrc code was used to model simple device structures to assess performance issues that may impede proper measurements e.g. sources of fluence perturbation, absorbed dose distribution, and charge collection efficiency. Results: I–V measurements of polycrystalline diamondfilms with Ag contacts tested under a ±210 V bias sweep exhibited nonlinear behavior as expected. High leakage currents were a problem for some detectors. Resistivity measurements at 100 V from one manufacturer of films spanned from 1011 to 1012 Ω⋅cm. Dependence on fluence and fluence rates between 50 – 250 MU/min was observed. However, angular dependence appeared to be negligible. Overshoot was also seen during initial exposure, as well as the well‐known priming effect as the signal evolved over time. EGSnrc models have illustrated how electrode thickness alters the dose delivered to the sensitive volume. Conclusion: Experiments will continue to explore the response phenomena of CVDdiamondfilms to evaluate their suitability as detectors for medical applications. The films studied thus far have exhibited typical behavior as seen in previous literature. A thorough characterization of a variety of CVDfilms and their consequential responses is underway in order to mitigate or ideally eliminate inherent shortcomings.