R. Speller - Academia.edu (original) (raw)
Papers by R. Speller
Manufacturing Letters, 2019
This paper reports on a novel technique for rapid and cost effective manufacture of bespoke X-ray... more This paper reports on a novel technique for rapid and cost effective manufacture of bespoke X-ray shielding. This technique is particularly well suited for producing prototypes of complex collimators for proof of concept and/or short duration usage. Instead of heavily investing in state-of-the-art 3D metal printing to create X-ray collimators, a conventional plastic 3D printer was used to create a hollow shell of the correct geometry which was filled with tungsten powder as the X-ray attenuating material. In this paper we have applied this technique to produce a complex collimator for energy dispersive X-ray diffraction (EDXRD), which could not be manufactured using conventional machining methods. We compare the performance of this collimator to a solid tungsten 3D printed example of the same design. EDXRD shows that the two collimators have very similar performance with the backfilled collimator having marginally worse peak resolution in momentum transfer, which is attributed to X-ray transmission through the plastic walls and the much lower packing fraction of the tungsten powder. This technique is widely accessible and is capable of rapid prototyping complicated collimator designs, whilst at 1% the cost of using a 2 tungsten 3D printing technique.
The British Journal of Radiology, 1998
Ultrasound measurements have been proposed as a means of providing structural information on bone... more Ultrasound measurements have been proposed as a means of providing structural information on bone but have also been shown to correlate with density. High correlation coefficients have been obtained in vitro, but are lower for in vivo work. The aim of this study was to investigate the relationship of broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness, to bone mineral density (BMD) measured in the calcaneus at a closely matched region of interest (ROI). Measurements were made in 55 post-menopausal and 20 young, normal women. Calcaneus BMD measurements were made using an ROI (fixed by reference to external axes) to represent the area and location of the ultrasound transducers and an ROI based on anatomical markers, positioned in the posterior part of the calcaneus. BUA was significantly correlated with calcaneus BMD in the fixed ROI (r = 0.77, p < 0.0001) and the anatomical ROI (r = 0.78, p < 0.0001). Correlation of BUA with axial BMD was lower at r = 0.63, p < 0.0001 for the spine (L2-L4) and r = 0.59, p < 0.0001 for the femoral neck. Results for SOS and stiffness were very similar. From the calcaneus dual energy X-ray absorptiometry (DXA) scan images the region representing the ultrasound measurement area was found to contain cortical bone edges in 60% of cases. In 16% of scans a small part (4.5 +/- 4.0%) of the ROI measurement area fell partially outside the heel. However, there was no obvious discrepancy in the ultrasound results in the individual cases where this occurred. The correlation between calcaneus BMD and BUA was improved from r = 0.72 to r = 0.86 when scans with a cortical edge in the measurement ROI were excluded. The values for SOS were similar. In summary, BMD of the calcaneus, when closely matched to the site of ultrasound measurement shows significant correlation with ultrasound measurements. By excluding scans in which the ultrasound measurement appeared to include bone edges, correlations of approximately r = 0.86 were obtained. However, the BMD result still does not explain all of the variance in the ultrasound results.
The British Journal of Radiology, 1999
Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA... more Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA) in four different regions of the calcaneus in 20 pre-menopausal and 55 post-menopausal women, none of whom were on treatment or suffering from conditions affecting bone. The total body option in the small animal software package of a Lunar DPX-L bone densitometer was used. The precision of the technique (%CV) varied from 0.7 to 2.2% depending on the region scanned. For post-menopausal women, BMD results in the mid and posterior parts of the calcaneus varied by < 7% while BMD in the anterior region was about 20% lower. DXA of the calcaneus was compared with measurements at the spine (L2-L4) and hip (femoral neck) and changes with age were estimated from cross-sectional data. BMD of the calcaneus was significantly reduced in 28 post-menopausal women with low lumbar spine BMD (-2SD) compared with women with normal spine BMD. Calcaneal BMD was significantly correlated to axial BMD (r = 0.45-0.77) and to age (r = 0.45 to -0.63). For a subgroup of 33 post-menopausal women measured twice after approximately 1 year, calcaneus BMD decreased by between 1.2% and 2.5% while axial BMD showed no significant change. Unlike spine or femoral neck BMD, the decrease in calcaneus BMD was significantly greater in women with low spine BMD than in normal women, possibly indicating improved detection of skeletal changes. The optimum measurement sites for BMD in the calcaneus were within the mid or posterior part of the calcaneus or enclosing the whole posterior calcaneus. The calcaneus was shown to be a precise, sensitive and simple measurement site suitable for the assessment of osteoporosis, especially in the elderly where degenerative changes in the spine and hip can complicate BMD assessment.
Journal of Instrumentation, 2012
The current study uses a novel large area (12.8 cm × 13.1 cm) complementary metal-oxide-semicondu... more The current study uses a novel large area (12.8 cm × 13.1 cm) complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) X-ray detector, named Dynamic range Adjustable for Medical Imaging Technology (DynAMITe), for breast cancer diagnosis. The detector consists of two geometrically superimposed grids: a) 2560 × 2624 fine-pitch grid of pixels (50 μm pitch), named Sub-Pixels (SP camera), for low intrinsic noise and high spatial resolution and b) 1280 × 1312 large-pitch grid of pixels (100 μm pitch), named Pixels (P camera), for high dynamic range. X-ray performance characterization measurements show that the detective quantum efficiency (DQE) of the SP camera is in the range 0.7–0.75 at low spatial frequencies using a tungsten (W) anode X-ray source at 28 kV. Hence, the detector is suitable for mammography. Furthermore, we used the SP camera to combine mammograms with angle dispersive X-ray diffraction (ADXRD) measurements in order to apply the X-ray biopsy concept in one examination. The results show that ADXRD technique indicates the presence of cancer in suspicious areas on the mammogram. Hence, it could be used to determine the region affected by cancer and assist in planning surgery. This study is the proof of concept that mammography and ADXRD can be combined in one examination.
2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2014
DynAMITe (Dynamic range Adjustable for Medical Imaging Technology) is a recently developed wafer ... more DynAMITe (Dynamic range Adjustable for Medical Imaging Technology) is a recently developed wafer scale (12.8 cm × 13.1 cm) X-ray detector consisting of a Complementary Metal-Oxide-Semiconductor (CMOS) Active Pixel Sensor (APS) coupled to a 150 μm Thallium-activated Cesium Iodide (CsI:Tl) screen. It consists of two cameras: a Sub-Pixel (SP) camera with 50 μm pitch and a Pixel (P) camera with 100 μm pixel pitch. Each camera can support multiple Regions of Interest (ROIs). The combination of different settings (reset voltages, frame rates and destructive or non-destructive readout) for the two cameras allows DynAMITe to achieve a high dynamic range in comparison to other CMOS devices. Mean-Variance analysis was used in this paper to characterise the detector using different reset voltages. A commercial X-ray source was used instead of optical light to perform the Mean-Variance analysis. Overall gain instead of conversion gain can be measured using this method. However, by using a cascaded linear system model, the conversion gain of the detector using different reset voltage can also be estimated. The experimental results have shown that by combining the two cameras at different reset voltages, the dynamic range can be increased to 93.7 ± 0.2 dB from 66.7 ± 0.4 dB (SP) and 66.8±0.1 (P).
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
One way of smuggling drugs into a country is via the postal and courier services. Automated syste... more One way of smuggling drugs into a country is via the postal and courier services. Automated systems are necessary to scan incoming parcels and make quick decisions on whether they contain drugs or not. Few false positive and negative results are an important requirement for the end users of such a system, as neither parcels containing drugs should be lost
Medical Imaging 2012: Physics of Medical Imaging, 2012
ABSTRACT X-ray diffraction studies are used to identify specific materials. Several laboratory-ba... more ABSTRACT X-ray diffraction studies are used to identify specific materials. Several laboratory-based x-ray diffraction studies were made for breast cancer diagnosis. Ideally a large area, low noise, linear and wide dynamic range digital x-ray detector is required to perform x-ray diffraction measurements. Recently, digital detectors based on Complementary Metal-Oxide- Semiconductor (CMOS) Active Pixel Sensor (APS) technology have been used in x-ray diffraction studies. Two APS detectors, namely Vanilla and Large Area Sensor (LAS), were developed by the Multidimensional Integrated Intelligent Imaging (MI-3) consortium to cover a range of scientific applications including x-ray diffraction. The MI-3 Plus consortium developed a novel large area APS, named as Dynamically Adjustable Medical Imaging Technology (DynAMITe), to combine the key characteristics of Vanilla and LAS with a number of extra features. The active area (12.8 × 13.1 cm2) of DynaMITe offers the ability of angle dispersive x-ray diffraction (ADXRD). The current study demonstrates the feasibility of using DynaMITe for breast cancer diagnosis by identifying six breast-equivalent plastics. Further work will be done to optimize the system in order to perform ADXRD for identification of suspicious areas of breast tissue following a conventional mammogram taken with the same sensor.
Physics in medicine and biology, Jan 21, 2008
A novel x-ray phase contrast imaging technique based on coded apertures was recently developed at... more A novel x-ray phase contrast imaging technique based on coded apertures was recently developed at University College London. This technique removes most limitations of previous phase contrast methods and provides image improvements comparable to those obtained with synchrotron radiation with conventional x-ray sources. Unlike other phase contrast approaches, the technique does not impose restrictive wavelength and/or angular filtering on the beam emitted by the source, meaning that the beam can be exploited in full thus minimizing exposure times. As a consequence, the method provides, for the first time, a concrete opportunity to transfer x-ray phase contrast imaging into real medical applications. This paper discusses the image formation principles, analyses the shape and nature of the phase contrast profiles obtained and draws a significant conclusion on the role of convolution integrals in the acquisition of phase contrast patterns, applicable also to other phase contrast imaging...
SPIE Proceedings, 2009
ABSTRACT Illicit drugs are imported into countries in myriad ways, including via the postal syste... more ABSTRACT Illicit drugs are imported into countries in myriad ways, including via the postal system and courier services. An automated system is required to detect drugs in parcels for which X-ray diffraction is a suitable technique as it is non-destructive, material specific and uses X-rays of sufficiently high energy to penetrate parcels containing a range of attenuating materials. A database has been constructed containing the measured powder diffraction profiles of several thousand materials likely to be found in parcels. These include drugs, cutting agents, packaging and other innocuous materials. A software model has been developed using these data to predict the diffraction profiles which would be obtained by X-ray diffraction systems with a range of suggested detector (high purity germanium, CZT and scintillation), source and collimation options. The aim of the model was to identify the most promising system geometries, which was done with the aid of multivariate analysis (MVA). The most promising systems were constructed and tested. The diffraction profiles of a range of materials have been measured and used to both validate the model and to identify the presence of drugs in sample packages.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
We investigate the potential for replacing inorganic semiconductors with polymeric semiconductors... more We investigate the potential for replacing inorganic semiconductors with polymeric semiconductors in medical X-ray imaging applications. Polymeric semiconductors are soft and can be fabricated using techniques such as spin coating and jet printing, leading to reductions in fabrication costs for large-area arrays, easy integration of heterostructures and composite materials and the possibility of using flexible substrates. By using a combined cascaded linear systems and Monte-Carlo model to simulate the imaging system, we establish a set of semiconductor requirements for a feasible flat-panel imager (FPI). We have fabricated photodiodes and thin-film transistors (TFTs) out of a variety of polymer materials. Polymer photodiodes coupled to phosphor screens have shown a response to X-ray radiation with a good efficiency. Both transistors and photodiodes were sufficiently radiation hard for use in clinical imaging conditions. A composite phosphor-polymer material has been fabricated and has been found to be compatible with polymeric photodiodes. The composite material can be fabricated within a structure as part of the semiconductor fabrication process.
Radiotherapy and Oncology, 1995
Radiation Physics and Chemistry, 1999
Elastic scattering of x-ray photons can provide information in a number of areas of tissue analys... more Elastic scattering of x-ray photons can provide information in a number of areas of tissue analysis in medicine. This paper describes measurements made of two types of tissue to demonstrate three different areas of application:•Data are presented on the differential linear coherent scattering coefficients for healthy and diseased breast tissue with the intention that such results could be used in
Physics in Medicine and Biology, 2006
The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia ... more The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia of female rats (1.5 years of age), using synchrotron radiation microtomography. The use of a monoenergetic x-ray beam, as provided by the synchrotron facility, generates accurate 3D maps of the linear attenuation coefficient within the sample and hence gives the ability to map different chemical components. Data sets were taken at 20 keV for each bone sample and calibration phantoms. From the 3D data sets, multiple 2D slices were reconstructed with a slice thickness of approximately 28 microm and converted to Ca/P ratios using the calibration phantom results. Mean values (M +/- SD) for cortical femoral, front and rear tibias are 2.12 +/- 0.08, 1.75 +/- 0.06 and 1.94 +/- 0.07 respectively. These values were compared with those derived from different animals. Differences between the same bone sites from different animals are not significant (0.1 < p < or = 0.9) while those between different bone sites are highly significant (p < 10(-3)) demonstrating a dependence upon life style and bone use.
Physics in Medicine and Biology, 2007
X-ray phase contrast imaging is probably the most relevant among emerging x-ray imaging technique... more X-ray phase contrast imaging is probably the most relevant among emerging x-ray imaging techniques, and it has the proven potential of revolutionizing the field of diagnostic radiology. Impressive images of a wide range of samples have been obtained, mostly at synchrotron radiation facilities. The necessity of relying on synchrotron radiation has prevented to a large extent a widespread diffusion of phase contrast imaging, thus precluding its transfer to clinical practice. A new technique, based on the use of coded apertures, was recently developed at UCL. This technique was demonstrated to provide intense phase contrast signals with conventional x-ray sources and detectors. Unlike other attempts at making phase contrast imaging feasible with conventional sources, the coded-aperture approach does not impose substantial limitations and/or filtering of the radiation beam, and it therefore allows, for the first time, exposures compatible with clinical practice. The technique has been thoroughly modelled, and this paper describes the technique in detail by going through the different steps of the modelling. All the main factors influencing image quality are discussed, alongside the viability of realizing a prototype suitable for clinical use. The model has been experimentally validated and a section of the paper shows the comparison between simulated and experimental results.
Physics in Medicine and Biology, 1995
Multiparameter optimizations have been carried out for a wide range of digital mammography system... more Multiparameter optimizations have been carried out for a wide range of digital mammography system configurations and requirements, with the aim of optimizing the image quality for a given patient dose. These conditions include a range of slot widths for scanning mammography systems, exposure times from 1 to 10 s, focal spot sizes from 80 to 800 microns, a range of detector resolutions and noise levels, dose restrictions, patient thicknesses and targets, and x-ray tube targets. The influences of these on the optimum system configuration in terms of tube potential, filtration, source to patient distance and target magnification are discussed. It is demonstrated that x-ray tube power constraints can significantly restrict the optimum magnification for slot scanning systems, with the result that poor-resolution detectors are not suited for use in a scanning configuration, and that large-focal-spot-good-detector resolution combinations are more suitable. The use of a detector with increased width, raised tube potential and reduced amount of added filtration is shown to be helpful in reducing x-ray tube power limitations. It is shown that, in many cases, correct optimization can bring the detail SNR for an examination using a given detector-x-ray tube configuration to within 10-15% of the SNR achieved with the optimum combination. This gives the designer some scope to consider other factors such as cost and the implications of image size on storage space.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
Diffraction imaging is a promising technique for improving the specificity of a mammographic exam... more Diffraction imaging is a promising technique for improving the specificity of a mammographic exam. A controlled drift detector (CDD), having promising characteristics in terms of low noise and spectroscopic capability, was evaluated in its application to diffraction enhanced breast imaging (DEBI). Both transmission and diffraction images of a custom-built test object and of different meat samples were acquired and the
Medical Physics, 2007
A unified Monte Carlo and cascaded systems model for the simulation of active‐matrix flat‐panel i... more A unified Monte Carlo and cascaded systems model for the simulation of active‐matrix flat‐panel imagers is presented. With few input parameters, the model simulated the imaging performance of previously measured flat‐panel imagers with reasonable accuracy. The model is used to predict the properties of conceptual flat‐panel imagers based on organic semiconductors on plastic substrates. The model suggests that significant improvements in resolution and detective quantum efficiency could be achieved by operating such a detector in a back‐side illuminated configuration, or by employing two imaging arrays arranged face‐to‐face. The effect of semiconductor properties on the conceptual imagers is investigated. According to the model, a photodiode quantum efficiency of and dark current of less than would be satisfactory for a prototype imager, while a competitive imager would require a photodiode quantum efficiency of with a dark current of less than to be quantum limited over the radiogra...
Journal of X-Ray Science and Technology, 1992
DiEiaction studies of polyenergetic x-ray beams at low angles can be used to investigate tissues.... more DiEiaction studies of polyenergetic x-ray beams at low angles can be used to investigate tissues. Recent evidence on molecular fotm factors indicates that unique "fingerprints" exist for materials in the form of scattering information at angles between 0" and 10". We have measured low angle scattering information in the form of energy spectra using a tungsten target x-ray source. It is shown that for certain scattering angles these spectra are highly structured, where this structure can be related to tissue type. We propose that these measurements will be diagnostic for various conditions such as osteoporosis or gall stone diSeaSe.
Manufacturing Letters, 2019
This paper reports on a novel technique for rapid and cost effective manufacture of bespoke X-ray... more This paper reports on a novel technique for rapid and cost effective manufacture of bespoke X-ray shielding. This technique is particularly well suited for producing prototypes of complex collimators for proof of concept and/or short duration usage. Instead of heavily investing in state-of-the-art 3D metal printing to create X-ray collimators, a conventional plastic 3D printer was used to create a hollow shell of the correct geometry which was filled with tungsten powder as the X-ray attenuating material. In this paper we have applied this technique to produce a complex collimator for energy dispersive X-ray diffraction (EDXRD), which could not be manufactured using conventional machining methods. We compare the performance of this collimator to a solid tungsten 3D printed example of the same design. EDXRD shows that the two collimators have very similar performance with the backfilled collimator having marginally worse peak resolution in momentum transfer, which is attributed to X-ray transmission through the plastic walls and the much lower packing fraction of the tungsten powder. This technique is widely accessible and is capable of rapid prototyping complicated collimator designs, whilst at 1% the cost of using a 2 tungsten 3D printing technique.
The British Journal of Radiology, 1998
Ultrasound measurements have been proposed as a means of providing structural information on bone... more Ultrasound measurements have been proposed as a means of providing structural information on bone but have also been shown to correlate with density. High correlation coefficients have been obtained in vitro, but are lower for in vivo work. The aim of this study was to investigate the relationship of broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness, to bone mineral density (BMD) measured in the calcaneus at a closely matched region of interest (ROI). Measurements were made in 55 post-menopausal and 20 young, normal women. Calcaneus BMD measurements were made using an ROI (fixed by reference to external axes) to represent the area and location of the ultrasound transducers and an ROI based on anatomical markers, positioned in the posterior part of the calcaneus. BUA was significantly correlated with calcaneus BMD in the fixed ROI (r = 0.77, p < 0.0001) and the anatomical ROI (r = 0.78, p < 0.0001). Correlation of BUA with axial BMD was lower at r = 0.63, p < 0.0001 for the spine (L2-L4) and r = 0.59, p < 0.0001 for the femoral neck. Results for SOS and stiffness were very similar. From the calcaneus dual energy X-ray absorptiometry (DXA) scan images the region representing the ultrasound measurement area was found to contain cortical bone edges in 60% of cases. In 16% of scans a small part (4.5 +/- 4.0%) of the ROI measurement area fell partially outside the heel. However, there was no obvious discrepancy in the ultrasound results in the individual cases where this occurred. The correlation between calcaneus BMD and BUA was improved from r = 0.72 to r = 0.86 when scans with a cortical edge in the measurement ROI were excluded. The values for SOS were similar. In summary, BMD of the calcaneus, when closely matched to the site of ultrasound measurement shows significant correlation with ultrasound measurements. By excluding scans in which the ultrasound measurement appeared to include bone edges, correlations of approximately r = 0.86 were obtained. However, the BMD result still does not explain all of the variance in the ultrasound results.
The British Journal of Radiology, 1999
Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA... more Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA) in four different regions of the calcaneus in 20 pre-menopausal and 55 post-menopausal women, none of whom were on treatment or suffering from conditions affecting bone. The total body option in the small animal software package of a Lunar DPX-L bone densitometer was used. The precision of the technique (%CV) varied from 0.7 to 2.2% depending on the region scanned. For post-menopausal women, BMD results in the mid and posterior parts of the calcaneus varied by < 7% while BMD in the anterior region was about 20% lower. DXA of the calcaneus was compared with measurements at the spine (L2-L4) and hip (femoral neck) and changes with age were estimated from cross-sectional data. BMD of the calcaneus was significantly reduced in 28 post-menopausal women with low lumbar spine BMD (-2SD) compared with women with normal spine BMD. Calcaneal BMD was significantly correlated to axial BMD (r = 0.45-0.77) and to age (r = 0.45 to -0.63). For a subgroup of 33 post-menopausal women measured twice after approximately 1 year, calcaneus BMD decreased by between 1.2% and 2.5% while axial BMD showed no significant change. Unlike spine or femoral neck BMD, the decrease in calcaneus BMD was significantly greater in women with low spine BMD than in normal women, possibly indicating improved detection of skeletal changes. The optimum measurement sites for BMD in the calcaneus were within the mid or posterior part of the calcaneus or enclosing the whole posterior calcaneus. The calcaneus was shown to be a precise, sensitive and simple measurement site suitable for the assessment of osteoporosis, especially in the elderly where degenerative changes in the spine and hip can complicate BMD assessment.
Journal of Instrumentation, 2012
The current study uses a novel large area (12.8 cm × 13.1 cm) complementary metal-oxide-semicondu... more The current study uses a novel large area (12.8 cm × 13.1 cm) complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) X-ray detector, named Dynamic range Adjustable for Medical Imaging Technology (DynAMITe), for breast cancer diagnosis. The detector consists of two geometrically superimposed grids: a) 2560 × 2624 fine-pitch grid of pixels (50 μm pitch), named Sub-Pixels (SP camera), for low intrinsic noise and high spatial resolution and b) 1280 × 1312 large-pitch grid of pixels (100 μm pitch), named Pixels (P camera), for high dynamic range. X-ray performance characterization measurements show that the detective quantum efficiency (DQE) of the SP camera is in the range 0.7–0.75 at low spatial frequencies using a tungsten (W) anode X-ray source at 28 kV. Hence, the detector is suitable for mammography. Furthermore, we used the SP camera to combine mammograms with angle dispersive X-ray diffraction (ADXRD) measurements in order to apply the X-ray biopsy concept in one examination. The results show that ADXRD technique indicates the presence of cancer in suspicious areas on the mammogram. Hence, it could be used to determine the region affected by cancer and assist in planning surgery. This study is the proof of concept that mammography and ADXRD can be combined in one examination.
2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2014
DynAMITe (Dynamic range Adjustable for Medical Imaging Technology) is a recently developed wafer ... more DynAMITe (Dynamic range Adjustable for Medical Imaging Technology) is a recently developed wafer scale (12.8 cm × 13.1 cm) X-ray detector consisting of a Complementary Metal-Oxide-Semiconductor (CMOS) Active Pixel Sensor (APS) coupled to a 150 μm Thallium-activated Cesium Iodide (CsI:Tl) screen. It consists of two cameras: a Sub-Pixel (SP) camera with 50 μm pitch and a Pixel (P) camera with 100 μm pixel pitch. Each camera can support multiple Regions of Interest (ROIs). The combination of different settings (reset voltages, frame rates and destructive or non-destructive readout) for the two cameras allows DynAMITe to achieve a high dynamic range in comparison to other CMOS devices. Mean-Variance analysis was used in this paper to characterise the detector using different reset voltages. A commercial X-ray source was used instead of optical light to perform the Mean-Variance analysis. Overall gain instead of conversion gain can be measured using this method. However, by using a cascaded linear system model, the conversion gain of the detector using different reset voltage can also be estimated. The experimental results have shown that by combining the two cameras at different reset voltages, the dynamic range can be increased to 93.7 ± 0.2 dB from 66.7 ± 0.4 dB (SP) and 66.8±0.1 (P).
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
One way of smuggling drugs into a country is via the postal and courier services. Automated syste... more One way of smuggling drugs into a country is via the postal and courier services. Automated systems are necessary to scan incoming parcels and make quick decisions on whether they contain drugs or not. Few false positive and negative results are an important requirement for the end users of such a system, as neither parcels containing drugs should be lost
Medical Imaging 2012: Physics of Medical Imaging, 2012
ABSTRACT X-ray diffraction studies are used to identify specific materials. Several laboratory-ba... more ABSTRACT X-ray diffraction studies are used to identify specific materials. Several laboratory-based x-ray diffraction studies were made for breast cancer diagnosis. Ideally a large area, low noise, linear and wide dynamic range digital x-ray detector is required to perform x-ray diffraction measurements. Recently, digital detectors based on Complementary Metal-Oxide- Semiconductor (CMOS) Active Pixel Sensor (APS) technology have been used in x-ray diffraction studies. Two APS detectors, namely Vanilla and Large Area Sensor (LAS), were developed by the Multidimensional Integrated Intelligent Imaging (MI-3) consortium to cover a range of scientific applications including x-ray diffraction. The MI-3 Plus consortium developed a novel large area APS, named as Dynamically Adjustable Medical Imaging Technology (DynAMITe), to combine the key characteristics of Vanilla and LAS with a number of extra features. The active area (12.8 × 13.1 cm2) of DynaMITe offers the ability of angle dispersive x-ray diffraction (ADXRD). The current study demonstrates the feasibility of using DynaMITe for breast cancer diagnosis by identifying six breast-equivalent plastics. Further work will be done to optimize the system in order to perform ADXRD for identification of suspicious areas of breast tissue following a conventional mammogram taken with the same sensor.
Physics in medicine and biology, Jan 21, 2008
A novel x-ray phase contrast imaging technique based on coded apertures was recently developed at... more A novel x-ray phase contrast imaging technique based on coded apertures was recently developed at University College London. This technique removes most limitations of previous phase contrast methods and provides image improvements comparable to those obtained with synchrotron radiation with conventional x-ray sources. Unlike other phase contrast approaches, the technique does not impose restrictive wavelength and/or angular filtering on the beam emitted by the source, meaning that the beam can be exploited in full thus minimizing exposure times. As a consequence, the method provides, for the first time, a concrete opportunity to transfer x-ray phase contrast imaging into real medical applications. This paper discusses the image formation principles, analyses the shape and nature of the phase contrast profiles obtained and draws a significant conclusion on the role of convolution integrals in the acquisition of phase contrast patterns, applicable also to other phase contrast imaging...
SPIE Proceedings, 2009
ABSTRACT Illicit drugs are imported into countries in myriad ways, including via the postal syste... more ABSTRACT Illicit drugs are imported into countries in myriad ways, including via the postal system and courier services. An automated system is required to detect drugs in parcels for which X-ray diffraction is a suitable technique as it is non-destructive, material specific and uses X-rays of sufficiently high energy to penetrate parcels containing a range of attenuating materials. A database has been constructed containing the measured powder diffraction profiles of several thousand materials likely to be found in parcels. These include drugs, cutting agents, packaging and other innocuous materials. A software model has been developed using these data to predict the diffraction profiles which would be obtained by X-ray diffraction systems with a range of suggested detector (high purity germanium, CZT and scintillation), source and collimation options. The aim of the model was to identify the most promising system geometries, which was done with the aid of multivariate analysis (MVA). The most promising systems were constructed and tested. The diffraction profiles of a range of materials have been measured and used to both validate the model and to identify the presence of drugs in sample packages.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
We investigate the potential for replacing inorganic semiconductors with polymeric semiconductors... more We investigate the potential for replacing inorganic semiconductors with polymeric semiconductors in medical X-ray imaging applications. Polymeric semiconductors are soft and can be fabricated using techniques such as spin coating and jet printing, leading to reductions in fabrication costs for large-area arrays, easy integration of heterostructures and composite materials and the possibility of using flexible substrates. By using a combined cascaded linear systems and Monte-Carlo model to simulate the imaging system, we establish a set of semiconductor requirements for a feasible flat-panel imager (FPI). We have fabricated photodiodes and thin-film transistors (TFTs) out of a variety of polymer materials. Polymer photodiodes coupled to phosphor screens have shown a response to X-ray radiation with a good efficiency. Both transistors and photodiodes were sufficiently radiation hard for use in clinical imaging conditions. A composite phosphor-polymer material has been fabricated and has been found to be compatible with polymeric photodiodes. The composite material can be fabricated within a structure as part of the semiconductor fabrication process.
Radiotherapy and Oncology, 1995
Radiation Physics and Chemistry, 1999
Elastic scattering of x-ray photons can provide information in a number of areas of tissue analys... more Elastic scattering of x-ray photons can provide information in a number of areas of tissue analysis in medicine. This paper describes measurements made of two types of tissue to demonstrate three different areas of application:•Data are presented on the differential linear coherent scattering coefficients for healthy and diseased breast tissue with the intention that such results could be used in
Physics in Medicine and Biology, 2006
The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia ... more The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia of female rats (1.5 years of age), using synchrotron radiation microtomography. The use of a monoenergetic x-ray beam, as provided by the synchrotron facility, generates accurate 3D maps of the linear attenuation coefficient within the sample and hence gives the ability to map different chemical components. Data sets were taken at 20 keV for each bone sample and calibration phantoms. From the 3D data sets, multiple 2D slices were reconstructed with a slice thickness of approximately 28 microm and converted to Ca/P ratios using the calibration phantom results. Mean values (M +/- SD) for cortical femoral, front and rear tibias are 2.12 +/- 0.08, 1.75 +/- 0.06 and 1.94 +/- 0.07 respectively. These values were compared with those derived from different animals. Differences between the same bone sites from different animals are not significant (0.1 < p < or = 0.9) while those between different bone sites are highly significant (p < 10(-3)) demonstrating a dependence upon life style and bone use.
Physics in Medicine and Biology, 2007
X-ray phase contrast imaging is probably the most relevant among emerging x-ray imaging technique... more X-ray phase contrast imaging is probably the most relevant among emerging x-ray imaging techniques, and it has the proven potential of revolutionizing the field of diagnostic radiology. Impressive images of a wide range of samples have been obtained, mostly at synchrotron radiation facilities. The necessity of relying on synchrotron radiation has prevented to a large extent a widespread diffusion of phase contrast imaging, thus precluding its transfer to clinical practice. A new technique, based on the use of coded apertures, was recently developed at UCL. This technique was demonstrated to provide intense phase contrast signals with conventional x-ray sources and detectors. Unlike other attempts at making phase contrast imaging feasible with conventional sources, the coded-aperture approach does not impose substantial limitations and/or filtering of the radiation beam, and it therefore allows, for the first time, exposures compatible with clinical practice. The technique has been thoroughly modelled, and this paper describes the technique in detail by going through the different steps of the modelling. All the main factors influencing image quality are discussed, alongside the viability of realizing a prototype suitable for clinical use. The model has been experimentally validated and a section of the paper shows the comparison between simulated and experimental results.
Physics in Medicine and Biology, 1995
Multiparameter optimizations have been carried out for a wide range of digital mammography system... more Multiparameter optimizations have been carried out for a wide range of digital mammography system configurations and requirements, with the aim of optimizing the image quality for a given patient dose. These conditions include a range of slot widths for scanning mammography systems, exposure times from 1 to 10 s, focal spot sizes from 80 to 800 microns, a range of detector resolutions and noise levels, dose restrictions, patient thicknesses and targets, and x-ray tube targets. The influences of these on the optimum system configuration in terms of tube potential, filtration, source to patient distance and target magnification are discussed. It is demonstrated that x-ray tube power constraints can significantly restrict the optimum magnification for slot scanning systems, with the result that poor-resolution detectors are not suited for use in a scanning configuration, and that large-focal-spot-good-detector resolution combinations are more suitable. The use of a detector with increased width, raised tube potential and reduced amount of added filtration is shown to be helpful in reducing x-ray tube power limitations. It is shown that, in many cases, correct optimization can bring the detail SNR for an examination using a given detector-x-ray tube configuration to within 10-15% of the SNR achieved with the optimum combination. This gives the designer some scope to consider other factors such as cost and the implications of image size on storage space.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
Diffraction imaging is a promising technique for improving the specificity of a mammographic exam... more Diffraction imaging is a promising technique for improving the specificity of a mammographic exam. A controlled drift detector (CDD), having promising characteristics in terms of low noise and spectroscopic capability, was evaluated in its application to diffraction enhanced breast imaging (DEBI). Both transmission and diffraction images of a custom-built test object and of different meat samples were acquired and the
Medical Physics, 2007
A unified Monte Carlo and cascaded systems model for the simulation of active‐matrix flat‐panel i... more A unified Monte Carlo and cascaded systems model for the simulation of active‐matrix flat‐panel imagers is presented. With few input parameters, the model simulated the imaging performance of previously measured flat‐panel imagers with reasonable accuracy. The model is used to predict the properties of conceptual flat‐panel imagers based on organic semiconductors on plastic substrates. The model suggests that significant improvements in resolution and detective quantum efficiency could be achieved by operating such a detector in a back‐side illuminated configuration, or by employing two imaging arrays arranged face‐to‐face. The effect of semiconductor properties on the conceptual imagers is investigated. According to the model, a photodiode quantum efficiency of and dark current of less than would be satisfactory for a prototype imager, while a competitive imager would require a photodiode quantum efficiency of with a dark current of less than to be quantum limited over the radiogra...
Journal of X-Ray Science and Technology, 1992
DiEiaction studies of polyenergetic x-ray beams at low angles can be used to investigate tissues.... more DiEiaction studies of polyenergetic x-ray beams at low angles can be used to investigate tissues. Recent evidence on molecular fotm factors indicates that unique "fingerprints" exist for materials in the form of scattering information at angles between 0" and 10". We have measured low angle scattering information in the form of energy spectra using a tungsten target x-ray source. It is shown that for certain scattering angles these spectra are highly structured, where this structure can be related to tissue type. We propose that these measurements will be diagnostic for various conditions such as osteoporosis or gall stone diSeaSe.