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Cowen AR, Kengyelics SM, Davies AG. Solid-state, flat-panel, digital radiography detectors and their physical imaging characteristics. Clin Radiol 2008; 63:487-98. [PMID: 18374710 DOI: 10.1016/j.crad.2007.10.014] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Revised: 10/08/2007] [Accepted: 10/21/2007] [Indexed: 10/22/2022]
Abstract
Solid-state, digital radiography (DR) detectors, designed specifically for standard projection radiography, emerged just before the turn of the millennium. This new generation of digital image detector comprises a thin layer of x-ray absorptive material combined with an electronic active matrix array fabricated in a thin film of hydrogenated amorphous silicon (a-Si:H). DR detectors can offer both efficient (low-dose) x-ray image acquisition plus on-line readout of the latent image as electronic data. To date, solid-state, flat-panel, DR detectors have come in two principal designs, the indirect-conversion (x-ray scintillator-based) and the direct-conversion (x-ray photoconductor-based) types. This review describes the underlying principles and enabling technologies exploited by these designs of detector, and evaluates their physical imaging characteristics, comparing performance both against each other and computed radiography (CR). In standard projection radiography indirect conversion DR detectors currently offer superior physical image quality and dose efficiency compared with direct conversion DR and modern point-scan CR. These conclusions have been confirmed in the findings of clinical evaluations of DR detectors. Future trends in solid-state DR detector technologies are also briefly considered. Salient innovations include WiFi-enabled, portable DR detectors, improvements in x-ray absorber layers and developments in alternative electronic media to a-Si:H.
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Fan WH, Burnett A, Upadhya PC, Cunningham J, Linfield EH, Davies AG. Far-infrared spectroscopic characterization of explosives for security applications using broadband terahertz time-domain spectroscopy. APPLIED SPECTROSCOPY 2007; 61:638-43. [PMID: 17650376 DOI: 10.1366/000370207781269701] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Broadband terahertz time-domain spectroscopy (THz-TDS) has been used to measure the far-infrared (FIR) vibrational spectra of several commonly used pure explosives, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN), and two types of plastic explosive, SEMTEX and SX2. A number of distinct absorption peaks, originating from FIR-active vibrational modes of these polycrystalline energetic materials, were observed in the frequency range 0.3-7.5 THz (10-250 cm(-1)). In addition, the temperature-dependent FIR vibrational spectra of PETN were measured between 4 K and 296 K with several well-resolved absorption peaks observed across this temperature range. We find that as the temperature is reduced, the observed absorption peaks resolve into narrower features and shift towards higher frequencies. The temperature dependence of the spectra is explained in terms of the anharmonicity of the vibrational potentials of crystalline compounds, and an empirical fit is given to describe the peak shift with temperature.
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Davies AG, Cowen AR, Kengyelics SM, Moore J, Sivananthan MU. Do flat detector cardiac X-ray systems convey advantages over image-intensifier-based systems? Study comparing X-ray dose and image quality. Eur Radiol 2006; 17:1787-94. [PMID: 17115166 DOI: 10.1007/s00330-006-0458-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Revised: 06/21/2006] [Accepted: 08/25/2006] [Indexed: 11/25/2022]
Abstract
The recent introduction of "flat-panel detector" (FD)-based cardiac catheterisation laboratories should offer improvements in image quality and/or dose efficiency over X-ray systems of conventional design. We compared three X-ray systems, one image-intensifier (II)-based system (system A), and two FD-based designs (systems B and C), assessing their image quality and dose efficiency. Phantom measurements were performed to assess dose rates in fluoroscopy and cine acquisition. Phantom dose rates were broadly similar for all systems, with all systems classified as offering "low" dose rates in fluoroscopy on standard phantoms. Patient X-ray dose rate and subjective image quality was assessed for 90 patients. Dose area product (DAP) rates were similar for all systems, except system C, which had a lower DAP rate in fluoroscopy. In terms of subjective image quality, the order of preference was (best to worst): system C, system A, system B. This study indicates that the use of an FD detector does not infer an automatic improvement in image quality or dose efficiency over II based designs. Specification and configuration of all of the components in the X-ray system contribute to the dose levels used and image quality achieved.
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Davies AG, Cowen AR, Kengyelics SM, Moore J, Pepper C, Cowan C, Sivanathan MU. X-Ray Dose Reduction in Fluoroscopically Guided Electrophysiology Procedures. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2006; 29:262-71. [PMID: 16606393 DOI: 10.1111/j.1540-8159.2006.00332.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
This study assessed the efficacy of a new dose reduction regime in fluoroscopically guided electrophysiology (EP) procedures, which included diagnostic electrophysiological investigations, radiofrequency ablation, and biventricular pacing. A modified dose regime for fluoroscopy was implemented in one of our cardiac electrophysiology laboratories. The x-ray system was programmed with a hierarchy of three fluoroscopy doses, and therefore image quality and settings. The default (lowest) dose mode was not expected to be suitable for all patient sizes or for the entirety of all procedures. Staff raised the dose level in a stepped manner as and when required to optimize the imaging requirements of the procedure. Phantom studies indicated that the low dose mode provided adequate image quality for visualizing EP catheters, while significantly lowering patient skin dose. In 52 clinical cases, questionnaires were used to assess the subjective clinical image quality. The mean image quality score for the low dose setting was rated between "adequate" and "good." The fluoroscopy dose level was raised from the lowest level for 6% of the total fluoroscopy time. Procedural Dose Area Product (DAP) meter readings were analyzed for patients prior to (n = 85) and after (n = 150) the implementation of the low dose regime and showed an overall reduction in DAP rate of 74%. The hierarchical dose regime proved to be acceptable in routine clinical practice for EP procedures, leading to significant reductions in patient doses.
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Stringer MR, Lund DN, Foulds AP, Uddin A, Berry E, Miles RE, Davies AG. The analysis of human cortical bone by terahertz time-domain spectroscopy. Phys Med Biol 2005; 50:3211-9. [PMID: 16177504 DOI: 10.1088/0031-9155/50/14/001] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Samples of cortical bone, derived from human femur, have been studied using terahertz time-domain transmission spectroscopy. The relationship between the broadband THz parameters and the previously acquired values of Young's modulus and x-ray attenuation (CT number), and the density of each bone sample, is investigated. The only significant correlation is that between THz transmission and sample density, suggesting that the potential use of THz radiation as a non-invasive probe of bone quality is limited. The spectra of absorption coefficient and refractive index are plotted over the frequency range 0.1-1.25 THz. There is evidence that the sample hydration state is a factor in the resultant THz parameters.
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Al Hussainy HAJ, Jones S, Ali F, Davies AG. Circumferential periosteal sleeve resection for limb length inequality complicated by growth plate tether. EUROPEAN JOURNAL OF ORTHOPAEDIC SURGERY AND TRAUMATOLOGY 2004; 14:195-8. [PMID: 27517193 DOI: 10.1007/s00590-004-0161-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2004] [Accepted: 05/31/2004] [Indexed: 11/29/2022]
Abstract
Correction of limb length inequality can be achieved by stimulation of growth of the short limb. Circumferential periosteal sleeve resection has been reported as a safe and reliable method of stimulating longitudinal bone growth. We report the complication of growth tethers to the distal tibial physes in two patients following circumferential periosteal sleeve resection to the distal femur, tibia and fibula. This was done under direct vision. This complication may have arisen due to damage to the perichondrial ring as a result of raising the periosteum too close to the distal tibial physes. A limited response may be seen in young patients following this procedure as a result of this complication. Circumferential periosteal sleeve resection for limb length inequality is a treatment option that is not without complication.
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Davies AG, Bettinger JC, Thiele TR, Judy ME, McIntire SL. Natural variation in the npr-1 gene modifies ethanol responses of wild strains of C. elegans. Neuron 2004; 42:731-43. [PMID: 15182714 DOI: 10.1016/j.neuron.2004.05.004] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 03/12/2004] [Accepted: 04/12/2004] [Indexed: 11/22/2022]
Abstract
Variation in the acute response to ethanol between individuals has a significant impact on determining susceptibility to alcoholism. The degree to which genetics contributes to this variation is of great interest. Here we show that allelic variation that alters the functional level of NPR-1, a neuropeptide Y (NPY) receptor-like protein, can account for natural variation in the acute response to ethanol in wild strains of Caenorhabditis elegans. NPR-1 negatively regulates the development of acute tolerance to ethanol, a neuroadaptive process that compensates for effects of ethanol. Furthermore, dynamic changes in the NPR-1 pathway provide a mechanism for ethanol tolerance in C. elegans. This suggests an explanation for the conserved function of NPY-related pathways in ethanol responses across diverse species. Moreover, these data indicate that genetic variation in the level of NPR-1 function determines much of the phenotypic variation in adaptive behavioral responses to ethanol that are observed in natural populations.
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Davies AG, McIntire SL. Using C. elegans to screen for targets of ethanol and behavior-altering drugs. Biol Proced Online 2004; 6:113-119. [PMID: 15192754 PMCID: PMC420456 DOI: 10.1251/bpo79] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2004] [Revised: 06/01/2004] [Accepted: 06/02/2004] [Indexed: 11/23/2022] Open
Abstract
Caenorhabditis elegans is an attractive model system for determining the targets of neuroactive compounds. Genetic screens in C. elegans provide a relatively unbiased approach to the identification of genes that are essential for behavioral effects of drugs and neuroactive compounds such as alcohol. Much work in vertebrate systems has identified multiple potential targets of ethanol but which, if any, of those candidates are responsible for the behavioral effects of alcohol is uncertain. Here we provide detailed methodology for a genetic screen for mutants of C. elegans that are resistant to the depressive effects of ethanol on locomotion and for the subsequent behavioral analysis of those mutants. The methods we describe should also be applicable for use in screening for mutants that are resistant or hypersensitive to many neuroactive compounds and for identifying the molecular targets or biochemical pathways mediating drug responses.
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Barkan A, Tittel FK, Mittleman DM, Dengler R, Siegel PH, Scalari G, Ajili L, Faist J, Beere HE, Linfield EH, Davies AG, Ritchie DA. Linewidth and tuning characteristics of terahertz quantum cascade lasers. OPTICS LETTERS 2004; 29:575-577. [PMID: 15035475 DOI: 10.1364/ol.29.000575] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.
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85
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Wirtz R, Wälti C, Tosch P, Pepper M, Davies AG, Germishuizen WA, Middelberg APJ. Influence of the thiol position on the attachment and subsequent hybridization of thiolated DNA on gold surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:1527-1530. [PMID: 15803746 DOI: 10.1021/la036027o] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
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Davies AG, Pierce-Shimomura JT, Kim H, VanHoven MK, Thiele TR, Bonci A, Bargmann CI, McIntire SL. A central role of the BK potassium channel in behavioral responses to ethanol in C. elegans. Cell 2004; 115:655-66. [PMID: 14675531 DOI: 10.1016/s0092-8674(03)00979-6] [Citation(s) in RCA: 269] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The activities of many neuronal proteins are modulated by ethanol, but the fundamental mechanisms underlying behavioral effects of ethanol remain unclear. To identify mechanisms responsible for intoxication, we screened for Caenorhabditis elegans mutants with altered behavioral responses to ethanol. We found that slo-1 mutants, which were previously recognized as having slightly uncoordinated movement, are highly resistant to ethanol in two behavioral assays. Numerous loss-of-function slo-1 alleles emerged from our screens, indicating that slo-1 has a central role in ethanol responses. slo-1 encodes the BK potassium channel. Electrophysiological analysis shows that ethanol activates the channel in vivo, which would inhibit neuronal activity. Moreover, behaviors of slo-1 gain-of-function mutants resemble those of ethanol-intoxicated animals. These results demonstrate that selective activation of BK channels is responsible for acute intoxicating effects of ethanol in C. elegans. BK channel activation may explain a variety of behavioral responses to ethanol in invertebrate and vertebrate systems.
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Bettinger JC, Carnell L, Davies AG, McIntire SL. The use of Caenorhabditis elegans in molecular neuropharmacology. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2004; 62:195-212. [PMID: 15530573 DOI: 10.1016/s0074-7742(04)62007-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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88
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Davies AG, Russell WC, Thompson JP. Extravasation and tissue necrosis secondary to central line infusions. Anaesthesia 2003; 58:820-1. [PMID: 12859503 DOI: 10.1046/j.1365-2044.2003.03295_26.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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89
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Shen YC, Davies AG, Linfleld EH, Elsey TS, Taday PF, Arnone DD. The use of Fourier-transform infrared spectroscopy for the quantitative determination of glucose concentration in whole blood. Phys Med Biol 2003; 48:2023-32. [PMID: 12884933 DOI: 10.1088/0031-9155/48/13/313] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Fourier-transform infrared transmission spectroscopy has been used for the determination of glucose concentration in whole blood samples from 28 patients. A 4-vector partial least-squares calibration model, using the spectral range 950-1200 cm(-1), yielded a standard-error-of-prediction of 0.59 mM for an independent test set. For blood samples from a single patient, we found that the glucose concentration was proportional to the difference between the values of the second derivative spectrum at 1082 cm(-1) and 1093 cm(-1). This indicates that spectroscopy at these two specific wavenumbers alone could be used to determine the glucose concentration in blood plasma samples from a single patient, with a prediction error of 0.95 mM.
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Abstract
Atrial fibrillation is the commonest sustained cardiac arrhythmia. It accounts for >35% of all hospital admissions for cardiac arrhythmias in the United States. The presence of atrial fibrillation increases the mortality of a population by up to twofold. The risk of stroke increases from 1.5% in patients with atrial fibrillation from 50-59 years of age to up to 23.5% for such patients aged 80-89 years. Although the diagnosis of atrial fibrillation is usually straightforward, effective treatment is not. This article will discuss how rhythm control of atrial fibrillation can best be achieved, the controversy over the rhythm versus rate control, the maintenance of sinus rhythm with antiarrhythmic drugs after cardioversion, and prevention of thromboembolism. Finally, the recent advances in various non-pharmacological approaches for the treatment of atrial fibrillation will be highlighted.
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91
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Germishuizen WA, Walti C, Tosch P, Wirtz R, Pepper M, Davies AG, Middelberg APJ. Dielectrophoretic manipulation of surface-bound DNA. ACTA ACUST UNITED AC 2003; 150:54-8. [PMID: 16468931 DOI: 10.1049/ip-nbt:20031080] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Dielectrophoretic manipulation enables the positioning and orientation of DNA molecules for nanometer-scale applications. However, the dependence of the dielectrophoretic force and torque on the electric field magnitude and frequency has to be well characterised to realise fully the potential of this technique. DNA in solution is attracted to the strongest electric field gradient (i.e. the electrode edge) as a result of the dielectrophoretic force, while the dielectrophoretic torque aligns the DNA with its longest axis parallel to the electric field. In this work, the authors attached -DNA fragments (48 and 25 kilobases) to an array of gold microelectrodes via a terminal thiol bond and characterised the orientation and elongation as a function of electric field magnitude (0.1-0.8 MVm) and frequency (0.08-1.1 MHz). Maximum elongation was observed between 200 and 500 kHz for the attached DNA. Dielectrophoresis is limited by thermal randomisation at electric fields below 0.1 MVm and by electrothermal effects above 0.7 MVm. The authors conclude that dielectrophoresis can be used to manipulate surface-immobilised DNA reproducibly.
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Abstract
The terahertz region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave. This region has not been exploited fully to date owing to the limited number of suitable (in particular, coherent) radiation sources and detectors. Recent demonstrations, using pulsed near-infrared femtosecond laser systems, of the viability of THz medical imaging and spectroscopy have sparked international interest; yet much research still needs to be undertaken to optimize both the power and bandwidth in such THz systems. In this paper, we review how femtosecond near-infrared laser pulses can be converted into broad band THz radiation using semiconductor crystals, and discuss in depth the optimization of one specific generation mechanism based on ultra-fast transport of electrons and holes at a semiconductor surface. We also outline a few of the opportunities for a technology that can address a diverse range of challenges spanning the physical and biological sciences, and note the continuing need for the development of solid state, continuous wave, THz sources which operate at room temperature.
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93
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Spike CA, Davies AG, Shaw JE, Herman RK. MEC-8 regulates alternative splicing ofunc-52transcripts inC. eleganshypodermal cells. Development 2002; 129:4999-5008. [PMID: 12397108 DOI: 10.1242/dev.129.21.4999] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Previous work has shown that C. elegans MEC-8 is a putative RNA-binding protein that promotes specific alternative splices ofunc-52 transcripts. unc-52 encodes homologs of mammalian perlecan that are located extracellularly between muscle and hypodermis and are essential for muscle development in both embryos and larvae. We show that MEC-8 is a nuclear protein found in hypodermis at most stages of development and not in most late embryonic or larval body-wall muscle. We have also found that overexpression of MEC-8 in hypodermis but not muscle can suppress certainunc-52 mutant phenotypes. These are unexpected results because it has been proposed that UNC-52 is produced exclusively by muscle. We have constructed various tissue-specific unc-52 minigenes fused to a gene for green fluorescent protein that have allowed us to monitor tissue-specificmec-8-dependent alternative splicing; we show that mec-8must be expressed in the same cell type as the unc-52 minigene in order to regulate its expression, supporting the view that MEC-8 acts directly on unc-52 transcripts and that UNC-52 must be synthesized primarily by the hypodermis. Indeed, our analysis of unc-52 genetic mosaics has shown that the focus of unc-52 action is not in body-wall muscle but most likely is in hypodermis.
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Johnston MB, Whittaker DM, Dowd A, Davies AG, Linfield EH, Li X, Ritchie DA. Generation of high-power terahertz pulses in a prism. OPTICS LETTERS 2002; 27:1935-1937. [PMID: 18033407 DOI: 10.1364/ol.27.001935] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A compact, high-power emitter of half-cycle terahertz (THz) radiation is demonstrated. The device consists of an epitaxial InAs emitter upon a GaAs prism and produces THz pulses that are 20 times more powerful than those from conventional planar InAs emitters. This improvement is a direct result of reorienting the transient THz dipole such that its axis is not perpendicular to the emitting surface.
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96
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James JJ, Davies AG, Cowen AR, O'Connor PJ. Developments in digital radiography: an equipment update. Eur Radiol 2002; 11:2616-26. [PMID: 11734969 DOI: 10.1007/s003300100828] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2000] [Revised: 12/27/2000] [Accepted: 01/02/2001] [Indexed: 10/27/2022]
Abstract
Digital X-ray imaging technology has advanced rapidly over the past few years. This review, particularly aimed at those involved in using and purchasing such technology, is an attempt to unravel some of the complexities of this potentially confusing subject. The main groups of X-ray imaging devices that are considered are digitisers of conventional radiographs, image-intensifier-based fluorography systems, photostimulable phosphor computed radiography, amorphous selenium-based technology for thorax imaging and flat-panel systems. As well as describing these different systems, we look at ways of objectively assessing their image quality. Concepts that are used and explained include spatial resolution, grey-scale bit resolution, signal-to-noise ratio and detective quantum efficiency. An understanding of these basic parameters is vital in making a scientific assessment of a system's performance. Image processing and techniques are also briefly discussed, particularly with reference to their potential effects on image quality. This review aims to provide a basic understanding of digital X-ray imaging technology and enables the reader to make an independent and educated assessment of the relative merits of each system.
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Bury RF, Cowen AR, Davies AG, Hawkridge P, Bruijns AJ, von Reth E. Initial technical and clinical evaluation of a new universal image receptor system. Eur Radiol 2001; 10:1983-7. [PMID: 11305582 DOI: 10.1007/s003300000531] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The aim of this study was to evaluate the physical performance of an experimental flat-panel digital X-ray detector plate (FDXD), and to assess its clinical potential in radiographic and fluoroscopic mode. The efficiency of the detector was assessed by calculating the low-frequency detective quantum efficiency (DQE(0)), and a measure of image quality was obtained using a threshold contrast detail detectability (TCDD) test object. A range of clinical examinations were also carried out, and the results reviewed by members of the radiology staff. The DQE(0) of the system was calculated to be almost 75%, compared with a value of approximately 20 % for modern computed radiography equipment, offering the potential for increased image quality or significant dose reduction. Measurements using the TCDD test object demonstrated a corresponding advantage for the FDXD in image quality and dose efficiency. Clinical studies are producing radiographic results which are at least the equal of the best currently available digital technology, and a limited number of examinations using fluoroscopic mode at 25 frames per second have been equally encouraging. Equipment using FDXD technology could potentially fulfill all the radiographic and fluoroscopic requirements of the digital department, with improved image quality and dose efficiency.
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98
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Micolich AP, Taylor RP, Davies AG, Bird JP, Newbury R, Fromhold TM, Ehlert A, Linke H, Macks LD, Tribe WR, Linfield EH, Ritchie DA, Cooper J, Aoyagi Y, Wilkinson PB. Evolution of fractal patterns during a classical-quantum transition. PHYSICAL REVIEW LETTERS 2001; 87:036802. [PMID: 11461579 DOI: 10.1103/physrevlett.87.036802] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2000] [Indexed: 05/23/2023]
Abstract
We investigate how fractals evolve into nonfractal behavior as the generation process is gradually suppressed. Fractals observed in the conductance of semiconductor billiards are of particular interest because the generation process is semiclassical and can be suppressed by transitions towards either fully classical or fully quantum-mechanical conduction. Investigating a range of billiards, we identify a "universal" behavior in the changeover from fractal to nonfractal conductance, which is described by a smooth evolution rather than deterioration in the fractal scaling properties.
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Lairikyengbam SK, Davies AG, Jones PD. Implementation of antithrombotic management in atrial fibrillation. Postgrad Med J 2001; 77:488. [PMID: 11464814 PMCID: PMC1760999 DOI: 10.1136/pmj.77.909.488] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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100
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Davies AG, Cowen AR, Kengyelics SM, Bury RF, Bruijns TJ. Threshold contrast detail detectability measurement of the fluoroscopic image quality of a dynamic solid-state digital x-ray image detector. Med Phys 2001; 28:11-5. [PMID: 11213916 DOI: 10.1118/1.1312814] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Solid-state digital x-ray imaging detectors of flat-panel construction will play an increasingly important role in future medical imaging facilities. Solid-state detectors that will support both dynamic (including fluoroscopic) and radiographic image recording are under active development. The image quality of an experimental solid-state digital x-ray image detector operating in a continuous fluoroscopy mode has been investigated. The threshold contrast detail detectability (TCDD) technique was used to compare the fluoroscopic imaging performance of an experimental dynamic solid-state digital x-ray image detector with that of a reference image intensifier television (IITV) fluoroscopy system. The reference system incorporated Plumbicon TV. Results were presented as a threshold detection index, or H(T)(A), curves. Measurements were made over a range of mean entrance air kerma (EAK) rates typically used in conventional IITV fluoroscopy. At the upper and mid EAK rate range (440 and 220 nGy/s) the solid-state detector outperformed the reference IITV fluoroscopy system as measured by TCDD performance. At the lowest measured EAK rate (104 nGy/s), the solid-state detector produces slightly inferior TCDD performance compared with the reference system. Although not statistically significant at this EAK rate, the difference will increase as EAK is lowered further. Overall the TCDD results and early clinical experiences support the proposition that a current design of dynamic solid-state detector produces image quality competitive with that of modern IITV fluoroscopy systems. These findings encourage the development of compact and versatile universal x-ray imaging systems based upon solid-state detector technology to support R & F and vascular/interventional applications.
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