A dinucleotide repeat polymorphism at the D4S127 locus.
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Base Sequence↗
Biomedical subjects
G T Barnes
Publications and source records attributed to G T Barnes.
Acceptance testing of radiologic systems: experience in testing 129 imaging systems at two major medical facilities.
The problems encountered in acceptance testing of newly installed imaging equipment at two major medical institutions over a 10-year period are presented. Acceptance tests were conducted in 129 newly installed imaging systems with conventional acceptance testing methods. A total of 1,132 problems were documented. Problems were classified as major or minor; there were 772 major problems and 360 minor problems. An average of six major and three minor problems were documented in each new equipment installation tested. In some instances, final payment was withheld for several months or more to ensure correction of the problems identified. This experience confirms the need of thorough acceptance testing of new imaging equipment before final payment is made to the vendor.
Alabama↗
Contrast and scatter in x-ray imaging.
The effect of scattered radiation on x-ray image contrast is reviewed. Without scatter control, the information content of x-ray images is severely compromised. Typical grid performance in general radiography and mammography and grid selection considerations are presented. Contrast can be significantly improved and patient dose reduced if more efficient methods of scatter control can be developed. This can be accomplished in chest radiography with scanning slit and improved grid techniques, in mammography with multiple scanning slit techniques, and in abdominal radiography with scanning grid techniques.
Equipment Design↗
Technical exhibits.
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Exhibitions as Topic↗
Spectral dependence of glandular tissue dose in screen-film mammography.
The average glandular tissue dose in mammography is generally determined from published tables with knowledge of the breast entrance skin exposure, x-ray tube target material, beam quality (half-value layer [HVL]), breast thickness, and breast composition. Using a carefully designed and experimentally validated Monte Carlo simulation, the authors found that average glandular dose also depends on x-ray tube voltage and, to a lesser extent, on x-ray tube voltage waveform. For currently employed molybdenum target-molybdenum filter source assemblies, a difference in dose of 10% or more is possible in estimating the average glandular dose obtained with different x-ray tube voltages but with the same HVL. Presented are normalized average glandular tissue doses in units of radiation absorbed dose per unit entrance skin exposure for different tube voltages and tube voltage waveforms as well as for different breast thicknesses and compositions and beam filtrations.
Adipose Tissue↗
Image processing in digital radiography: basic concepts and applications.
Digital x-ray images are routinely processed to enhance diagnostic information and to suppress irrelevant detail, and also to extract quantitative information. The basic concepts and terminology of image processing as it applies to x-ray projection radiography are discussed and defined. In general, the processing of an image involves one or more point, local, and/or global operations. Clinical examples of linear and nonlinear gray-scale and algebraic point operations are presented. Examples are also given of local operations. Included in the latter group are distortion corrections, misregistration corrections, linear filtering, and nonlinear filtering.
Angiography, Digital Subtraction↗
A comparison of dual-energy digital radiography and screen-film imaging in the detection of subtle interstitial pulmonary disease.
An ROC study is described which compares the performance of three types of images--conventional screen-film, single-energy digital and dual energy bone cancelled (soft tissue) digital--in detecting subtle interstitial pulmonary disease. Marginally detectable nodular and reticulonodular patterns (12 different patterns of each) were superimposed over the lungs of a frozen human chest phantom to simulate the clinical situation. The digital images were formatted on film at full size (ie, 35 cm X 43 cm). A total of 156 images (52 of each type, of which 28 were normal and 24 had simulated pathology) were used in the study and read by five experienced chest radiologists. Using a paired t-test, the areas under the individual ROC curves were compared for three combinations of images--single-energy digital and conventional, soft tissue digital and conventional, and soft tissue and single-energy digital. No statistically significant difference was observed between the conventional and single-energy digital images. The readers performed better with both conventional and single-energy digital images than with the soft tissue digital images at statistically significant levels (P = 0.05 for conventional vs. soft tissue digital and P = 0.02 for single-energy digital vs. soft tissue digital). The results suggest that there is no advantage in employing dual-energy soft tissue images to assist in diagnosing interstitial disease in the clinical setting. They also suggest that spatial resolution requirements are less demanding in digital chest systems that obtain scatter-free images than in digital systems utilizing conventional scatter control techniques.
Evaluation Studies as Topic↗
Digital imaging of the chest.
During the past several years, image acquisition in nuclear medicine, computed tomography, ultrasonography, subtraction angiography, and magnetic resonance has been by digitization. Despite these advances, research in the development of digital imaging in conventional radiography has lagged behind. Although studies with a variety of digital techniques have been carried out on several fronts, we still do not possess a method that has captured the imagination of the majority of radiologists and other physicians to a point where it could replace conventional screen-film imaging. This article reviews the current status and general principles of the technology, focusing on the four digital radiographic techniques that have shown the greatest promise - film digitization, an image intensifier - based system, photostimulable phosphor plates, and a scanned projection system. The physical aspects of each of the four systems and the clinical results that have been reported to date, as well as the advantages and disadvantages of each system, are presented.
Humans↗
A circuit modification that improves mammographic phototimer performance.
The typical mammographic phototimer does not track with breast thickness. For four common, relatively new mammographic units, phototimed density decreases markedly as breast thickness increases. This trend is attributed to three factors: beam hardening, film reciprocity law failure (RFL), and photosensor dark or leakage current. The contributions of these three factors were experimentally quantitated for the phototimer of a Senographé 500T mammography unit. For a phototimed 28-kVp nongrid technique, the density varied from 2.0 for a 2.5-cm-thick phantom to 0.3 for one 7.6 cm thick. Of the 1.7 difference in film density, 1.1 was attributed to beam hardening, 0.2 to RFL, and 0.4 to photomultiplier tube dark current. A circuit modification was installed in the phototimer that offsets the photomultiplier dark current and has a nonlinear response to compensate for beam hardening and RFL effects. The modified phototimer tracked to within +/- 0.06 density for a 28-kVp grid technique as phantom thickness was varied from 2.0 to 6.0 cm. Similar results were obtained for nongrid techniques.
Female↗
[Prototype digital unit dedicated to radiography of the thorax].
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Evaluation Studies as Topic↗
Mineral content of bone: measurement by energy subtraction digital chest radiography.
Several methods are presently available for measuring the mineral content of bone. Those in widespread use include dual-photon absorptiometry and quantitative CT. The feasibility of using dual-energy digital chest radiography for determination of the mineral content of posterior ribs on digital chest images was studied by using a prototype unit. The results showed a significant difference in the mineral density of the posterior ribs of control subjects and those of patients who had osteoporosis (251.1 +/- 36 mg Ca2+/cm2 of rib vs 158.8 +/- 48 mg Ca2+/cm2, p less than or equal to .01) and a close correlation with values obtained by dual-photon absorptiometry of the lumbar spine (r = .77). The results suggest that this technique can provide an accurate assessment of the presence or absence of osteoporosis.
Adult↗
Scanned projection digital radiography of the chest. A review of five years' experience.
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Calcinosis↗
Effects of strong government measures against tobacco in Hong Kong.
The government of Hong Kong grasped the political nettle of control of tobacco in the early 1980s, since when a comprehensive policy of legislation, education, and publicity, together with large increases in taxation on tobacco products, has been introduced. This has led to almost all of the population of Hong Kong having knowledge of the harmful effects of tobacco and of antismoking measures taken by the government. From 1982 to 1984 the number of people who smoked daily fell appreciably from 888 300 to 744 500, a reduction of 16%, while the number of teenage smokers was halved (from 22 600 to 11 200). Government commitment is crucial in programmes against tobacco in developing countries; without it antismoking efforts are unlikely to be successful.
Adolescent↗
Equilibrium penetration of monolayers IV: dipalmitoyllecithin-centrimonium bromide system.
Equilibrium surface pressure-area isotherms of dipalmitoyllecithin monolayers were measured on substrates containing various concentrations of the surfactant, cetrimonium (hexadecyltrimethylammonium) bromide. From these isotherms, the saturation adsorptions of surfactant for various surface lecithin concentrations were calculated. Plotting of these adsorptions against the inverse of the area per lecithin molecule, as required for the "accessible area" theory, revealed two linear segments, corresponding to penetrating at high and at low monolayer areas. At both high and low areas, the adsorption into the accessible areas of the surface was similar to adsorption at a monolayer-free surface. The effective cross-sectional area of the monolayer molecule in the low area region was equal to the collapse area; in the high area region, it was equal to an area corresponding to the co-area, as calculated from the Amagat equation. The change in cross-sectional area corresponded to the transition in the monolayer from a liquid condensed state to a liquid expanded state.
Adsorption↗
Equilibrium penetration of monolayers VI: cholesterol-cetrimonium bromide system.
Equilibrium surface pressure-area isotherms for the penetration of cholesterol monolayers by the surfactant cetrimonium bromide are presented. From these isotherms, the saturation adsorptions of surfactant for various surface concentrations of cholesterol were calculated. Plots of adsorption against the inverse of the area per cholesterol molecule revealed two linear revealed two linear regions, corresponding to penetration at high and low monolayer areas. At high monolayer areas, surfactant adsorption into accessible areas of the surface was similar to adsorption at a monolayer-free surface. In this region, packing of cholesterol and surfactant molecules on the surface lowered the effective cross-sectional area of the cholesterol molecule. However, at low monolayer areas, adsorption was determined by the size of the surfactant ion and the effective area of the cholesterol molecule was equal to the collapse area of a pure cholesterol monolayer.
Adsorption↗
The intensity of scattered radiation in mammography.
The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations. The relative intensity of scattered radiation measured was essentially independent of kVp but increased as the phantom thickness and radiation field size increased. For the range of field sizes and phantom thicknesses that typify clinical situations the intensity of scattered radiation varied from about 40 to 85% of the primary beam intensity indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.
Mammography↗
Scanning multiple slit assembly: a practical and efficient device to reduce scatter.
A scanning multiple slit assembly consisting of an array of long narrow beam-defining slits coupled with scatter-eliminating slots beneath the patient is a feasible, practical, and efficient method of reducing scatter and increasing contrast and image quality in diagnostic radiology. Measurements of the ratio of scattered-to-primary radiation transmitted by a scanning multiple slit assembly and a conventional high ratio grid under similar conditions showed the relative intensity of scatter transmitted by the slit assembly to be only one-third that of the grid. A noticeable improvement in contrast was obtained using the slit assembly, without increase in patient exposure. The design, construction, and clinical implications of such a scatter-eliminating technique are discussed.
Humans↗
Reduction of scatter in diagnostic radiology by means of a scanning multiple slit assembly.
Evidence is presented that an array of long, narrow beam-defining slits scanning a patient coupled with scatter-eliminating slots beneath the patient will substantially reduce scatter in diagnostic radiology. Scatter/primary ratios and the distribution of scatter in the plane of the image detector have been measured as a function of slit width and slot depth for a long, narrow beam-defining geometry. Using these data, calculations for the scatter/primary ratio incident on the image detector are made for a multiple slit assembly and compared with conventional grids. An improvement in contrast is obtained with little or no increase in patient exposure. Design considerations for the construction of such an array and data trends are discussed.
Humans↗