Image quality: an educational and scientific problem.
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Humans↗
Biomedical subjects
G T Barnes
Publications and source records attributed to G T Barnes.
Radiographic mottle and patient exposure in mammography.
Radiographic mottle has been analyzed in mammography using a comprehensive theory that takes into account fluctuations in absorbed x-ray energy and in phosphor light-photon yield, as well as film granularity and random variations in phosphor coating. Density fluctuations, signal-to-noise ratios, and quantum-efficiencies are presented for two screen/film systems as functions of density and viewing-aperture size. For sampling apertures of less than 500 micrometers in diameter, film granularity is the dominant source of noise for a Kodak Min-R screen/film system. This implies that quantum mottle can be increased and patient exposure reduced with little or no loss in imaged information. Such is the case for the second combination, a Min-R screen combined with Ortho-M film.
Female↗
A linear tomographic alignment test object.
A simple test object that accurately assesses linear tomographic tube and cassette-movement alignment is described. This device consists of two offset pinholes, one located above and one below the fulcrum plane. The test object is easy to make and can be used during the installation and performance testing of conventional tomographic units.
Humans↗
An investigation and explanation of the fall-off of x-ray tube current during an exposure.
It was observed that the radiation output of x-ray tubes falls off exponentially during an exposure with a time constant of about 120 ms. The equilibrium value is approximately 15% lower than that at the beginning of the exposure. The clinically noticeable consequences are discrepancies in x-ray generator calibration, the loss of the strict mA s (tube current X exposure time) linearity, and, in scanning devices, the possibility of artefact generation. A systematic investigation of the phenomenon revealed that it is caused by the cooling of the cathode due to evaporation of electrons. Theoretical expressions for the magnitude and time constant of the fall-off derived from basic thermodynamics are in good agreement with the observations. A simple mA stabilisation circuit which prevents the fall-off is described.
Technology, Radiologic↗
The scanning grid: a novel and effective bucky movement.
A grid consisting of a focused array of radiopaque strips has been constructed. No interspace material is employed, and, during an exposure, the arrangement moves so that the grid strips remain focused and a uniform film density is obtained. Preliminary measurements and radiographs of patients indicate that such a device is a practical and effective method of suppressing scatter.
Humans↗
Kilovoltage bootstrap sensitometry.
A new method for determining the sensitometric curve of radiographic film/screen combinations is described. The approach employs kVp variation at several mAs values to provide the necessary range of exposures. The method is simple and easy to perform and is presented along with experimental data for illustration. The sources and relative magnitude of errors associated with the technique are also discussed.
Technology, Radiologic↗
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↗
The dependence of radiographic mottle on beam quality.
The dependence of radiographic mottle on beam quality has been studied for a variety of film/screen combinations. The measurement technique consisted of scanning the radiographs with a microdenitometer; the analogue signal from the microdesitometer was gated and recorded with a multichannel analyzer. The sampling aperture was 500 mum in diameter and was chosen because its spatial frequency response approximates that of the eye. The standard deviation of the density fluctuations was calculated directly from the number versus density spectrum accumulated in the analyzer. The range of standard deviations' for the various combinations and x-ray tube kilovoltages studied from approximately 0.009 to approximately 0.021 density units. For commonly used combinations, very little kilovoltage dependence was observed. The relative amount varied for different screen phosphors and is attributed to differences in the absorption characteristics.
Humans↗
Film-screen considerations in tomography.
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Humans↗
THE EFFECTS OF SPREADING TECHNIQUE AND PURITY OF SAMPLE ON THE EVAPORATION RESISTANCE OF MONOLAYERS.
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Journal Article↗
Effects of certain electron-microscope stains on phospholipid monolayers.
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Animals↗
A new type of grid.
A new type of grid is discussed. It is anticipated that it will have the same primary transmission as and will eliminate scatter more efficiently than a conventional linear grid of equal thickness and lead content. The construction of the new type of grid is similar to a conventional one except that the lead strips are arranged in zigzag rather than linear pattern. Geometrically ideal "zigzag" and linear grids were constructed and their performance tested. The scatter transmitted by the ideal zigzag grid was one-half that of the comparable ideal linear grid. The implications regarding the improved scatter-eliminating capabilities of a practical zigzag grid are discussed.
Radiography↗
The design and performance of a scanning multiple slit assembly.
A scanning multiple slit assembly (SMSA) has been constructed for the purpose of reducing scatter in medical radiography. The SMSA consists of a series of long, narrow beam-defining slits above the patient that are aligned and synchronously moved with scatter-eliminating slots beneath the patient during an exposure. Evidence, based on measurements of the ratio of scattered-to-primary radiation imaged and radiographs of patients, is presented indicating that such a device is a practical and efficient method of reducing scatter and improving contrast compared to conventional grids. The design considerations and trade-offs associated with the choice of slit width, slit separation distance, and aft slot depth are discussed along with the effect of these parameters on the SMSA's performance. The various problems encountered in obtaining a uniform scan and the manner in which they were handled are also discussed.
Radiography↗
Effect of reduced scatter on radiographic information content and patient exposure: a quantitative demonstration.
If a normal screen-film exposure is made using a conventional grid, a reduced exposure may be used with a superior scatter removal device to record the same image information. This theoretical conclusion is not readily demonstrated because of the limited visibility on the underexposed film. In this study radiographs underexposed by a factor of three with a scanning multiple slit assembly (SMSA) were enhanced autoradiographically and found visually to contain more information than properly exposed radiographs obtained under similar conditions using a conventional Bucky grid. This observation was confirmed by contrast scale and noise measurements. Furthermore, the entrance skin exposure of the radiograph using the SMSA was 45% of that required with the grid technique at the same beam quality.
Radiation Dosage↗