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A G Haus

Publications and source records attributed to A G Haus.

At least 19 recordsLinked to original sources
PubMed1997

Processor quality control in laser imaging systems.

Sensitometric techniques for performing processor quality control in laser imaging systems are analyzed in this study. The sensitivity of conventional x-ray films using simulated screen-light sensitometry is compared with helium-neon (HeNe) laser film exposed with a simulated red-light sensitometer, a standalone (reference) laser sensitometer, an experimental (unstable) laser sensitometer, and laser printers. Infrared (IR) laser film exposed with an IR laser diode and a simulated IR sensitometer are also evaluated. It is demonstrated that laser-generated step tablets provide an easy and reliable method of performing laser film processor quality control.

Helium↗
PubMed1997

Evaluation of a cassette-screen-film combination for radiation therapy portal localization imaging with improved contrast.

A traditional limitation with radiation therapy portal images is low image contrast, due in part to the low attenuation of the exposing radiation by the tissues being imaged, and the contrast capabilities of the image receptor. We have developed, and have clinically evaluated, a cassette-screen-film combination for portal localization imaging, which features a copper front screen plus Gd2O2S:Tb fluorescent screens and a slow-speed, fine grain, film emulsion with inherently high contrast coated on both sides of a 7 mil Estar base. The film can be processed in a conventional rapid-process film processor. Sensitometric data indicate that the film contrast (average gradient) for the new combination is approximately 3.5 times higher than the conventional portal localization systems in current use. The new combination has been clinically compared with two conventional systems. The required monitor unit settings were found to be similar. Initial clinical results indicate portal images made with the new combination are superior to those obtained with the conventional combinations. The images have much higher contrast, subjective impressions of lower noise, show clearer definition of structures, and are much easier to read.

Biophysical Phenomena↗
PubMed1997

Effects of ambient light and view box luminance on the detection of calcifications in mammography.

OBJECTIVE: Viewing conditions can affect diagnostic performance differently depending on background optical densities. We quantified detection accuracy when viewing calcifications in glandular tissue under recommended viewing conditions versus accuracy with lower view box luminance and higher ambient lighting. MATERIALS AND METHODS: A phantom with adipose, 50% adipose and 50% glandular, and glandular-simulating material was imaged, and images were interpreted by five medical imaging physicists using two lighting conditions: the recommended one, high view box luminance (4365 nits) with low ambient light (25 lx), and a suboptimal one, low view box luminance (1763 nits) with moderate ambient lighting (290 lx). Then, a dense (Breast Imaging Reporting and Data System breast composition pattern type 4) unfixed cadaveric breast with numerous native calcifications was imaged 28 times. Nineteen of the films had added clusters of simulated calcifications. Three radiology fellows, each with 11 months of training in mammography, identified the added calcification clusters in the images under the two lighting conditions. Changes in phantom analysis and accuracy of the clinical diagnosis were compared for each lighting condition. RESULTS: On mammograms of the phantom, both speck and fibril identification were degraded by an average of 1.4 objects for the adipose-simulating section (with its darker optical density). For medium optical densities, found in the section with the simulation of 50% glandular and 50% adipose tissue, suboptimal lighting conditions had little or no effect on speck and fibril identification. For sections of the phantom that simulated glandular tissue, an average of 0.6 specks or fibers were not seen when lighting was suboptimal. With the dense cadaveric breast, the fraction of added calcification clusters detected by the three observers improved by an average of 17% when low luminance viewers and high ambient light were replaced with recommended viewing conditions; individual scores of the observers improved significantly: p values ranged from .02 to .05. CONCLUSION: Luminance of the view box and ambient lighting significantly affect detection of calcifications in dense breasts when images are interpreted by radiologists with about 1 year of training in mammography. Detection of calcifications in phantoms is primarily degraded for adipose tissue with its darker optical density. However, when lighting conditions are suboptimal, some observers also have trouble detecting calcifications in glandular tissue with its low optical density.

Adipose Tissue↗
PubMed1996

The AAPM/RSNA physics tutorial for residents. Measures of screen-film performance.

The choice of screen-film combination, combined with film-processing conditions, substantially affects radiographic image quality (contrast, blur, and noise) and radiation dose. Film type (single or double emulsion, silver halide content, grain morphology, and spectral sensitivity), processing conditions (chemicals, temperature, time, and agitation), fog level (storage, safelight, light leaks), and characteristics (gradient) determine how the x-ray intensity pattern will be related to the optical density pattern in the radiograph. The type of screen (phosphor layer thickness, light-absorbing dyes and pigments, phosphor particle size), speed of the screen-film processing system (sensitivity), film granularity, screen uniformity, and film contrast affect radiographic noise. Detective quantum efficiency is the basic measure of the efficiency of an imaging system and takes into account the contrast, image blur, speed, and image noise of the system. For radiologists, residents, medical physicists, and technologists involved in medical imaging, it is important to have a basic understanding of the characteristics of screen-film and film-processing systems.

Humans↗
PubMed1995

Physicists in mammography--a historical perspective.

Medical physicists and engineers, working with radiologists and technologists, have made significant contributions in the design of mammographic x-ray units and image receptors, as well as in the development of methods for evaluating mammographic image quality and procedures for quality control. More accurate methods of measuring radiation exposure in the energy range of mammography and more relevant calculations of radiation dose to breast tissue at risk have also been realized. This article will discuss some of the major contributions made by medical physicists for the benefit of mammography. Contributions of radiologists in mammography have been published elsewhere [Bassett, Gold, and Kimme-Smith (1994)]. All contributions cited in this article are based on referenced publications and citations in the following: Medical Physics; Radiology; NCRP Report No. 85; Quality Determinants in Mammography; AAPM Report No. 29; Reduced Dose Mammography, W. W. Logan and E. P. Muntz (editors); RSNA Categorical Course: Technical Aspects of Breast Imaging, A. Haus and M. Yaffe (editors); Film Processing in Medical Imaging, A. G. Haus (editor); Screen-Film Mammography: Imaging Considerations in Medical Physics, G. T. Barnes and G. Donald Frey (editors). The article is divided into six sections: (1) x-ray equipment and receptor development, (2) image quality, (3) radiation dose, (4) phantoms, (5) quality assurance, (6) digital mammography, and (7) reports and committees.

Biophysics↗
PubMed1994

Method of simulated screen sensitometry for asymmetric, low crossover medical x-ray films.

Recognition of the importance of performing simulated screen-light sensitometry of medical x-ray films for the purpose of processor quality control has increased over the past several years. As a result there is a greater need to provide new techniques for performing simulated screen-light sensitometry. Medical films with reduced intensifying screen-light crossover intended to achieve reduced blur and higher spatial resolution pose particular problems in doing simulated screen-light sensitometry if care is not taken to choose a proper simulated light sensitometer with the capability of simultaneous double-sided exposures. Misleading and incorrect sensitometric data can be obtained for film contrast evaluation if a single side exposure is used. Asymmetric, near-zero crossover films pose even greater problems as proper orientation of the film and proper degree of light output asymmetry need be achieved in order to obtain correct sensitometry. The films used in this study were three double emulsion films varying in crossover from 3% to 24%. Of the two very-low-crossover films, one had symmetric emulsion layers while the second featured emulsion layers which were asymmetric in terms of contrast and speed. Sensitometric data show several curve shapes with significant distortions, depending on orientation, for the asymmetric, low-crossover film when exposed using a single-sided exposure. Only by using a double-sided exposure and an appropriate neutral density filter to simulate the degree of screen-light asymmetry in this system could one achieve a characteristic curve comparable to that achieved by inverse square sensitometry.

Biophysical Phenomena↗
PubMed1993

Technological improvements in mammography over the past 20 years.

During the past twenty years many significant technological improvements in mammographic X-ray equipment and screen-film-processing systems have occurred. Today it is possible to obtain mammograms with higher image quality at a significantly lower radiation dose compared to mammograms dating back about 20 years. In this review article, X-ray spectra, limiting geometric resolution, characteristic (H & D) curves, modulation transfer function (MTF) and noise power spectra (NPS) are used to demonstrate technological improvements in mammographic screen-film image quality.

Female↗
PubMed1990

Technologic improvements in screen-film mammography.

During the past 20 years, many significant technologic improvements in mammographic x-ray equipment and screen-film-processing systems have occurred. Today it is possible to obtain mammograms with higher image quality at a significantly lower radiation dose, compared with mammograms dating back about 20 years. In this review article, clinical image comparisons and technical information--including x-ray spectra, limiting geometric resolution, sensitometric characteristic curves, modulation transfer function, and noise power spectra--are used to demonstrate technologic improvements in mammographic image quality.

Female↗
PubMed1989

Screen film processing systems for medical radiography: a historical review.

Since Roentgen first experimented with radiation to produce a radiographic image, many milestones have been reached in the design and manufacture of intensifying screens, medical x-ray films, film processors and chemicals. As a result, high-quality medical radiographs are obtainable today at very low radiation dose. This progress is the result of major contributions and the collaborative efforts of many individuals in industries, universities, and medical institutions involved in basic research, development and manufacturing. This article highlights some of the major advances in the evolution of screen-film-processor chemical systems for medical radiography. Photographs, radiographs, and scientific data are included which illustrate some of the major achievements.

Europe↗
PubMed1989

Processing of mammographic films: technical and clinical considerations.

Sensitometrically exposed film strips and clinical mammograms from single-emulsion Kodak Ortho M SO-177 and double-emulsion Kodak T-Mat M II films were processed in separate film processors set up for standard and extended-cycle processing. For the extended-cycle method, it is necessary to use a process that is dedicated to mammographic films only. Radiation dose reductions of approximately 30% for Ortho M film and 13% for T-Mat M II film were achieved with the extended-cycle process. In the mammogram comparisons, higher-contrast images were obtained with Ortho M film in the extended-cycle process, which allowed for improved demonstration of marginal structural characteristics of soft-tissue masses and better differentiation of benign and malignant tumors. No significant differences in contrast were observed in the T-Mat M II mammograms obtained with the extended-cycle process.

Adult↗
PubMed1987

Recent advances in screen-film mammography.

Today there are many dedicated mammographic x-ray units available that are capable of providing high-quality screen-film mammograms. Likewise, screen-film combinations designed for mammography are capable of providing images with appropriate contrast, resolution, and noise levels. Proper film processing is most important in order to obtain the appropriate film speed and contrast. A higher-speed screen-film combination designed for mammography can provide mammograms with significantly lower radiation dose, especially for grid and magnification techniques. Designing x-ray units and techniques as well as screen-film combinations with the singular goal of reducing radiation dose will always involve compromises and trade-offs. The key is to always consider optimizing all of the factors that affect image quality: (1) appropriate beam quality, (2) breast compression, (3) consideration of the use of grids, (4) good geometry, (5) selection of an appropriate screen-film combination, and (6) proper film processing. Optimization of all appropriate imaging factors will produce high-quality mammograms at the lowest radiation dose to the patient.

Female↗
PubMed1980

Effects of geometric and screen-film unsharpness in conventional and 350-kVp chest radiography.

Clinical comparison of 350- and conventional 120-kVp techniques indicates that small linear structures, such as small pulmonary blood vessels, are shown better at 120 kVp, due in part to two factors affecting image unsharpness: geometric and screen-film unsharpness. The combined effects of geometric (Ug) and screen-film unsharpness were evaluated for both kVp levels. The total-system modulation transfer function (MTFUg X MTFscreen-film) demonstrates differences in unsharpness under two conditions: (a) when the same screen-film system is used with different magnifications (i.e., extreme planes in the chest) and (b) when different screen-film systems are used for magnification of the midplane of the chest.

Humans↗
PubMed1979

Magnification mammography: evaluation of screen-film and xeroradiographic techniques.

An x-ray unit designed for conventional nonmagnification and magnification mammography has been evaluated in terms of image quality and corresponding radiation exposure levels. The technical advantages of the radiographic magnification technique can result in improved image quality and reduction of the recording-system noise. The microfocal spot allows 1.5 x magnification mammograms with minimal geometric unsharpness. However, the magnification technique requires an increased radiation dose to the breast, compared to conventional nonmagnification techniques. An additional radiation dose may be required for screen-film magnification views because of reciprocity law failure due to long exposure times. The increased-dose limitation and the small dimensions of the recording-system cassettes have precluded the use of magnification in place of nonmagnified images for routine mammographic examination. The magnification technique has proved to be beneficial in selected cases.

Female↗
PubMed1978

A method of evaluating and minimizing geometric unsharpness for mammographic X-ray units.

A method for measuring and minimizing the effects of geometric unsharpness in mammography involves using a star resolution pattern to determine the equivalent focal spot size of mammographic x-ray units. With this measurement, the limit of resolution at any plane within the breast and the focal spot-to-object distance necessary to obtain the desired limit of resolution are determined. Six mammographic x-ray units were evaluated with this technique. Results show that the resolution capability of four of these units is limited by geometric unsharpness, such that the resolution capability of present mammographic recording systems is not fully utilized.

Mammography↗