Search PubMed⌕ Search

Biomedical subjects

G T Barnes

Publications and source records attributed to G T Barnes.

At least 37 records · Page 2Linked to original sources
PubMed1994

Mouse Huntington's disease gene homolog (Hdh).

The incurable neurodegenerative disorder, Huntington's disease (HD), is caused by an expanded, unstable CAG repeat encoding a stretch of polyglutamine in a 4p16.3 gene (HD) of unknown function. Near the CAG repeat is a polyproline-encoding CCG repeat that shows more limited allelic variation. The mouse homologue, Hdh, has been mapped to chromosome 5, in a region devoid of mutations causing any comparable phenotype. We have isolated overlapping cDNAs from the Hdh gene and compared their sequences with the human transcript. The consensus mouse coding sequence is 86% identical to the human at the DNA level and 91% identical at the protein level. Despite the overall high level of conservation, Hdh possesses an imperfect CAG repeat encoding only seven consecutive glutamines, compared to the 13-36 residues that are normal in man. Although no evidence for polymorphic variation of the CAG repeat was seen, a nearby CCG repeat differed in length by one unit between several strains of laboratory mouse and Mus spretus. The absence of a long CAG repeat in the mouse is consistent with the lack of a spontaneous mouse model of HD. The information presented concerning the sequence of the mouse gene should facilitate attempts to create such a model.

Amino Acid Sequence↗
PubMed1994

Computed radiography: user-programmable features and capabilities.

Digital or computed radiography (CR) using photostimulable storage phosphor plate technology is becoming increasingly popular in certain clinical applications, such as bedside radiography, where it possesses clear advantages over conventional screen-film imaging. The majority of CR systems in clinical use have been manufactured by Fuji Medical Systems USA, Inc (Stamford, CT) and provide a surprising degree of flexibility. Fuji CR units are delivered with preset menus, hardcopy format, and image-processing parameters for each examination. Of practical importance is that users may change the exam menu and printed film format as well as the image-processing parameters for each examination. There is, however, a lack of documentation describing these features and how they are programmed. This paper addresses these issues. Examples are given on how to change: 1) the printed film format, 2) the contrast and gray-scale processing, 3) spatial frequency enhancement, and 4) the appearance of the operator interface menus.

Algorithms↗
PubMed1994

X-ray tube potential, filtration, and detector considerations in dual-energy chest radiography.

The effect of x-ray tube potential and prepatient and interdetector filtration in single exposure dual energy chest imaging has been studied employing a carefully benchmarked model. The analysis utilized published methodology. Noise in simulated lung and mediastinum fields of the aluminum (bone) and Lucite (soft tissue) images were studied at fixed entrance skin exposure (ESE) for commonly employed sandwich detector and sandwich imaging plate configurations. Our results indicate noise in the lung increases slowly with tube potential above 120 kVp, while noise in the mediastinum decreases rapidly. Also, at high tube potential (> or = 120 kVp) adding moderate amounts of prepatient K-edge filtration (approximately equal to 100 mg/cm2) while optimizing imaging conditions for the lung tends to decrease noise in the lungs by approximately equal to 30% while increasing noise in the mediastinum by a similar amount. Without K-edge prepatient filtration, noise in the lung is minimized with Cu interdetector filter weights near 400 mg/cm2. In the mediastinum noise is minimized with heavier interdetector filter and prepatient K-edge filter weights. Prepatient K-edge filter weights that minimize image noise in either field can increase the tube loading by factors ranging from 10 to 10(10). Systems designed with sandwich detectors using commercially available phosphors and coating weights can produce contrast-to-noise ratios (CNRs) as high as 50% of the theoretical limit (defined as an optimized system with a totally absorbing rear detector).

Humans↗
PubMed1994

Mammography accreditation and equipment performance.

Not all sites performing mammography produce optimal images at acceptably low doses. To address this situation, a voluntary accreditation program was instituted through the American College of Radiology. Each site applying for accreditation completes a detailed questionnaire about facilities and equipment, personnel, and quality control. Each unit at each site is evaluated by a medical physicist for clinical and phantom image quality and for average glandular dose. Although a site is accredited for 3 years, the performance of each unit is audited annually. Of 11,162 units for which accreditation was sought, only 5,856 (68%) passed at the first attempt, with another 18% passing after reapplication. The major reason for failure was inadequate clinical images, followed by inadequate phantom images, both inadequate clinical and phantom images, and inadequate quality control records. In a performance audit of 20 new units, an average of 5.8 problems were encountered per unit, the majority of which adversely affected image quality. These results support the requirement of equipment performance audits and raise the question of whether similar problems exist in other areas of medical imaging.

Accreditation↗
PubMed1994

Scanning slit chest radiography: a practical and efficient scatter control design.

PURPOSE: To design a chest radiography unit that eliminates scatter. MATERIALS AND METHODS: A scanning slit radiography unit that also incorporates a conventional grid was designed. The scanning slit geometry defined a 10-mm-wide beam at the image receptor. RESULTS: With a typical heavy-duty radiographic tube, the proposed system was capable of delivering an entrance skin exposure of up to 32 microC/kg for a 1-second scan. Monte Carlo simulations indicated that the scatter-to-primary ratio (S/P) imaged with the scanning slit system alone was 0.125 for a 35 x 43-cm, 23-cm-thick Lucite phantom imaged at 140 kVp. When the system was coupled with 4:1, 8:1, and 12:1 grids, S/P decreased to 0.063, 0.055, and 0.054, respectively. CONCLUSION: A scanning slit system coupled with a conventional grid is a practical and highly efficient method of controlling scatter and will result in minimal soft-tissue and bone measurement errors in dual-energy chest radiography.

Humans↗
PubMed1994

Normalized average glandular dose in molybdenum target-rhodium filter and rhodium target-rhodium filter mammography.

PURPOSE: To determine the normalized glandular dose (DgN) for molybdenum target-rhodium filter (Mo-Rh) and rhodium target-rhodium filter (Rh-Rh) mammography and compare the average glandular doses (Dg) that resulted with a conventional molybdenum target-molybdenum filter (Mo-Mo) source assembly. MATERIALS AND METHODS: X-ray spectra models for Mo-Rh and Rh-Rh were developed and used to calculate DgN values for these target-filter combinations as a function of x-ray tube potential, half-value layer, and breast thickness for three breast compositions. For the average glandular dose comparisons, 50/50 phantoms were imaged for the three target-filter source assemblies at three tube potentials. RESULTS: For the same parameters, DgN values for Mo-Rh and Rh-Rh were higher than for Mo-Mo. At the same voltage, the exposures required to image breast phantoms are substantially lower, and as a result, Dgs are also less with Mo-Rh and Rh-Rh than with Mo-Mo. CONCLUSION: DgN values presented permit practical evaluations of average glandular doses for Mo-Rh and Rh-Rh mammography. At a given potential, dose savings are realized with Mo-Rh and Rh-Rh source assemblies.

Adipose Tissue↗
PubMed1993

infoRAD: computers for clinical practice and education in radiology. Teleradiology: fundamental considerations and clinical applications.

Teleradiology, the practice of radiology from a distance, involves transmission of images between two locations. Radiologists off site can be consulted easily and quickly whenever critical questions arise. Similarly, long-distance, real-time radiologic monitoring of patients is possible. Second opinions can be obtained from specialists in difficult cases. The result is improved and more efficient delivery of patient care. The large number of teleradiology products and features often confuses radiologists who are considering the incorporation of teleradiology into their practices. It is important that practice patterns and needs be evaluated prior to specification and acquisition of a teleradiology system.

Computer Systems↗
PubMed1993

Scatter in computed radiography.

The effects of scatter radiation on images obtained with storage phosphor computed radiography (CR) were evaluated. The scatter degradation factor was extended to account separately for forward scatter and backscatter. Values for the ratios of forward scatter to primary radiation (sf/p) and backscatter to primary radiation (sb/p) were measured for various x-ray tube potentials, phantom thicknesses, and field sizes for CR imaging plates (IPs). Similar measurements were made for a common screen-film system. The sb/p values for the IPs were 0.05-3.80. Standard CR cassettes do not have lead foil behind the IP to control backscatter; the results of this study indicate that such control is needed. The sf/p values were 40%-70% higher in IPs (50%-120% higher when backscatter was included) than those in the conventional screen-film system. This difference is attributed to the differences in the K-absorption edges of barium and gadolinium and the fact that scatter has lower effective energy than the primary beam as they exit the patient.

Diagnosis, Computer-Assisted↗
PubMed1993

Scanning slit mammography.

The importance of scatter in mammography and the performance of conventional mammographic grids are reviewed. Without scatter control image contrast is significantly degraded. Conventional mammography grids improve the situation; however, their performance is limited. As a result for 5 to 8 cm thick breasts, a more ideal method of scatter control could result in a 25 to 45% improvement in contrast over that possible with conventional grids. One such approach is scanning slit mammography. The principles of this approach are presented along with the design and geometrical specifications of a prototype multiple scanning slit unit. The unit has a measured primary transmission of 91% and scatter transmission of 3%. Similarly measured performance values for a commonly used grid are 62% and 19%, respectively. Compared are images of a 6 cm breast phantom obtained with the scanning slit unit and a conventional grid. The scanning slit unit achieved noticeably greater image contrast with 30% less radiation. Also discussed are the limitations and engineering challenges of the technology.

Image Processing, Computer-Assisted↗
PubMed1992

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↗
PubMed1991

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↗
PubMed1991

Technical exhibits.

Explore the source record for details and available documents.

Exhibitions as Topic↗
PubMed1991

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↗
PubMed1989

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↗
PubMed1989

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↗
PubMed1989

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↗
PubMed1988

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↗