[Show abstract][Hide abstract]ABSTRACT: Breast imaging in the UK is currently undergoing a major change, with the widespread implementation of full-field digital mammography (FFDM) equipment. This article looks at some of the advanced imaging techniques that have become possible following the development of FFDM units. These techniques may prove to be useful additions to standard mammography for some groups of women.
Preview · Article · Mar 2010 · The British journal of radiology
[Show abstract][Hide abstract]ABSTRACT: The ability of an observer to detect objects on a radiograph is influenced by the conditions under which the image is viewed. Therefore, to ensure that as much diagnostically relevant information as possible can be extracted from the image, it is important that satisfactory viewing conditions for the task are established and maintained. Factors that are thought to be important are the luminance of the image, glare and ambient light. Together, these factors lead to the formation of reflection on the image, which may degrade the observer's performance. The purpose of this study was to explore, in a systematic manner, the effect of the factors outlined above on the performance of an observer conducting a threshold contrast-detail diameter test. Each factor was investigated separately with attempts made to minimize the confounding effects of other factors. When examined individually, viewing box luminance, ambient light and glare were found to have little effect on the contrast-detail performance of the observers. Reflection was found to have a significant effect, particularly non-uniform reflection, and the magnitude of the effect was related to the contrast degradation factor and reflection modulation. These quantities, which are derived from basic photometric measurements, may be used to develop a protocol to assess viewing conditions in screen-film mammography.
Preview · Article · Apr 2008 · The British journal of radiology
[Show abstract][Hide abstract]ABSTRACT: The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability
to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions
than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing
radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on
an electronic display device are investigated. A test object was used to produce a computed radiography image containing a
wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the
viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing
conditions and the degradation in observer performance related to these quantities. The presence of structured reflection
had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate
viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.
No preview · Article · Feb 2005 · Radiation Protection Dosimetry
[Show abstract][Hide abstract]ABSTRACT: An image restoration approach based on a Bayesian maximum entropy method (MEM) has been applied to a radiological image deconvolution problem, that of reduction of geometric blurring in magnification mammography. The aim of the work is to demonstrate an improvement in image spatial resolution in realistic noisy radiological images with no associated penalty in terms of reduction in the signal-to-noise ratio perceived by the observer. Images of the TORMAM mammographic image quality phantom were recorded using the standard magnification settings of 1.8 magnification/fine focus and also at 1.8 magnification/broad focus and 3.0 magnification/fine focus; the latter two arrangements would normally give rise to unacceptable geometric blurring. Measured point-spread functions were used in conjunction with the MEM image processing to de-blur these images. The results are presented as comparative images of phantom test features and as observer scores for the raw and processed images. Visualization of high resolution features and the total image scores for the test phantom were improved by the application of the MEM processing. It is argued that this successful demonstration of image de-blurring in noisy radiological images offers the possibility of weakening the link between focal spot size and geometric blurring in radiology, thus opening up new approaches to system optimization.
Preview · Article · Dec 2004 · Physics in Medicine and Biology
[Show abstract][Hide abstract]ABSTRACT: The performance of a low dose rate pulsed fluoroscopy option and its successful application to cardiac pacing and electrophysiology is reported. Low dose rate 6.25 frames per second pulsed fluoroscopy was made available in two catheter laboratories at a specialist cardiac centre in February 2003, and was adopted as the standard imaging technique for cardiac pacing procedures. The image quality was found to be considerably poorer than conventional modern units, being very similar to that which would have been accepted as adequate performance 20 years ago, but at less than one-tenth of the dose rate. No problems with the clinical acceptance of this imaging mode for cardiac pacing and electrophysiology have been reported. The already low median patient dose-area product for pacing at this cardiac centre was further reduced by 50% with the introduction of this fluoroscopy option.
No preview · Article · Aug 2004 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: Anomalously high image quality scores were noted for images of the Leeds TORMAM phantom obtained using magnification mammography. Comparison of optical density profiles of fibre features in the images with non-magnified images and images previously obtained using an in-line phase contrast geometry showed the presence of phase contrast enhancement in the magnification images. The effect on the phantom score is particularly marked for this design of phantom owing to its use of fibres, which tend to enhance well. A large proportion of the phantom score is associated with fibrous features. It is concluded that direct comparison of TORMAM phantom scores from magnified images with those from non-magnified images is not valid due to the different balance of physical mechanisms forming the two kinds of image.
No preview · Article · Mar 2002 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: In the National Health Service Breast Screening Programme, regular assessment of the mean glandular doses received by a group of women is recognized as an important part of a quality assurance programme. The use of different tube voltages, to improve the beam penetration for thick or dense breasts, and of X-ray units with programmable exposure modes, requires a large number of measurements to ensure that all the values of tube output and half value layer required for the dose calculations are available. In this work, a computer model is used to produce data that allow the calculation of tube output and half value layer for the range of clinically encountered conditions from measurements routinely obtained during quality assurance tests. The data are given as a series of equations and parameters, enabling the calculations to be easily incorporated into a dose calculation spreadsheet. The results of an experimental verification of the model are presented, showing good agreement between the measured and predicted values of half value layer and tube output for a range of combinations of target, filter and tube voltage.
Preview · Article · May 2001 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: A method of identifying the dose per image when quantum mottle no longer dominates the image statistics is presented as a first step towards quantitative optimization in native and subtracted digital fluorography. The method is based on measurements of threshold contrast over a range of receptor doses and the application of a simple model of the threshold contrast detection task to estimate the magnitude of system noise sources. The point at which system and quantum noise sources are equal in magnitude is proposed as the practical upper limit for dose per image. The method is applied to a typical digital fluorography system and the results are placed into the context of the range of dose per image values found from a regional survey of digital fluorography units. While there is broad agreement between the dose per image values in the survey with values predicted from the experimental method, the considerable spread in survey doses suggests there are instances where the use of a high dose per image is unjustified.
Full-text · Article · May 2001 · Physics in Medicine and Biology
[Show abstract][Hide abstract]ABSTRACT: The magnitude of the observer variations intrinsic to contrast-detail measurements were found to be independent of the type of image used in their determination. The two sources of variation identified, within-observer and between-observer variation, were deduced to be 0.115 and 0.111, respectively (variations expressed as a relative standard deviation). When using the Leeds fluoroscopy test objects, an uncertainty on the measured threshold contrasts of 16% for one observer and 11% for two observers may be anticipated when each observer makes one independent reading. This then implies that a change of one perceived disc on the T010 test object (in which the contrast step between discs is approximately 40%) for one independent measurement made by one observer will be significant within two standard deviations. A further implication is that a more sensitive contrast-detail test object could be developed (with approximately 20% contrast steps between discs), provided that the test object is viewed by two or more observers.
Full-text · Article · Jul 2000 · Physics in Medicine and Biology
[Show abstract][Hide abstract]ABSTRACT: Owing to the high mean film optical densities used in breast screening mammography, and the very high maximum optical densities that can be obtained using modern mammographic film, it is often found that for larger exposures the nominally radio-opaque markers used to identify views, left and right etc., cannot be seen using a normal illuminator. A simple solution to this problem is to back the radio-opaque markers with a thin metal filter chosen to keep the marker information visible over a wide range of exposures. A convenient material for this is copper foil in the form of self-adhesive tape. The improvement in marker contrast produced by this modification is illustrated using point optical density measurements on marked test films produced at the extremes of the mammographic exposure range.
Preview · Article · Sep 1999 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: The requirement to monitor the doses received by patients undergoing diagnostic X-ray examinations is discussed and reviewed in the context of the implementation and coordination of patient dosimetry services within an NHS Region by a regionally managed medical physics department. Four aspects of the dosimetry programme are described. Following installation of dose-area-product (DAP) meters, a region-wide data collection programme and associated database has been established, together with regular dosimetry reports. Thermoluminescence techniques are also widely employed and a complementary automated dosimetry system has been developed. Agreement between calculated and measured doses is generally within 15%. A survey of doses from or scanners in the region has resulted, in some cases, in changes in technique, in order to reduce doses. In mammography, regular assessment of 18 X-ray units has shown that mean glandular doses are consistently less than 2 mGy. An important consideration arising from the entire programme is the need to use the collected dose data to implement changes in technique if dose reduction is indicated or if NRPB reference levels are exceeded. The regionally managed programme ensures that a large database of relevant information, covering a comprehensive range of techniques and equipment, is available to a wide audience of physicists, radiographers and radiologists.
Preview · Article · Dec 1998 · Journal of Radiological Protection
[Show abstract][Hide abstract]ABSTRACT: It has been hypothesized that light-box luminance is an important factor in the detection of objects on radiographs. In this work, existing psychophysical data relating to the measurement of visual thresholds at various scene luminance levels are applied to the problem of the observation of radiographs on a light-box. These data suggest that for a given stimulus size, the threshold contrast varies little over several orders of magnitude of scene luminance. In a series of contrast detail experiments performed over a wide range of light-box luminances it has been demonstrated that the detection of low contrast objects on mammographic film is dominated by external noise, that is noise on the film, rather than the internal visual noise of the observer. It is therefore suggested that in mammography it is inappropriate to base recommendations for optimal values of light-box luminance on psychophysical studies of visual noise. It has been shown that commonly used light-box luminances are suitable for viewing mammograms at the higher average optical densities now being recommended, provided that precautions are taken to avoid glare and reflection.
Preview · Article · Mar 1996 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: The routine assessment of patient dose in the National Health Service Breast Screening Programme is performed as part of the quality assurance protocol recommended by the Institute of Physical Sciences in Medicine. The mean glandular dose to a standard breast is deduced from measurement of the air kerma at the entrance surface of a 4 cm Perspex phantom by applying a series of conversion factors. The exposure factors for this measurement are those used clinically. The measured mean glandular dose is then compared with nationally accepted action levels. In some centres the assessment of mean glandular dose using Perspex is supplemented by patient dose surveys. The mean glandular dose to a series of patients attending a breast screening unit may be estimated from a knowledge of the exposure factors and compressed breast thickness, using a knowledge of the X-ray tube output. Measurements made on units in the Northern Region of England and in Scotland using both methods are presented. The implication of these measurements with regard to patient dose surveys in mammography and quality assurance programmes are discussed. An analysis of the uncertainties associated with the measurement techniques is presented.
Preview · Article · Sep 1995 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: In mammography, it is important that the maximum amount of diagnostic information is obtained from each radiograph. One of the factors influencing image quality is the optical density of the film. In this study, a contrast-detail test object was used to establish the optimum optical density value on the basis of signal-to-noise ratio (SNR) for two mammographic film-screen combinations under particular processing conditions. The optimum optical density, taken as being the point at which the threshold contrast is a minimum varied little with detail size. The optimum optical density for the Fuji film-screen combination with Photosol chemistry was found to be higher than that for the Kodak film-screen combination and Kodak processing conditions studied. Although the actual values of optical density are specific to the fixed processing conditions encountered, the technique has more general applicability.
Preview · Article · Apr 1995 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: A method for obtaining histograms of the frequency of occurrence of optical densities in mammograms has been implemented. Averaged optical density distributions were produced for approximately 50 screening mammograms at each of two centres using different film-screen and processing chemistry combinations. Additional measurements were made on films of two commercially available anthropomorphic breast phantoms. The results show that screening mammograms, on average, exhibit a strongly peaked optical density distribution which corresponds closely to the target optical density measured using the current recommended test protocol for automatic exposure control devices.
No preview · Article · Oct 1994 · British Journal of Radiology
[Show abstract][Hide abstract]ABSTRACT: Data produced by a computer model are presented which allow the amount of molybdenum filtration on a molybdenum target mammographic X-ray set to be estimated from the measurement of the half value layer (HVL) in aluminium. Existing data refer either to tungsten target tubes or to molybdenum target tubes for a single anode angle and a constant potential waveform with the compression plate present. In addition to the tube voltage, the present data take account of the waveform of the tube potential and target angle. The results of an experimental verification of the model are presented and the effect of the geometry used in the experimental set-up discussed. Theoretical predictions of the molybdenum filter thickness made using the data from the model are in good agreement with the measured filter thickness, provided that attention is paid to the experimental geometry.
Preview · Article · May 1992 · British Journal of Radiology