The UK and European protocols for mammographic dosimetry use conversion factors that relate incident air kerma to the mean glandular dose (MGD) within the breast. The conversion factors currently used were obtained by computer simulation of a model breast with a composition of 50% adipose and 50% glandular tissues by weight (50% glandularity). Relative conversion factors have been calculated which allow the extension of the protocols to breasts of varying glandularity and for a wider range of mammographic x-ray spectra. The data have also been extended to breasts of a compressed thickness of 11 cm. To facilitate the calculation of MGD in patient surveys, typical breast glandularities are tabulated for women in the age ranges 40-49 and 50-64 years, and for breasts in the thickness range 2-11 cm. In addition, tables of equivalent thickness of polymethyl methacrylate have been provided to allow the simulation for dosimetric purposes of typical breasts of various thicknesses.

The UK National Health Service Breast Screening Programme is currently organized to routinely screen women between the ages of 50 and 64, with screening for older women available on request. The lower end of this age range closely matches the median age for the menopause (51 years), during which significant changes in the composition of the breast are known to occur. In order to quantify the dosimetric effect of these changes, radiographic factors and compressed breast thickness data for a cohort of 1258 women aged between 35 and 79 undergoing breast screening mammography have been used to derive estimates of breast glandularity and mean glandular dose (MGD), and examine their variation with age. The variation of mean radiographic exposure factors with age is also investigated. The presence of a significant number of age trial women within the cohort allowed an extended age range to be studied. Estimates of MGD including corrections for breast glandularity based on compressed breast thickness only, compressed breast thickness and age and for each individual woman are compared with the MGD based on the conventional assumption of a 50:50 adipose/glandular composition. It has been found that the use of the conventional 50:50 assumption leads to overestimates of MGD of up to 13% over the age range considered. By using compressed breast thickness to estimate breast glandularity, this error range can be reduced to 8%, whilst age and compressed breast thickness based glandularity estimates result in an error range of 1%.

This paper explores the application to mammography of phase contrast produced by variations in x-ray refractive index. As a spatially coherent x-ray beam propagates through an x-ray transparent medium, the phase of the incident wavefront becomes modified in a manner related to the electron density of the medium. The resulting phase gradient across the wavefront is equivalent to a small change in direction of the propagation of the wave. For a general object, the change in propagation direction will vary from point to point depending on the structures within the object. The net effect can be recorded in a radiographic image using an appropriate geometry to produce the visual appearance of edge enhancement at interfaces between materials with differing x-ray refractive indices. Normally these materials will also have differences in attenuation coefficient, so the overall effect is to increase the visibility of interfaces between materials. It is proposed that mammographic images can be subtly enhanced by the use of phase contrast information to overcome some of the known limitations of the imaging process whilst leaving the gross radiological appearance of the images substantially unchanged. The design trade-offs required to utilize phase contrast information were investigated using a conventional mammographic x-ray generator and film-screen system. The Leeds TORMAM mammographic image quality test object was then used to demonstrate a considerable improvement in image quality for the phase contrast enhanced images over those produced in the conventional geometry with no increase in radiation dose to the patient. The results are discussed in terms of their possible practical application.

Following the release of European Directive EU 97/43, radiodiagnostic facilities within the European Union are required to implement a system of patient dose reviews based on comparisons with European, national and local diagnostic reference levels (DRLs). Establishing these levels for typical interventional radiology examinations presents a problem as definition of 'typical' examinations can be difficult, patient numbers are limited and these procedures are often performed at a few specialist centres. This paper uses dose-area product (DAP) gathered over a period of 3 years from 40 fluoroscopy rooms to investigate potential difficulties when it comes to forming diagnostic reference levels for interventional radiology. Comparison of DAP distributions with standard complex (fluoroscopy based) examinations such as barium enema reveals considerably more variation for interventional procedures. Two methods of forming a DRL are compared: pooled patient DAP distributions versus a distribution of DAP per room. The bootstrap resampling method is then applied to DAP distributions to form a confidence interval for the chosen DRL statistic. Potential error on a DRL formed at a local level from a limited number of patient dose readings and x-ray rooms is significant. The results are reviewed in the wider context of DRLs in general radiology. For complex examinations, it is suggested that the function of the DRL is best served by setting DRLs based on pooled size-corrected patient DAP distributions rather than distributions of average DAP per room.

A digital subtraction imaging technique was used to visualise directly the anatomical distribution of 3 x 60 ml aliquots of saline containing a low concentration of radio-opaque dye, introduced sequentially into a segment of the middle lobe. It was possible to estimate the relative movement of fluid within the segment during the sequential aspiration of each of these aliquots. The first 60 ml aliquot introduced stayed close to the bronchoscope and probably sampled only the proximal airways. With the introduction of cumulative volumes of 120 ml or more, the fluid filled the segment more evenly. Aspiration then moved fluid back from the periphery, implying that the aspirate had also lavaged both distal airways and alveoli.Bronchoalveolar lavage has become increasingly popular as a diagnostic and research tool over the last 15 years. Its applications have been as diverse as the measurement of mediators after antigen challenge in asthmatic patients' and the diagnosis of Pneumocystis carinii infection in immunosuppressed patients,2 although it is most widely used in the assessment and diagnosis of interstitial lung disease.3 The anatomical distribution of fluid introduced during bronchoalveolar lavage, however, has never been thoroughly investigated and there is wide variation in the way the procedure is performed. The volume instilled by different operators has ranged from 204 to 3005 ml and the site of lavage has varied from first order bronchi6 to subsegmental bronchi.7 In this study we have attempted to define the fluid distribution occurring during a standard bronchoalveolar lavage protocol, as routinely used in our practice, and to assess the movement of fluid that occurs at aspiration. muscularly 30 minutes before bronchoscopy, and 10 mg of diazepam was injected intravenously immediately before the start of the procedure. Over 15 minutes 4ml of 2% lignocaine were administered by nebuliser (Porta-Neb, Medic-aid) and I ml was injected into the trachea via the cricoid membrane, which allowed the procedures to be completed with no more than 2 ml of additional local anaesthetic. Peroral bronchoscopy was then performed with the subject supine and the instrument was wedged into a segment of the middle lobe. The medial segment was chosen for lavage in the first subject (study 1) and the lateral segment in the second (study 2). Both studies were recorded with a computer linked digital radiography system (Picker DAS 21 1), which exposed each subject to a total of 15 chest radiographs. A baseline image of the right hemithorax was taken in the anteroposterior plane at functional residual capacity (FRC) at the beginning of each study for subtraction from subsequent images. This allowed better low contrast sensitivity. Three successive aliquots of sterile phosphate buffered saline containing a 5% solution of the radioopaque iodinated dye lopamidol (Merck) were introduced at 25°C. This dye concentration was selected as a result of a preliminary series of experiments in which test tubes containing 1%, 5%, and 10% iop...