OPTIMIZING TECHNIQUES IN SCREEN-FILM MAMMOGRAPHY - 06/09/11
Résumé |
Improvements in mammography film, film processing, and radiograph equipment have occurred steadily over the last two decades. Changes in film and film processing have led to increased film contrast, with corresponding decreased exposure latitude. This has narrowed the range of radiograph exposures appropriate for screen-film image receptors, placing a higher demand on proper exposure conditions. Improvements in dedicated mammography units have included higher radiation output per unit time; better automatic exposure control (AEC) systems; and a wider choice of target and filtration materials, especially the inclusion of rhodium (Rh) as a target and filtration material providing a higher-energy x-ray beam. This last change has increased the range of technique factors selectable by the user.
In addition, reviews of image quality and technique factors within the American College of Radiology's (ACR) Mammography Accreditation Program indicate that there is considerable room for improvement in the selection of clinical techniques. Despite the fact that compressed breast thicknesses range from under 2 to over 7 cm, some sites still use a single target-filter and a single kilovolt (peak) setting for all breast thicknesses. Other sites use technique factors that incur long exposure times (greater than 2 seconds) even for moderate breast thicknesses. These practices indicate room for improvement in technique factor selection.
Over the last decade, mammography image quality has improved through recognition of the importance of adequate film optical density in mammograms.8, 10, 13, 16 In 1992, Law10 noted that in the UK National Breast Screening Program, approximately 15% of breasts in women 50 to 65 showed a dense structure of area 10 cm2 or greater that was underexposed by conventional mammography. Young et al16 performed a retrospective review of the correlation between the detection rate of small breast cancers (those less than 1 cm in maximum dimension) and average film optical densities at 31 screening centers participating in the UK National Breast Screening Program. They found a wide range of optical densities at participating sites, with an average detection rate for small breast cancers that was significantly higher (1.7±0.1 per 1000) at centers using average optical densities greater than 1.2, compared with an average detection rate of 1.2±0.1 per 1000 for centers using average optical densities less than 1.2. Phantom data have confirmed the effects of optical densities on low-contrast lesion detection.8, 13
Optimizing mammography techniques consists of a series of activities that begin with the choice of mammography film, optimizing film processing for that film type, selection of appropriate technique factors for exposure and proper viewing of mammography films. This article discusses each of these areas. In each area, understanding the basic physics of mammography can assist in optimizing mammography techniques.
Le texte complet de cet article est disponible en PDF.Plan
| Address reprint requests to R. Edward Hendrick, PhD, Lynn Sage Comprehensive Breast Center, Northwestern University Medical School, Galter Pavilion, 13th Floor, 251 East Huron Street, Chicago, IL 60611, e-mail: ehendrick@radiology.nwu.edu |
Vol 38 - N° 4
P. 701-718 - juillet 2000 Retour au numéro
Article précédent
- SUCCESSFUL METHODS TO REDUCE FALSE-POSITIVE MAMMOGRAPHY INTERPRETATIONS
- Edward A. Sickles
- DOUBLE READING
- Daniel B. Kopans
Bienvenue sur EM-consulte, la référence des professionnels de santé.
L’accès au texte intégral de cet article nécessite un abonnement.
Déjà abonné à cette revue ?