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Microcalcification in a dense breast. a. Contact mammogram, mediolateral projection. Calcifications can be seen behind the nipple (arrowheads).
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The authors describe a new reduce-dose magnification mammography system which uses a microfocal-spot/tungsten-target x-ray tube in conjunction with a high-speed, rare-earth film/screen system. Physical measurements of imaging parametes, phantom tests, and limited clinical trials are reported. Although this system is not yet ready for general use, p...
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Mammographic studies are performed for both diagnosis of breast disease and screening for cancer. Diagnostic mammography can demonstrate the presence of breast cancer in a symptomatic patient and more specifically, the size, location and extent of tumor. Mammographic screening involves examination of asymptomatic women in an attempt to detect breast cancer before it grows large enough to be palpable. The use of diagnostic mammography is well accepted due to the compelling clinical need for the information provided. The implementation of a mammographic screening program depends upon: (1) indication of a favorable benefit/risk ratio for the population being screened; (2) availability of suitably trained radiologists, medical physicists, and technologists and appropriate mammographic equipment subject to a vigorous QA program; and (3) acceptably low cost. Breast anatomy and function must be understood (Section 2) in order to design and utilize the mammographie techniques which will effectively detect and demonstrate breast cancer. The technique which is employed for the preponderance of mammography examinations is screen-film mammography with a grid. Good screen-film mammography requires dedicated equipment which can provide an appropriate soft x-ray beam (proper choice of operating potential, target, filter, window, HVL) (Section 3), proper compression, a target-film distance of suitable length for the given focal-spot size, and provision for vertical adjustment and mechanical rotation of the tube and image-receptor assembly for proper positioning (Section 2). The two views, which are recommended, are the CC and the MLO view (Section 2) which allow more visualization of the posterior glandular tissues, particularly in the auxiliary tail than a lateral view. The lateral view should also be employed whenever a nonpalpable lesion is discovered, in order to provide accurate three-dimensional localization. Screen-film mammography should be performed by a technologist who has had special training in compression and positioning techniques for the standard and special views used for mammography (ACR, 1999). Only an intensifying screen designed specifically for mammography should be used in combination with a suitable single-emulsion film (Section 3). The combination should be placed in low-absorption cassettes designed for mammography. There are many factors which affect image quality (Section 4). The three major components of image quality are contrast, sharpness and noise. Image quality can be optimized by suitable adjustment of the x-ray spectrum (operating potential, filtration, target material), breast compression, grids, imaging geometry (small focal spot, long target-film distance), choice of screens and films, and optimization of film-processing techniques. Image quality may be checked with suitable phantoms. Section 4 provides information to allow facilities to determine whether the particular combination of x-ray machine, compression devices, technique factors and image receptors in current use, or under consideration for use, for mammography will provide optimum image quality. A major objective of mammography dosimetry is to provide relevant information so that potential radiation risks from alternative techniques may be compared. For this purpose a single-valued "dose" per view for each technique, which corresponds reasonably well to the resulting carcinogenic potential, should be determined. This task involves consideration of tissue vulnerability to radiation effects, anatomy, technique and dosimetry. In addition, a unique dose value for each technique requires that the dose be determined for a fixed-reference breast composition with breast thickness stated. Simple computational models of the breast have been developed for estimation of mammographic dose. Several assumptions are implicit in these models relating to radiation risk, breast anatomy, and technique (Section 5). Three specific points are relevant to radiation risk: (1) breast glandular tissue is most vulnerable as compared with adipose, skin and areolar tissues; (2) an average breast dose (namely, the mean glandular dose), rather than a maximum dose, is most useful in characterizing risk of carcinogenesis consistent with a linear dose-response relationship; and (3) the population of primary interest is women 40 y and older since younger women are likely to receive only diagnostic and baseline studies. This assumption that the population of primary interest is women 40 y and older limits application of the computational models to the older on average, more adipose breast, which helps justify certain simplifying assumptions. A major technique variable is the degree of compression employed. Firm compression, which is assumed in dose computations, greatly distorts the breast anatomy, making more rectangular the sagittal and transverse cross-sections of the volume that includes the glandular tissue. This greatly simplifies the breast geometry and makes the computational models more appropriate than otherwise would be the case (Section 5). The mean glandular dose (D̄g) meets the stated requirements outlined above. The computational model used in this Report for D̄g assumes that 0.5 cm thick adipose layers enclose a central "glandular tissue" containing a uniform mix of glandular and adipose tissues in roughly equal amounts. The procedure for estimating mean glandular dose for a specific population of patients is described in Table 4.3 (Approach II). A basic requirement for maintaining optimum image quality in mammography is implementation of a suitable QA program (Section 6). Each of the items contributing to image quality must be evaluated on a regular basis. The quality administration program (medical audit) evaluates the appropriateness and accuracy of image interpretation (Section 6.3). The benefit from screening by mammography and physical examination in the form of decreased breast cancer mortality has long been accepted for women above age 50 on the basis of a randomized trial (the HIP study, see Section 7), which indicated that the contribution of mammography to decreased breast cancer mortality was significant in older women. The randomized clinical trials of mammographic screening have not demonstrated a benefit for women age 40 to 49, within the first 7 y of starting screening. Those trials for which 10 or more years of follow-up is available, show evidence of a 23 percent benefit in reducing mortality. Although this reduction is smaller than that observed for older women, it is statistically significant and therefore, one can reject the possibility that this may have happened by chance. Compared with mammography practiced in the previous randomized trials, high-quality modern mammography could result in increased benefit. Even a very small benefit (e.g., one percent) more than offsets any risk of radiation-induced breast cancer. The benefit versus risk will be substantial, if analysis of ongoing screening experience demonstrates a reduction in breast cancer mortality rate of 30 percent or more. Among the various imaging methods designed to evaluate the breast for cancer, mammography is the most accurate and most widely used. It has gained clinical acceptance primarily because of its ability to detect a cancer before the tumor mass becomes large enough to be palpable, thereby permitting "early" diagnosis. It has also been proven an invaluable tool to distinguish benign from malignant lesions and can facilitate prompt biopsy of cancers, while encouraging clinical observation (rather than biopsy) of many benign masses. Other breast imaging methods have, thus far, been considered less successful; these include thermography, transillumination, ultrasonography, and MRI and MRS all of which do not utilize ionizing radiation. Computed tomography (Section 8.4) and digital mammography (Section 3.3) which use x rays, and therefore involve the potential risk of mammary carcinogenesis are being subjected to clinical investigation to determine their role in breast cancer diagnosis. Explanations of the principles of operation, a chronology of developments, and an extensive discussion of the limitations of each of these methods is contained in Sections 3.3 and 8.4.
The aim of our study was to evaluate a mammography unit capable of magnification of up to fourfold at an equivalent or lower dose than with current systems. A prototype mammography tube with an electron-beam-focusing technology resulting in a focal spot size of 40-120 micro m was combined with a highly intensifying screen-film system. To evaluate contrast-detail resolution, phantom radiographs were performed with the prototype magnification mammography system using a magnification factor of 1.7 for survey views and a magnification factor of 4.0 for spot views. They were compared with unmagnified survey views and magnification spot views (magnification factor 1.9) of a state-of-the-art mammography system. The radiation exposure was measured and mean glandular doses were calculated. The contrast-detail resolution with both prototype (m = 1.7) and conventional (m = 1.1) survey views was equivalent while the entrance dose and the mean glandular dose were approximately 50 % lower with the prototype. For spot views, the contrast-detail resolution was substantially higher for the prototype than for conventional magnification while the dose was equivalent. Dose reduction and improved detail resolution are possible with this new technology.
Special imaging problems arise in mammography since the conditions are quite different from those in other fields of radiology. The differences in attenuation of the various soft tissue structures in the female breast are small, and it is necessary to use X-rays with low photon energy in order to get a sufficiently high contrast in the mammographic film. Jennings and Fewell (1979) examined the relative exposure necessary to achieve a constant signal-to-noise ratio for various photon energies. They found a minimum at approximately 20 keV, when glandular tissue in the breast was imaged. Moreover, small details such as microcalcifications may have diameters no larger than 0.1 mm and can only be imaged using a system with high spatial resolution. Although microcalcifications have high attenuation, their small dimensions along the direction of the X-ray beam reduce their attenuation so that it is necessary to use a system giving high contrast.
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.
Magnification mammography is an adjunct to conventional mammographic technique. It produces fine-detail breast images containing additional anatomic information that may prove useful in refining mammographic diagnosis, especially in cases where conventional imaging demonstrates uncertain or equivocal findings.
Some of the parameters determining image quality in mammography are analyzed: the effects of primary photon spectra, focal spot size and screen-film systems on spatial resolution are discussed as are scattered radiation, development temperature and absorbed dose. The parameters limiting spatial resolution and contrast are evaluated for the standard and magnification techniques. Methods of reducing scattered radiation to improve contrast are evaluated. Scatter to primary ratios for different scatter reducing methods are compared, using the physical quantity energy imparted. For the standard technique the spatial resolution has been found to be limited by the fluorescent screen. With magnification technique the focal spot is the weakest link for the spatial resolution. The contrast is mainly set by the amount of scatter using the standard technique considering the use of a low tube potential (approximately 25 kVp). Using the magnification technique the amount of scatter is so small, that the tube potential is the limiting factor. We have found the optimized standard mammographic technique to be achieved under the following conditions: 25 kVp, 0.3 to 0.6 mm focal spot, film-focus distance 500 mm, anti-scatter grid, developing temperature 36 to 38 degrees C and 4 minutes total processing time with the screen-film system we have used. In magnification technique an air gap of at least 20 mm is desired. With an FFD of about 500 mm this will give a magnification ratio of 1.8 to 2.0 and a 0.1 mm X 0.1 mm focus spot is mandatory. With this technique, it is necessary to use a faster screen-film system than that used in standard mammography.
The application of nonionizing radiations and magnetism in clinical medical diagnosis has been rapidly increasing. The incorporation of these techniques into the armamentarium of the diagnostic roentgenologist warrants a change in nonmenclature to diagnostic imageologists. This review of the clinical applications of diaphanography covers the period of simple light source examination of the 1930s to the present sophisticated imaging with infrared film or videcon T.V. computerized format. Light physics of the infrared spectrum is well known, however experimental data of the mechanism of transillumination or normal and abnormal breasts are being investigated. A short discussion of breast anatomy and pathology including benign and malignant is basic to the clinical evaluation technique. A realistic appraisal of the application, the limitations of the technique and the current ongoing investigative studies in the European and American literatures are reviewed. Other noninvasive breast diagnostic techniques of thermography, ultrasound, and NMR are included as well as mammography in the diagnosis of breast disease and cancer.
This article reviews milestones in the technological development of mammography since 1970. Mammography is particularly underutilized as a screening procedure for breast cancer and the reasons for its continued inappropriate and under use are explored. Although there are some known barriers to increased utilization among the female adult population, the majority of barriers reside within the domain of referring physicians. Remedies to address the low referral rates for screening mammography are outlined for federal agencies, radiology groups, mammography equipment companies, medical schools, and philanthropic groups. Until the developers of technological procedures such as mammography appreciate that the application of a technology and its appropriate utilization by professionals and the public are important to consider when the technology is developed, utilization rates may not do justice to the technology's potential.
