MAMMOGRAPHY

23


MAMMOGRAPHY





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Principles of Mammography



INTRODUCTION AND HISTORICAL DEVELOPMENT


The worldwide incidence of breast cancer is increasing. In the United States, one in eight women who live to age 95 years develops breast cancer sometime during her lifetime. Breast cancer is one of the most common malignancies diagnosed in women; only lung cancer has a greater overall mortality in women. Research has failed to reveal the precise etiology of breast cancer, and only a few major factors, such as family history, are known to increase a woman’s risk of developing the disease. Most women who develop breast cancer have no family history of the disease, however.


Despite its frequency, breast cancer is one of the most treatable cancers. Because this malignancy is most treatable when it is detected early, efforts have been directed toward developing breast cancer screening and early detection methods. Breast cancer mortality rates have declined by 2.3% per year from 1990-2000 in all women, with larger increases in women younger than 50 years of age. This decline is most likely the result of earlier detection and improved treatments.1


Mammography is the most important innovation in breast cancer control since the radical mastectomy was introduced by Halstead in 1898. The primary goal of mammography is to detect breast cancer before it is palpable. The combination of early detection, diagnosis, and treatment has resulted in a steady increase in survival rates. The overall mortality rate for breast cancer has finally decreased for American women.


Before the radical mastectomy was introduced, breast cancer was considered a fatal disease. Less than 5% of patients survived 4 years after diagnosis, and the local recurrence rate for surgically treated breast cancer was greater than 80%. Radical mastectomy increased the 4-year survival rate to 40% and reduced the rate of local recurrence to approximately 10%. No additional improvement in breast cancer survival rates occurred over the next 60 years. Some of the principles of breast cancer management were developed during this time, however, and these remain valid:



Reflecting these principles, the theory of removing all palpable breast masses in hopes of finding earlier cancers was developed, and it was recognized that careful physical examination of the breast could detect some early breast cancers. Most patients with breast cancer still were not diagnosed until their disease was advanced, however. This fact, coupled with the dismal breast cancer survival statistics, highlighted the need for a tool for the early detection of breast cancer. Mammography filled that need (Fig. 23-1).



In 1913, Soloman, a German physician, reported the radiographic appearance of breast cancers. Using radiographic studies of cancerous breasts removed at surgery, he described the mechanism of how breast cancer spread. The first published radiograph of a living person’s breast, made by Kleinschmidt, appeared in a 1927 German medical textbook on malignant tumors. Although publications on mammography appeared in South America, the United States, and Europe during the 1930s, the use of mammography for the diagnosis of breast cancer received little clinical interest. A few pioneers, including LeBorgne in Uruguay, Gershon-Cohen in the United States, and Gros in Germany, published excellent comparisons of mammographic and pathologic anatomy and developed some of the clinical techniques of mammography. At that time, the significance of breast microcalcifications was also well understood.


By the mid-1950s, mammography was considered a reliable clinical tool because of such refinements as low-kilovoltage x-ray tubes with molybdenum targets and high-detail, industrial-grade x-ray film. During this time, Egan in the United States and Gros in Germany popularized the use of mammography for diagnosing and evaluating breast cancer. Breast xerography was introduced in the 1960s and was popularized by Wolfe and Ruzicka. Xerography substantially reduced the radiation dose received by the patient compared with the dose received using industrial-grade x-ray film (Fig. 23-2). Because many physicians found xerographic images easier to understand and evaluate, xeromammography became widely used for evaluating breast disease. The first attempts at widespread population screening began at this time.



The combination of higher resolution, faster speed x-ray film and an intensifying screen was first introduced by the duPont Company. As a result, radiation exposure to the patient was reduced even more. Improved screen-film combinations were developed by Kodak and duPont in 1975. By this time, extremely high-quality mammography images could be produced with very low patient radiation exposures. Since 1975, faster lower dose films, magnification techniques, and grids for scatter reduction have been introduced. It is now known that high-quality mammography, careful physical examination, and monthly breast self-examination (BSE) can result in the detection of breast cancer at an early stage—when it is most curable.


The Breast Cancer Detection Demonstration Project (BCDDP) was implemented in 1973. In this project, 280,000 women underwent annual screening for breast cancer for 5 years at 29 locations throughout the United States. Organized by the American Cancer Society and the National Cancer Institute, this project showed unequivocally that screening, physical examination, mammography, and BSE could provide an early diagnosis. In the BCDDP, more than 41% of all the cancers were found using only mammography, and an even greater proportion of early breast cancers were found only with mammography. The BCDDP was not designed to show that early detection of breast cancer would lead to increased survival rates, but definite evidence from carefully controlled studies in the Netherlands, Sweden, and Germany showed that early diagnosis of breast cancer leads to an increase in curability. In the United States, the Health Insurance Plan study in New York City performed mammography screenings on women older than 50 years and showed the same benefits in reduced mortality rates after early diagnosis of breast cancer.


Mammography must be performed well to be fully effective. In 1992, the Mammography Quality Standards Act (MQSA) was implemented to mandate the maintenance of high-quality breast cancer screening programs. The American College of Radiology (ACR) had been a proponent of high standards in breast imaging since 1967 and implemented an optional Mammography Accreditation Program in 1989. In 1994, mammography became the only radiographic examination to be fully regulated by the federal government. MQSA requires formal training and continuing education for all members of the breast imaging team. In addition, imaging equipment must be inspected regularly, and all quality assurance activities must be documented. Facilities are also required to provide protocols documenting responsibility for communicating mammogram results to the patient and the referring physician, providing follow-up, tracking patients, and monitoring outcomes. The goal of MQSA is for high-quality mammography to be performed by individuals most qualified to do so and by individuals who are willing to accept full responsibility for providing that service with continuity of care.



RISK VERSUS BENEFIT


In the mid-1970s, the media-influenced public perception was that radiation exposure from diagnostic x-rays would induce more breast cancers than would be detected. Although radiation dosage during a mammography examination has decreased dramatically since the 1970s, fear of radiation exposure still causes some women to refuse mammography, and many women who undergo the examination are concerned about exposure levels and the resultant risk of carcinogenesis. To assuage these fears, the radiographer must understand the relationship between breast irradiation and breast cancer and the relative risks of mammography in light of the natural incidence of breast cancer and the potential benefit of the examination. No direct evidence exists to suggest that the small doses of diagnostic x-rays used in mammography can induce breast cancer. It has been shown, however, that large radiation doses can increase the incidence of breast cancer and that the risk is dose-dependent. The evidence to support the increased risk of breast cancer from breast irradiation comes from studies of three groups of women in whom the incidence of breast cancer increased after they were exposed to large doses of radiation: (1) women exposed to the atomic bombs at Hiroshima and Nagasaki, (2) women with tuberculosis who received multiple fluoroscopic examinations of the chest, and (3) women who were treated with radiation for postpartum mastitis. The radiation dose received by these women (600 to 700 rads) was many times higher, however, than the dose received from mammography.


Mean glandular dose provides the best indicator of radiation risk to a patient. In 1997, the average mean glandular dose for a two-projection screen-film-grid mammogram for all facilities in the United States inspected under MQSA was 320 mrad.1 Using that level as a gauge, the lifetime risk of mortality from mammography-induced radiation is 5 deaths per 1 million patients. In other terms, the risk received from having an x-ray mammogram using a screen-film combination is equivalent to smoking several cigarettes, driving 60 miles in an automobile, or being a 60-year-old man for 10 minutes.


Fig. 23-3 shows a chart displaying average values for mean glandular dose and estimates of image quality in mammography for the period from the early 1970s to 2005. Doses in mammography have consistently decreased with time, with the most substantial reductions in dose occurring from the early 1970s to the early 1980s. Image quality data are presented from the mid-1980s to the present and show consistent improvement with time.2



An important observation in the previously mentioned population studies is that the breast tissue of young women in their teenage years to early 20s seems to be much more sensitive to radiation than the breast tissue of women older than 30 years. Because breast irradiation is a concern, radiologic examinations need to be performed with only the radiation dose that is necessary for providing accurate detection.



BREAST CANCER SCREENING


The frequency with which women should undergo screening mammography depends on their age and personal risk of developing breast cancer. The current recommendations from the American Cancer Society and the ACR are that all women older than 40 years should undergo annual mammography and should continue yearly mammography for as long as they are in reasonably good health otherwise. A baseline examination made sometime before the onset of menopause is useful for comparison during subsequent evaluations. High-risk patients should consider beginning screening mammography at an earlier age.


The term screening mammography is applied to a procedure performed on an asymptomatic patient or a patient who presents without any known breast problems. For a procedure to be used as a screening method, it must meet the following criteria:



Mammography is a relatively simple procedure that takes only about 15 minutes to complete. The acceptability of mammography, which is the only radiographic procedure used to screen cancer, has been confirmed in numerous studies. Mammography cannot detect all cancerous lesions, however. An annual clinical breast examination is recommended by the American Cancer Society. Many physicians also recommend that women perform monthly BSEs. Even when mammography is performed properly, approximately 10% of cancers remain radiographically occult, particularly in dense breasts and augmented breasts. Even so, mammography has greater sensitivity and specificity for detecting breast tumors than any other currently available noninvasive diagnostic technique. When compared with magnetic resonance imaging (MRI), ultrasonography, and digital techniques, mammography is more cost-effective and more reproducible when quality control standards are maintained. Mammography must be performed properly to maintain these characteristics, however. As with other imaging modalities, high-quality mammography requires an extremely dedicated staff with the appropriate training and expertise.


Breast cancer screening studies have shown that early detection is essential to reducing mortality and that the most effective approach is to combine clinical breast examination with mammography at directed intervals. Although massive screening efforts initially may seem cost prohibitive, the actual cost of screening in the long-term is much less than the expenses involved in caring for patients with advanced breast disease. To this end, screening patients at high risk for breast cancer with the addition of annual breast MRI has been added to screening recommendations.


The preceding paragraphs describe the screening of patients who do not have significant breast symptoms. All patients with clinical evidence of significant or potentially significant breast disease should undergo a diagnostic mammogram and subsequent work-up as necessary. Diagnostic mammograms are problem-solving examinations in which specific projections are obtained to rule out cancer or to show a suspicious area seen on the routine screening projections. They are also indicated if a woman presents with a palpable mass or other symptom. The area of interest may be better shown using image enhancement methods, such as spot compression and magnification technique. Further work-up may be necessary if mammography does not show a correlative mass. Alternative imaging modalities such as ultrasonography are often used to complete a successful work-up. The radiologist and radiographer direct and conduct the diagnostic mammogram to facilitate an accurate interpretation.


Although most diagnostic mammograms conclude with probable benign findings, some women are asked to return for subsequent mammograms in 3 or 6 months to assess for interval changes. Other women must consult with a specialist or surgeon about possible options such as fine-needle aspiration biopsy (FNAB), core biopsy, or excisional biopsy.


Although it is an excellent tool for detecting breast cancer, mammography does not permit diagnosis of breast cancer. Some lesions may appear consistent with malignant disease but turn out to be completely benign conditions. Breast cancer can be diagnosed only by a pathologist through the evaluation of tissue extracted from the lesion. After interpreting the diagnostic work-up, the radiologist must carefully determine whether surgical intervention is warranted.



RISK FACTORS


Assessing a woman’s risk for developing breast cancer is complicated. An accurate patient history must be elicited to identify potential individual risk factors. The radiologist considers these known risks after interpreting the mammogram. Other than gender, factors that are known to influence the development of breast cancer include age, hormonal history, and family history.





Family history


A woman whose daughter, sister, or mother previously developed breast cancer, especially at an early age, is at higher risk of developing the disease. Studies have shown, however, that only 13.6% of known breast cancers are found in women with a family history of the disease. A true genetic disorder has been identified in only 5% to 10% of women with breast cancer.1 Although family history is an important risk factor, women with no family history should be aware that they are also at risk.


In 1994, researchers isolated two breast cancer genes—BRCA1 and BRCA2. Commercial screening tests subsequently were developed. Studies have found that men and women with these genes have a higher risk of developing not only breast cancer but also other cancers, such as ovarian cancer and testicular cancer. Widespread genetic testing has raised ethical concerns associated with identifying appropriate candidates for genetic screening and determining what is done with the information derived from the testing. These concerns have been addressed; the Genetic Information Nondiscrimination Act (GINA) became a federal law in 2008.




Breast


The terms breast and mammary gland are often used synonymously. Anatomy textbooks tend to use the term mammary gland, whereas radiography textbooks tend to use the term breast. The breasts (mammary glands) are lobulated glandular structures located within the superficial fascia of the anterolateral surface of the thorax of both males and females. The mammary glands divide the superficial fascia into anterior and posterior components. The mammary tissue is completely surrounded by fascia and is enveloped between the anterior and posterior layers of the superficial fascia. In females, the breasts are secondary sex characteristics and function as accessory glands to the reproductive system by producing and secreting milk during lactation. In males, the breasts are rudimentary and without function. Male breasts are only rarely subject to abnormalities, such as neoplasms, that require radiologic evaluation.


Female breasts vary considerably in size and shape, depending on the amount of fat and glandular tissue and the condition of the suspensory ligaments. Each breast is usually cone-shaped, with the base or posterior surface of the breast overlying the pectoralis major and serratus anterior muscles. These muscles extend from the second or third rib inferiorly to the sixth or seventh rib and from near the lateral margin of the sternum laterally toward the anterior axillary plane. An additional portion of breast tissue, the axillary prolongation or axillary tail (AT), extends from the upper lateral base of the breasts into the axillary fossa (Fig. 23-4).



The breast tapers anteriorly from the base, ending in the nipple, which is surrounded by a circular area of pigmented skin called the areola. The breasts are supported by Cooper ligaments, suspensory ligaments that extend from the posterior layers of the superficial fascia through the anterior fascia into the subcutaneous tissue and skin. It is the condition of these ligaments, and not the relative fat content, that gives the breasts their firmness or lack of firmness.


The adult female breast consists of 15 to 20 lobes, which are distributed such that more lobes are superior and lateral than inferior and medial. Each lobe is divided into many lobules, which are the basic structural units of the breast. The lobules contain the glandular elements, or acini. Each lobule consists of several acini, numerous draining ducts, and the interlobular stroma or connective tissue. These elements are part of the breast parenchyma and participate in hormonal changes. By the late teenage years to early 20s, each breast contains several hundred lobules. The lobules tend to decrease in size with increasing age and particularly after pregnancy—a normal process called involution.


The openings of each acinus join to form lactiferous ductules that drain the lobules, which join to form 15 to 20 lactiferous ducts, one for each lobe. Several lactiferous ducts may combine before emptying directly into the nipple. As a result, there are usually fewer duct openings on the nipple than there are breast ducts and lobes. The individual lobes are incompletely separated from each other by the Cooper ligaments. The space between the lobes also contains fatty tissue and additional connective tissue. A layer of fatty tissue surrounds the gland except in the area immediately under the areola and nipple (Fig. 23-5).



The lymphatic vessels of the breast drain laterally into the axillary lymph nodes and medially into the chain of internal mammary lymph nodes (see Fig. 25-6). Approximately 75% of the lymph drainage is toward the axilla, and 25% of the drainage is toward the internal mammary chain. The number of axillary nodes varies from 12 to 30 (sometimes more). The axilla is occasionally radiographed during breast examinations to evaluate the axillary nodes. The internal mammary nodes are situated behind the sternum and manubrium and, if enlarged, are occasionally visible on a lateral chest radiograph.


The radiographer should take into account breast anatomy and patient body habitus to image as much breast tissue as possible successfully. Image receptor (IR) size must be appropriate for the breast being imaged. Larger breasts would not be entirely shown on small IRs. Conversely, smaller breasts should not be imaged on larger IRs because (1) other body structures may interfere with the compression device and produce an unacceptable image, and (2) the pectoral muscle and the skin are likely to become taut from upward stretching of the arm, preventing the breast tissue from being completely pulled onto the film.


The natural mobility of the breast is also an important consideration. The lateral and inferior aspects of the breast are mobile, whereas the medial and superior aspects are fixed. The breast should always be positioned by moving the mobile aspects toward the fixed tissues. Likewise, the radiographer should avoid moving the compression paddle against fixed tissues because this would cause less breast tissue to be imaged.



Tissue Variations


The glandular and connective tissues of the breasts are soft tissue–density structures. The ability to show radiographic detail within the breast depends on the fat within and between the breast lobules and the fat surrounding the breasts. The postpubertal adolescent breast contains primarily dense connective tissue and casts a relatively homogeneous radiographic image with little tissue differentiation (Fig. 23-6). The development of glandular tissue decreases radiographic contrast. During pregnancy, significant hypertrophy of glands and ducts occurs within the breasts. This change causes the breasts to become extremely dense and opaque. After the end of lactation, considerable involution of glandular and parenchymal tissues usually occurs, and these tissues are replaced with increased amounts of fatty tissue. Fat accumulation varies markedly among individuals. This normal fat accumulation significantly increases the natural radiographic contrast within the breasts (Fig. 23-7). The breasts of patients with fibrocystic parenchymal conditions may not undergo this involution (Fig. 23-8).





The glandular and connective tissue elements of the breast can regenerate as needed for subsequent pregnancies. After menopause, the glandular and stromal elements undergo gradual atrophy (Fig. 23-9). External factors such as surgical menopause and ingestion of hormones may inhibit this normal process. From puberty through menopause, mammotrophic hormones influence cyclic changes in the breasts. The glandular and connective tissues are in a state of constant change (Fig. 23-10).









Breast Imaging



EVOLUTION OF MAMMOGRAPHY SYSTEMS


Because the breast is composed of tissues with very similar densities and effective atomic numbers, little difference in attenuation is noticed when conventional x-ray equipment and technique are used. Manufacturers have developed imaging systems that optimally and consistently produce images with high contrast and resolution.


Diligent research and development began in the 1960s, and the first dedicated mammography unit was introduced in 1967 by CGR (France) (Fig. 23-11). In the 1970s, increased awareness of the elevated radiation doses prevalent in mammography served as the catalyst for the rapid progression of imaging systems. In the 1970s and early 1980s, xeromammography, named for the Xerox Corporation that developed it, was widely used (see Fig. 23-2). This method used much less radiation than the direct-exposure, silver-based films that were available. Eventually, film manufacturers introduced several generations of mammography film-screen systems that used even less exposure and improved tissue visualization. Each subsequent new system showed improvement in contrast and resolution while minimizing patient dose.



In the 1980s, the ACR accreditation program established quality standards for breast imaging to optimize mammographic equipment, processors, and screen-film systems to ensure the production of high-quality images. This program was expanded in the 1990s to include quality control and personnel qualifications and training. The voluntary ACR program has become the model from which MQSA operates, and the ACR has been instrumental in designing the clinical practice guidelines for quality mammography in the United States. The evolution of mammography has resulted in the implementation of radiographic systems designed specifically for breast imaging.



MAMMOGRAPHY EQUIPMENT


In recent years, equipment manufacturers have produced dedicated mammography units that have high-frequency generators, various tube and filter materials, focal spot sizes that allow tissue magnification, and specialized grids to help improve image quality and streamlined designs and ergonomic patient positioning aids.


The high-frequency generators offer more precise control of kilovolt (peak) (kVp), milliamperes (mA), and exposure time. The linearity and reproducibility of the radiographic exposures using high-frequency generators is uniformly excellent. The greatest benefit of these generators may be the efficient waveform output that produces a higher effective energy x-ray beam per set kVp and mA. High-frequency generators are not as bulky, and they can be installed within the single-standing mammography unit operating on single-phase incoming line power, facilitating easy installation and creating a less intimidating appearance (Fig. 23-12).



Specialized grids were developed for mammography during the 1980s to reduce scatter radiation and increase the image contrast in mammography. Most units employ moving linear focused grids, but some manufacturers have developed very specialized grids. The Hologic (Lorad) High Transmission Cellular (HTC) Grid employs a honeycomb-pattern, multidirectional design. All dedicated mammography units today, with the exception of slit-scan digital units, still employ grids.


As manufacturers of dedicated mammography equipment sought to improve image quality, they have tried many different combinations of tube and filter materials. The most widely accepted combinations used at this time are molybdenum target with molybdenum filter (Mo/Mo), molybdenum target with rhodium filter (Mo/Rh), or rhodium target with rhodium filter (Rh/Rh). Mo/Mo is used most often, but Mo/Rh and Rh/Rh are used for better penetration of denser breasts with thick tissues.


The manufacturers also knew that technologists and physicians were interested in the comfort of their patients. They worked to make the examination more tolerable for patients, more ergonomically acceptable, and more efficient for the technologist performing the examination, while developing positioning aids to increase visualization of the tissue. Some of these aids include rounded corners on Bucky devices and compression paddles, the automatic release of compression after exposure, and foot pedal controls.


Finally, to bring mammography into the digital world was no simple task. To achieve the resolution and detail necessary for breast imaging, entire systems, from acquisition to diagnostic review workstations, were developed by competing manufacturers. Each of these included proprietary components that made integration of the units into a current picture archiving and communication system (PACS) network difficult. Integrating the Healthcare Enterprise has brought manufacturers of the many components necessary in a full field digital mammography (FFDM) system together to work out problems of compatibility and language allowing facilities the opportunity to transition more seamlessly into digital mammography



METHOD OF EXAMINATION


Because of the sensitivity of the radiographic films and imaging techniques used for mammography, artifacts are common. It is advisable to dress patients in open-front gowns because the breast must be bared for the examination. Patients should remove any deodorant and powder from the axilla region and breast because these substances can resemble calcifications on the resultant image. Before the breast is radiographed, a complete history is taken, and a careful physical assessment is performed, noting all biopsy scars, palpable masses, suspicious thickenings, skin abnormalities, and nipple alterations (Fig. 23-13).



Both breasts are routinely radiographed obtaining craniocaudal (CC) and mediolateral oblique (MLO) projections. Image enhancement methods, such as spot compression and magnification technique, are often useful. It is sometimes necessary to enhance images or vary the projections to characterize lesions and calcifications better. In symptomatic patients, the examination should not be limited to the symptomatic breast. Both breasts should be examined for comparison purposes and because significant radiographic findings may be shown in a clinically normal breast.



EXAMINATION PROCEDURES


This section describes procedures for conducting mammographic examinations using dedicated systems. The following steps should be taken:



• If possible, examine previous mammographic studies of patients who are undergoing subsequent mammography screening. These images should be evaluated for positioning, compression, and exposure factors to determine whether any improvement in image quality is required for the current study. Position the breast consistently so that any lesion can be accurately localized and a valid comparison can be made with prior studies.


• Determine the correct IR size for the patient, and use the smallest possible size to image all of the breast tissue fully. Positioning the breast on a surface that is too large causes the skin and muscles to overextend, reducing the amount of posterior tissue imaged.


• Explain the procedure simply and completely to the patient before beginning the examination. It should never be assumed that the patient is fully aware of what the mammographer is about to do, even if the patient has had prior examinations.


• In many cases, the routine projections do not sufficiently show all of the breast tissue, and additional projections may be necessary. To allay patient concerns, the mammographer should explain to the patient before beginning the procedure why additional projections are sometimes needed and that they do not indicate a potential problem.


• Before positioning the patient’s breast and applying compression, consider the natural mobility of the breast so that patient discomfort can be minimized. The inferior and lateral portions of the breast are mobile, whereas the superior and medial portions are fixed. Whenever possible, the mobile tissues should be moved toward the fixed tissues.


• For each of the two basic breast projections, ensure that the breast is firmly supported and adjusted so that the nipple is directed forward.


• Profile the nipple, if possible. Obtaining an image of the posterior breast tissue should be the primary consideration, and positioning of the nipple in profile is not always possible. An additional projection to profile the nipple can be obtained if necessary. Alternatively, a marker may be used to locate clearly the nipple that is not in profile, in which case an additional image may not be needed.


• Apply proper compression to the breast. Compression is an important factor in achieving a high-quality mammogram. The primary objective of compression is to produce uniform breast thickness from the nipple to the posteriormost aspect of the breast. Properly applied compression spreads the breast so that the tissue thickness is more evenly distributed over the image and better separation of the glandular elements is achieved. A rigid, radiolucent mammography compression paddle facilitates breast compression. Generally, compression is applied initially using a hands-free control and then applied manually during the final phase of compression. The compression should be taut but not painful. The skin of a properly compressed breast should feel tight when lightly tapped with the fingertips. When evaluating images, compare the degree of compression with previous mammograms and note any variations. If a patient is unable to tolerate an adequate amount of compression, document this information on the patient history form for the radiologist.


• Place identification markers (Fig. 23-14) according to the following standard convention:




• Mammography film labeling may also include the following:



• For patients with palpable masses, a radiopaque (BB or X-spot) marker may be used to identify the location of the mass. A different type of radiopaque marker may be used to identify skin lesions, scars, or moles. This is determined by the policy of the facility.


• When using automatic exposure control (AEC), position the variable-position detector at the chest wall, the mid-breast, or the anterior breast, depending on breast composition and size. The appropriate location of the AEC detector must be determined for each individual patient. If possible, the detector should be placed under the most glandular portion of the breast, usually just posterior to the nipple.


• When reviewing images, assess contrast and density for optimal differentiation of breast tissues. Anatomic markers should be visible. The projections of one breast should be compared with the same projections of the contralateral breast to evaluate symmetry and consistency of positioning. All images should be absent of motion blur, artifacts, and skin folds. Images must be evaluated for potentially suspicious lesions and calcifications that may require image enhancement methods.


• To evaluate whether sufficient breast tissue is shown, the radiographer should measure the depth of the breast from the nipple to the chest wall on the CC and MLO projections. The posterior nipple line (PNL) is an imaginary line that is “drawn” obliquely from the nipple to the pectoralis muscle or edge of the image, whichever comes first on the MLO projection. On the CC projection, the PNL is “drawn” from the nipple to the chest wall or to the edge of the image, whichever comes first. The PNL on the CC should be within ⅓ inch (1 cm) of depth of the PNL on the MLO projection (Fig. 23-15).



• Between examinations, use a disinfectant to clean the image receptor tray surface, compression paddle, patient handle grips, and face guard.


• If practical, a heating pad or commercially available mammography image receptor cover may be used to warm the image receptor tray surface and to enhance patient comfort.


• Mammography is a team effort involving the patient and the mammographer. Acknowledge the individual needs of each patient to facilitate the cooperation and trust necessary to complete the procedure successfully. The nature of the interaction between the radiographer and the patient is likely to determine whether the patient chooses to have subsequent mammograms.



Summary of Mammography Projections


Before beginning to learn mammography projections, the student of radiography should carefully study the illustrative summary of mammography projections shown in the box. Familiarity with the different projection names and abbreviations would enhance the student’s understanding of the detailed discussions of the projections presented in this chapter.



DESCRIPTIVE TERMINOLOGY


Descriptive terminology has been developed for the referring physician, the technologist, and the radiologist all to communicate efficiently regarding an area of concern within a breast. When describing an area of concern, the laterality (right or left) must accompany the description (Fig. 23-16).



The breast is divided into four quadrants: the upper-outer quadrant (UOQ), lower-outer quadrant (LOQ), upper-inner quadrant (UIQ), and lower-inner quadrant (LIQ). Clock-time is also used to describe the location of a specific area of concern within the breast: 2:00 in the right breast is in the UIQ, whereas 2:00 in the left breast is in the UOQ. This opposite labeling applies to all clock-times; it is important to identify the correct breast, clock-time, and quadrant. The distance of the abnormality from the nipple, which is the only fixed point of reference in the breast, is also noted. The terms subareolar and periareolar describe the area directly beneath the nipple and near (or around) the nipple area.



Routine Projections of the Breast


Mammography is routinely performed using the CC and MLO projections.





imageCRANIOCAUDAL (CC) PROJECTION







Position of part:



• While standing on the medial side of the breast to be imaged, elevate the inframammary fold to its maximal height.


• Adjust the height of the C-arm to the level of the inferior surface of the patient’s breast.


• Use both hands to pull the breast gently onto the image receptor holder, while instructing the patient to press the thorax against the image receptor. Have the patient lean slightly forward from the waist.


• Keep the breast perpendicular to the chest wall. The technologist should use his or her fingertips to pull the posterior tissue gently forward onto the IR.


• Center the breast over the AEC detector, with the nipple in profile if possible.


• Immobilize the breast with one hand, being careful not to remove this hand until compression begins.


• Use the other hand to drape the opposite breast over the corner of the image receptor. This maneuver improves demonstration of the medial tissue.


• Have the patient hold onto the grab bar with the contralateral hand; this helps steady the patient as you continue positioning.


• Placing your arm against the patient’s back with your hand on the shoulder of the affected side, make certain the patient’s shoulder is relaxed and in external rotation.


• Rotate the patient’s head away from the affected side.


• Lean the patient toward the machine, and rest the patient’s head against the face guard.


• Make certain no other objects obstruct the path of the beam.


• With the hand on the patient’s shoulder, gently slide the skin up over the clavicle.


• Using the hand that is anchoring the patient’s breast, pull the lateral tissue on the image receptor without sacrificing medial tissue.


• Inform the patient that compression of the breast will be used. Bring the compression paddle into contact with the breast while sliding the hand toward the nipple.


• Slowly apply compression until the breast feels taut.


• Check the medial and lateral aspects of the breast for adequate compression.


• Instruct the patient to indicate whether the compression becomes uncomfortable.


• After full compression is achieved and checked, move the AEC detector to the appropriate position, and instruct the patient to stop breathing (Fig. 23-17).



• Make the exposure.


• Release breast compression immediately.




Structures shown: The CC projection shows the central, subareolar, and medial fibroglandular breast tissue. The pectoral muscle is shown in approximately 30% of all CC images.1





imageMEDIOLATERAL OBLIQUE (MLO) PROJECTION







Position of part:



• Determine the degree of obliquity of the C-arm apparatus by rotating the tube until the long edge of the image receptor is parallel to the upper third of the pectoral muscle of the affected side. The degree of obliquity should be between 30 degrees and 60 degrees, depending on the patient’s body habitus.


• Adjust the height of the C-arm so that the superior border is level with the axilla.


• Instruct the patient to elevate the arm of the affected side over the corner of the image receptor and to rest the hand on the adjacent handgrip. The patient’s elbow should be flexed and resting posterior to the image receptor.


• Place the upper corner of the image receptor as high as possible into the patient’s axilla between the pectoral and latissimus dorsi muscles so that the image receptor is behind the pectoral fold.


• Ensure that the patient’s affected shoulder is relaxed and leaning slightly anterior. Placing the flat surface of the hand along the lateral aspect of the breast, gently pull the patient’s breast and pectoral muscle anteriorly and medially.


• Holding the breast between the thumb and fingers, gently lift it up, out, and away from the chest wall.


• Rotate the patient’s body toward the image receptor while asking the patient to bend slightly at the waist.


• Center the breast with the nipple in profile if possible, and hold the breast in position.


• Hold the breast up and out by rotating the hand so that the base of the thumb and the heel of the hand support the breast (fingers are pointing away from breast).


• Inform the patient that compression of the breast will be used. Continue to hold the breast up and out while sliding the hand toward the nipple as the compression paddle is brought into contact with the breast.


• Slowly apply compression until the breast feels taut. The corner of the compression paddle should be inferior to the clavicle.


• Check the superior and inferior aspects of the breast for adequate compression.


• Instruct the patient to indicate whether the compression becomes uncomfortable.


• Pull down on the patient’s abdominal tissue to open the inframammary fold.


• Instruct the patient to hold the opposite breast away from the path of the beam.


• After full compression is achieved, move the AEC detector to the appropriate position, and instruct the patient to stop breathing (Fig. 23-19).



• Make the exposure.


• Release breast compression immediately.




Structures shown: The MLO projection usually shows most of the breast tissue, with emphasis on the lateral aspect and AT.





Routine Projections of the Augmented Breast


Mammography is clearly the preferred and most reliable technique for breast cancer screening. This technique has an 80% to 90% true-positive rate for detecting cancer in breasts that do not contain implants. For the millions of women in the United States who have undergone augmentation mammoplasty for cosmetic or reconstructive purposes, the true-positive (pathologic-mammographic) breast cancer detection rate decreases to approximately 60%, however, because implants can obscure 85% of breast structures, potentially hiding a small cancer that could normally be detected with mammography at an early and curable stage.


Successful radiography of an augmented breast requires a highly skilled mammographer. During the examination, precautions must be taken to avoid rupture of the augmentation device.


Mammography of the augmented breast presents a challenge that cannot be met with the standard two-image examination of each breast. An eight-radiograph examination is preferred whenever possible. The posterior and superior aspects of the augmented breast can be satisfactorily evaluated using the CC and MLO projections. These four images do not adequately show the surrounding breast parenchyma, however.


The initial two projections may be combined with the Eklund, or implant displaced (ID), technique. For the Eklund method, the implant is pushed posteriorly against the chest wall so that it is excluded from the image, and the breast tissue surrounding the implant is pulled anteriorly and compressed. This positioning improves compression of breast tissue and visualization of breast structures. The CC and MLO projections are often performed using the ID technique.


Complications frequently associated with breast augmentation include fibrosis, increased fibrous tissue surrounding the implant, shrinking, hardening, leakage, and pain. Because mammography alone cannot fully show all complications, ultrasonography and MRI are also used for breast examinations in symptomatic patients. Whether ultrasonography or MRI is used as the adjunct imaging after mammography for patients with suspected implant rupture varies from practice to practice.


Ultrasonography of the breast has proved useful in identifying implant leakage when implant rupture is suggested by mammographic findings and clinical examination and occasionally when leakage is not suspected. It has also successfully identified leakage that has migrated to the axillary lymph nodes. Although ultrasonography is not yet recommended as a screening modality for implant leakage, it has enhanced the mammographic examination.


MRI is currently the most commonly used modality for diagnostic evaluation of augmented breasts. Although MRI offers several diagnostic advantages, the cost and time-consuming nature of the procedure inhibits its use as a screening modality for patients who have undergone augmentation. It may be used as a screening tool for women who have undergone reconstruction after breast cancer surgery. MRI has proved useful as a preoperative tool in locating the position of an implant, identifying the contour of the deformity, and confirming rupture and leakage migration patterns. The sensitivity and specificity of MRI have been 94% and 97%.1



CRANIOCAUDAL (CC) PROJECTION WITH FULL IMPLANT









Structures shown: The image should show the entire implant and surrounding posterior breast tissue with suboptimal compression of the anterior fibroglandular breast tissue (Fig. 23-21).






Augmented Breast



CRANIOCAUDAL PROJECTION WITH IMPLANT DISPLACED (CC ID)







Position of part:



• While standing on the medial side of the breast to be imaged, elevate the inframammary fold to its maximal height.


• Adjust the height of the C-arm to the level of the inferior surface of the breast.


• Standing behind the patient, place both arms around the patient and locate the anterior border of the implant by walking the fingers back from the nipple toward the chest wall.


• When the anterior border of the implant has been located, gently pull the anterior breast tissue forward onto the image receptor (Fig. 23-22). Use the hands and the edge of the image receptor to keep the implant displaced posteriorly.



• Center the breast over the AEC detector with the nipple in profile if possible.


• Hold the implant back against the chest wall. Slowly apply compression to the anterior skin surface, being careful not to allow the implant to slip under the compression paddle. As compression continues, the implant should be seen bulging behind the compression paddle.


• Apply compression until the anterior breast tissue is taut. Compared with the full-implant projection, an additional ¾ to 2 inches (2 to 5 cm) of compression should be achieved with the implant displaced.


• Instruct the patient to indicate whether the compression becomes uncomfortable.


• When full compression is achieved, move the AEC detector to the appropriate position and instruct the patient to stop breathing.


• Make the exposure.


• Release breast compression immediately.




Structures shown: This projection shows the implant displaced posteriorly. The anterior and central breast tissue is seen projected free of superimposition with uniform compression and improved tissue differentiation (Fig. 23-23).


Mar 3, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on MAMMOGRAPHY
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