Breast Imaging Essentials

Transcription

1 Breast Imaging Essentials Module 1 Transcript 2016 ASRT. All rights reserved.

2 Breast Imaging Essentials Module 1 - Fundamentals of Breast Imaging 1. ASRT Animation 2. Welcome Welcome to Module 1 of Breast Imaging Essentials Fundamentals of Breast Imaging. This module was written by Myke Kudlas, M.Ed., R.T.(R)(QM), CIIP, PMP 3. License Agreement 4. Objectives After completing this module, you will be able to: Discuss radiographic principles and how they apply to mammographic imaging. List technical factors and techniques that produce quality mammographic images while keeping patient radiation exposure to a minimum. Explain the development and purpose of digital mammography. Explain the purpose of regulations and licensing regarding performance of mammography. List additional breast imaging modalities. 5. Introduction Simply stated, mammography refers to radiography of breast tissue. There is nothing simple about the performance of mammographic procedures, however. From the construction of mammographic equipment to the techniques used for mammographic positioning, mammography is one of the most detail-dependent and highly regulated exams in the medical imaging spectrum. In fact, mammography is currently the only federally regulated radiographic procedure in the United States. This module introduces the fundamentals of mammography, personnel requirements, and basics of equipment design. 6. Breast Anatomy The breast is made up of 6 different types of tissues: milk-producing glands called lobules, ducts that carry milk from the glands to the nipple, fatty tissue, connective tissue, blood vessels, and lymph vessels. Although breast cancer can begin in any of these tissues, the most common location for breast cancer formation is along the lining of the ducts. When breast cancer spreads from the breast to other parts of the body, it is generally spread via the lymph vessels. 7. Breast Cancer Statistics The National Cancer Institute reports that the mortality rate from breast cancer has been steadily declining since Although many factors account for this decrease in the mortality rate, screening mammography certainly has played a significant part in this positive trend. According to the most recent statistics from the American Cancer Society, more than 230,000 new cases of breast cancer are diagnosed in the United States each year. In addition, about 40,000 women die of breast cancer annually and there are around 62,500 in situ cases. Breast cancer is the second-leading cause of cancer deaths behind lung cancer. Screening mammography refers to breast imaging for asymptomatic women. A screening study is performed as an effort to catch the disease early and allow time for cancer to be treated before it can spread to other critical organs. Mammography is a very important tool in the fight against breast cancer. Currently, the American Cancer Society recommends routine screening mammograms to detect the early onset of breast cancer for women 45 and older. 8. Imaging the Breast

3 Mammography is unique among medical imaging exams. Compared to imaging of other parts of the body, the breast is very uniform in anatomic density. For example, when imaging a hand or knee, the appearance of bony structures differs significantly from the soft tissues surrounding them. However, the glandular and fatty tissues that make up the breast are very similar to one another. It also can be difficult to differentiate normal tissue from certain masses and lesions in the breast. Breast tissue is unique to each individual and can vary from fatty to dense and fibrous. Unlike an arm or even an abdomen, the technical factors used to produce the best quality radiograph can t be selected by looking at a patient or measuring the anatomy. This is the primary reason that automatic exposure techniques are used in mammography instead of manual techniques. 9. Modern Mammography Equipment The era of modern mammography equipment began with the introduction of a Philips dedicated mammography unit that incorporated a reciprocating grid. This was the first time that grids had been used in mammography to absorb scatter radiation and help improve contrast. Other modern components of this unit included a foot pedal that operated a power-driven breast compression paddle, a choice between different types of filter materials, a microfocus focal spot, and a high-output generator. Although current mammography equipment has additional components and improvements, our modern units still bear a striking resemblance to the 1978 design. 10. High-frequency Generators High-frequency generators are used in all mammography units to produce the power necessary for image production. In fact, it s difficult to find any kind of imaging equipment that uses anything other than highfrequency power generators. Compared with single-phase or 3-phase generators, high-frequency generators produce a consistent level of power. The waveforms from a single-phase generator demonstrate that power fluctuates greatly from essentially no power generation to the peak kilovolt setting. This means that a tube with a singlephase power generator creates x-rays that are emitted in a pulsing manner and have a wide variation in beam strength. X-ray tubes using a high-frequency generator, on the other hand, produce streams of x-rays that are more consistent, more homogeneous, and can be controlled precisely. Small changes in x-ray production can cause noticeable differences in the resulting image. Therefore, it s critical in mammography to use high-frequency generators so that adjustments can be made to technical factors such as kvp, ma and time settings. 11. kvp Perhaps the most surprising aspect of mammographic technique for a nonmammographer is the use of extremely low kvp settings. The kvp settings in mammography range from 20 to 40, depending on the manufacturer. This compares with kvp settings of 50 to at least 150 for conventional radiography equipment. Since breast tissue is largely homogeneous, with very little differentiation between fatty, fibrous and glandular tissues, very high-contrast images are required to distinguish among tissue types. Using kvp settings of 20 to 40 creates an x-ray beam that is softer, has low energy, produces less scatter radiation, and results in higher radiographic contrast. The biggest disadvantage of using low kvp settings is that it increases absorption and, therefore, radiation dose to the patient. The x-ray beam is made up of essentially 3 types of x-rays: lower-energy x-rays that are absorbed by the skin or surface tissues; higher-energy x-rays that strike the image receptor without interacting with any anatomy; and diagnostic x-rays that are absorbed when they strike and pass through the tissue. 12. Diagnostic X-rays in Mammography In mammography, diagnostic x-rays are produced when the kvp setting is between 20 and 40. If the mammographer were to adjust the kvp setting to a high level, in the range of 80 kvp, most of the x-rays

4 would pass through the anatomy and strike the image receptor. The resulting image would be overexposed. If the mammographer were to adjust the kvp setting down to 5 kvp, almost all of the x-rays would be absorbed by the breast tissue and the image would be underexposed. A setting between 20 and 40 kvp helps to maximize the production of diagnostic x-rays for mammography. 13. X-ray Emission Spectrum An x-ray emission spectrum is a graph that represents all of the x-rays exiting the tube during an exposure and their relative strengths. For example, during a radiographic exposure made using a kvp setting of 93, the majority of the x-rays are produced by the bremsstrahlung process, with a small peak of characteristic x-rays created at 69.5 kiloelectron volts, or kev. Very few x-rays remain below 10 kev because they have been removed by aluminum filtration. The strongest photon exiting the x-ray tube has an energy of 93 kev, which reflects the kvp setting of 93. Several factors affect the size and shape of the emission spectrum, including technique, the anode target material, and added filtration. 14. Target/Filter Combinations Both the tube target material and filtration selection influence the strength and quality of the x-ray beam, which has a direct relationship to patient radiation dose and image quality. Using different target and filter combinations is another way to maximize the production of x-rays in the diagnostic range. In diagnostic radiography, the target of the anode is usually constructed of a tungsten alloy, and aluminum filters are used to remove the lower-energy x-rays that increase patient dose but do not contribute greatly to the finished image. Since the x-rays produced in a mammographic tube are much weaker, other types of filtration and target materials also are used to enhance the quality of the x-ray beam. In fact, many mammography units permit the mammographer to select the optimal target and filter combination for specific breast types and thicknesses. Filtration materials in mammography include molybdenum, rhodium, silver, or aluminum. These materials allow most x-rays to pass through if they are in the diagnostic range and have a higher energy, but they attenuate or absorb most of the lower-energy x-rays that add little diagnostic information to the image and increase patient dose. The common target materials used in mammography are molybdenum, rhodium, and tungsten. These target materials are capable of producing diagnostic x-rays in the sweet spot of 17 to 24 kev for mammography. 15. Target Materials Each target material produces a different emission spectrum given the same kvp setting. When a tungsten target and an aluminum filter is used with a kvp setting of 26, the emission spectrum shows that most of the x-rays have a kev of about 20. This target and filter combination produces diagnostic x-rays within the 17 to 24 kev sweet spot, and the amount of lower-energy x-rays that only add to patient dose is relatively low. However, the number of higher-energy x-rays that pass through the anatomy and strike the image receptor is high. For this reason, tungsten targets are more commonly used in digital mammography units. When a molybdenum target is used with a molybdenum filter and the same 26 kvp setting, the x-ray distribution is quite different from that of the tungsten target. Fewer lower-energy x-rays exit the tube, and much fewer higher-energy x-rays are produced. There is also a very large characteristic peak at 17 kev and a smaller characteristic peak at 20 kev. Therefore, a molybdenum target with a molybdenum filter produces the largest number of x-rays at the low end of the sweet spot for diagnostic x-rays, making this target/filter combination ideal for breast tissue that is fatty and easier to penetrate. The distribution of x-rays using a rhodium target and filter combination looks fairly similar to the molybdenum emission spectrum; however, the characteristic peaks are higher at 20 and 23 kev, and slightly more lower-energy x-rays escape from the x-ray tube. This combination produces characteristic x- rays at the top of the diagnostic range for mammographic imaging and makes a rhodium target and filter combination an excellent choice for women with dense or fibrous breast tissue.

5 Various mammographic units use multiple combinations of target and filter materials depending on the manufacturer. Many allow the mammographer to choose between 2 different target materials and then further choose filtration materials. For example, a molybdenum target and a rhodium filter may be used to produce a slightly stronger x-ray beam than that generated by a molybdenum/molybdenum combination. 16. Knowledge Check 17. Knowledge Check 18. Anode-Heel Effect The anode is the positive side of the x-ray tube that is bombarded with electrons during x-ray production. In mammography units, the anode side of the x-ray tube is positioned toward the nipple rather than the chest wall side of the patient. This orientation ensures that the image acquisition process takes advantage of the anode-heel effect. The x-ray beam is not totally homogeneous in terms of x-ray strength; the anode side of the beam is slightly weaker, and the cathode side of the beam is slightly stronger. This characteristic can be advantageous in mammography because there is more tissue at the chest wall and less tissue toward the nipple. By orienting the x-ray tube so that the stronger cathode side is toward the chest wall, more x-rays are available to penetrate the thicker chest wall, fewer x-rays penetrate the thinner nipple region, and an image of consistent quality is produced. If the tube was reversed and lower-energy x-rays were directed to the thicker chest wall side, the resulting image would be overexposed at the nipple and underexposed at the chest wall. 19. Divergent X-ray Beam The divergent nature of the x-ray beam could be detrimental to mammographic imaging if not managed properly. X-rays travel in essentially straight lines as they exit the x-ray tube, but they are not parallel to one another. The x-rays diverge, or move away from each other, as they exit the tube. This is similar to how light rays diverge from a light bulb. If you ve ever moved your hand toward a light source to make the shadow appear larger on the wall, you ve seen divergence in action. Virtually all general radiographic equipment places the center of the x-ray tube, the focal spot, directly over the center of the image receptor. The portion of the x-ray beam that travels from the focal spot to the center of the image receptor without diverging is called the central ray. Most radiographers are accustomed to centering the patient with this central ray to ensure that all anatomy is displayed on the image receptor. The disadvantage of divergent x-rays in mammography is that if the central ray is directed to the center of the image receptor, some of the chest wall tissue will be missed. The x-rays that strike the edge of the image receptor at the chest wall enter at an angle, and a triangular section of breast tissue is missed. Any lesion that may be present in this area will not be visible to the radiologist on the final image. 20. Tube Orientation To compensate for the divergent nature of the x-ray beam, manufacturers of mammographic equipment orient the x-ray tube in one of two ways. The first orientation is to move the tube as close to the patient as possible and cover the cathode side of the x-ray beam with lead or another type of shielding. This design moves the central ray to the chest wall edge of the image receptor so that a perpendicular x-ray beam strikes the image receptor and no tissue is missed. The second way that manufacturers have solved this problem is to slightly angle the x-ray tube so that the cathode is just above the anode. This orientation causes the x-rays of the cathode side of the divergent beam to be perpendicular to the image receptor at the chest wall and angles the central ray to the image receptor. The resulting image includes all chest wall tissue as well as any pathology in the region. 21. Focal Spot

6 The focal spot is an important component of x-ray tube construction that helps improve the visualization of fine details necessary for quality breast imaging. The focal spot is the area of the anode where the x- rays are actually produced. Because almost all mammographic equipment uses a rotating disk as an anode to dissipate heat, the focal spot is actually more of a focal track; x-rays are produced in a circle around the rotating anode. With all other factors remaining the same, the size of the focal spot equates to the spatial resolution seen on the finished image. Large focal spots produce decreased spatial resolution, and small focal spots produce increased spatial resolution. In conventional radiographic equipment, the size of the focal spot ranges from 0.6 to 1.2 mm. This focal spot size produces excellent spatial resolution for general radiographic imaging of bones, organs and vessels, but does not provide the spatial resolution needed to demonstrate the fine details inherent in breast tissue. Mammographic tubes use much smaller focal spot sizes, ranging from 0.1 to 0.3 mm. A disadvantage of reducing the size of the focal spot is that it can increase wear to the anode. Imagine all of the electrons that bombard a focal spot 1.2 mm wide being focused to an area only 0.1 mm wide. However, the decreased technical factors used in mammographic imaging help to limit the damage because fewer electrons strike the anode compared with general radiographic imaging. 22. Grids The use of radiographic grids increases image contrast by absorbing some of the scattered radiation before it reaches the image receptor. Although mammographic imaging produces little scatter radiation, high contrast is very important to a quality mammogram. The grids used in mammography have a ratio of 4:1 or 5:1. These ratios are much lower than the 6:1 to 16:1 grids used in general radiography in order to keep the radiographic exposure at satisfactory levels. During exposure, mammographic grids move in a single stroke across the image receptor, rather than moving back and forth as they do in general radiography. The grid strips are made of lead; however, the interspace materials for mammography grids are carbon fiber so that the productive x-ray beam can still penetrate the grid. The grid lines are blurred during image acquisition because of the short exposure times used in some mammographic applications, but mammographers must also ensure that grid lines do not appear on the final image. 23. Automatic Exposure Control (AEC) Automatic exposure control, or AEC, is used in most mammographic applications to reach an appropriate exposure level for a quality mammogram with acceptable levels of patient radiation exposure. Manual techniques are very difficult to set based on breast thickness alone because each patient s breast is unique in terms of tissue type and density. In general, manual techniques in mammography are only used when the patient has breast implants that would affect the operation of the AEC system. The AEC detector absorbs radiation until a predetermined amount is reached. At that time the AEC system terminates the exposure automatically. In most general radiography equipment, the AEC detector is located between the tabletop or chest board and the image receptor. This configuration would not work in mammography because high levels of contrast and spatial resolution are required, and the detector would be visible on the final image. For this reason, the AEC detector is located on the opposite side of the image receptor from the x-ray source. Radiation must pass through the patient and the image receptor before interacting with the AEC detector. The position of the detector can also be adjusted between the chest wall and the nipple based on breast size. 24. Magnification Magnification techniques are used in mammography to enlarge an area of interest. The technique takes advantage of the divergent nature of the x-ray beam: The closer the area of interest comes to the focal spot and the farther it is from the image receptor, the larger the area appears on the final image.

7 To magnify an area of interest, a base or platform is used to position the breast closer to the focal spot and farther from the image receptor. The entire breast generally does not appear on a magnified image, so it is important to place the area of interest as close as possible to the center of the imaging area. The light field from the collimator can help with this process. Magnification factors in mammography range from 1.5 to 2.0. Although the image is magnified, it can lose some spatial resolution during the process. To help maintain spatial resolution, the smallest focal spot available is used, generally 0.1 mm. In addition, the technique is adjusted to reduce the stress on the anode from using such a small focal spot. Grids are seldom used because the larger object-to-image receptor distance makes use of the air-gap technique to keep contrast at desired levels. When digital mammography was first implemented, it was hoped that the use of postprocessing techniques for image evaluation would reduce the number of additional images required. The intent was to replace additional magnification views with postprocessing zoom functions to evaluate microcalcifications. However, experience proved that electronically magnified images contain less information compared with evaluating calcifications using traditional magnification techniques. 25. Compression The breast compression paddle is undoubtedly the most intimidating part of the mammography unit, yet it is one of the most important. When compression is applied, breast tissue spreads out over a larger area, which ensures that as much anatomy as possible is demonstrated and that tissues do not overlap and hide potential pathologies. Also, because the breast tissue is closer to the image receptor, magnification is decreased and spatial resolution is improved. Image quality further improves with compressed, or thinner, tissue because less kvp is required. The end result is less scattered radiation, and more uniform tissue means exposure to the image receptor is uniform. Motion is also less of a problem when using compression because the compression device helps the patient remain still throughout the exam. Most importantly, radiation exposure to the patient is decreased because less radiation is needed to penetrate the compressed tissue. The compression device is made of thin plastic that does not greatly attenuate the x-ray beam. On most units, the mammographer controls the compression device using a foot pedal so that both hands are free to position the patient s breast tissue. A digital indicator displays the amount of compression measured in pounds or newtons. Appropriate compression ranges from 25 to 45 pounds; this amount provides tissue separation, improves image quality and reduces radiation exposure. On most mammographic units, the compression device is automatically released when the exposure is terminated. 26. Knowledge Check 27. Knowledge Check 28. Origins of Digital Mammography Digital imaging for diagnostic mammography had been discussed since the early 1990s. At a 1991 workshop funded by the National Cancer Institute, digital mammography was singled out as a future technology with great cancer-fighting potential. As a result, additional funding was provided to explore digital mammography. General Electric s Senographe became the first FDA-approved full-field digital mammography unit in the United States in January Digital imaging was already established for general radiography work, and digital systems were also being used in stereotactic breast biopsy. Digital mammography had not yet been accepted because of real and perceived problems with the quality of digital images and prohibitive costs. The greatest challenge in the design of digital mammography equipment was to develop a single image receptor large enough to cover the entire breast and to provide the high level of detail needed to demonstrate tiny lesions and the delicate anatomy of the breast. Only a full-field digital mammography system could make digital mammography a viable option.

8 In 2001, Medicare coverage was extended to patients receiving digital mammograms, which helped digital mammography become a more accepted form of breast imaging. 29. Digital vs Film-Screen Mammography After the introduction of digital mammography into clinical use, the question remained as to whether digital mammography quality was equal to film-screen quality. To answer this question, the National Cancer Institute funded the Digital Mammographic Imaging Screening Trial, or DMIST, in The trial involved 49,500 female volunteers who received both film-screen and digital mammograms. The results of the study were released in 2005 and showed that the quality of digital mammography exams was at least equal to the quality of film-screen mammography. Furthermore, digital quality was superior to filmscreen for women who were premenopausal, those who had dense breasts and women younger than 50 years old. Digital mammography has now been widely accepted. In August 2016, FDA statistics reported that there were 8,743 certified mammography facilities in the United States with 16,403 accredited mammography units. 16,137 of these units - greater than 98% - were digital as of this date. 30. Patient Benefits of Digital Mammography Many benefits of digital mammography have been recognized as facilities transitioned from film-screen to digital imaging. One of the most important benefits is the reduction in radiation dose to the patient. This results from the increased efficiency in digital image acquisition, as well as the wider latitude in digital imaging display that makes it possible to reduce the number of repeated images. Patients also appreciate the increased speed with which exams can be completed. The image is acquired and displayed within seconds, rather than minutes, which means that the mammographer can evaluate the need for additional imaging more quickly. If additional images are needed, the mammographer can acquire them within seconds and the patient does not have to leave the examination room. Also, the inconsistencies that occur during wet processing are eliminated, which further reduces delays and the need for repeated images. A common misconception among patients is that breast compression is not necessary in digital mammography. Because compression affects the geometric factors related to imaging, breast compression is still essential to producing quality images. 31. Facility Benefits of Digital Mammography Digital mammography has also greatly improved the workflow in mammography departments. Digital detectors have replaced cumbersome film cassettes, and the use of digital systems decreases the risk of misidentified or misplaced films. Digital systems also allow for postprocessing of the images and enables images to be evaluated by computer-aided detection devices. As an electronic record, the digital mammogram provides patients, mammographers and physicians much easier access. Images can be viewed in multiple places simultaneously and can be saved in multiple locations. The reduced procedure times associated with digital mammography also can increase productivity; mammographers can perform more studies on the same piece of equipment. This increase in productivity is necessary for mammography centers to survive the current economic demands of increased costs and reduced reimbursements. 32. Facility Benefits of Digital Mammography The radiologist s time is extremely valuable and is another important consideration when evaluating workflow processes. Within seconds of digital image acquisition and recording, the mammogram can be displayed and reviewed by the radiologist, who can manipulate the image using a variety of software tools. These tools include annotation features, hanging protocols, pan and zoom features, magnification, window/level function, and image inversion techniques. There is a learning curve associated with these tools and their use may initially increase interpretation times; however, with experience, interpretation times decrease and productivity and accuracy increase.

9 The reduction in time from acquisition to review also has had a positive effect on interventional procedures. Needle localization procedures are much quicker using digital technology because the images used to confirm needle position take only seconds to process and view. This significant increase in speed ensures better positioning, more accurate results, and enhanced patient comfort. All of these process improvements have had a positive impact on how breast imaging professionals deliver patient care. 33. Computer-Aided Detection (CAD) Computer-aided detection, or CAD, is a tool that is helpful in detecting breast abnormalities. The x-ray energy from the digital mammography image is transformed into electronic signals that can be transmitted very quickly. When the electronic data is sent to the CAD device, various software algorithms designed to recognize breast abnormalities such as calcifications and masses are applied. The CAD system marks areas of potential suspicion for further consideration by a radiologist. Many studies have indicated an increase in the cancer detection rate among interpreting physicians who use CAD. The increases were greatest among radiologists who interpret low volumes of mammograms. 34. Picture Archiving and Communication Systems (PACS) To store digital information, an imaging department uses a picture archiving and communication system, commonly known as PACS. As its name implies, PACS is an electronic method used to store and retrieve electronic data. PACS takes the place of file folders stored in a file room. Every PACS should be capable of performing 5 functions: 1. Image acquisition Interface with the digital equipment performing the image acquisition and recognize the digital data. 2. Image storage Store a large amount of image data securely. 3. Image transfer Quickly transfer large amounts of image information over an electronic network. 4. Image display Send image data to monitors and workstations so that the images display on the appropriate workstations in the proper format. 5. Image management Attach information to the images that identify and index the data correctly. The images acquired in digital mammography occupy a great deal of space in electronic form. A database usually provides for both short-term and long-term storage. Short-term storage holds the most recent images acquired, and retrieval of these images usually is faster than it is for those held in longterm storage. The size of a digital mammogram data file is often underestimated by PACS administrators who are not familiar with the resolution requirements in mammography. For example, a 4-projection mammography exam with CAD markings requires from 3 to 10 times the storage space of an average computed tomography examination. 35. Mammography Standards Equally as important as technology advancements has been the development of standards related to the production of mammographic images, the interpretation of mammograms, and qualifications of the personnel maintaining mammographic equipment. Until the mid-1980s, mammography standards varied widely from state to state and institution to institution. Mammograms were produced by general radiographers with varying degrees of educational preparation in the modality, and they were interpreted by radiologists with varying levels of expertise. In addition, the maintenance and quality control of the mammographic imaging chain were often random and inconsistent. In 1985 a Nationwide Evaluation of X-ray Trends, or NEXT, survey was conducted of facilities performing mammography. NEXT is a program jointly sponsored by state radiation control program directors and the federal government through the FDA Center for Devices and Radiological Health, or CDRH. The study

10 found wide variation in image quality, personnel preparation and technical factors used in mammographic imaging. The state of breast imaging was especially concerning to radiologists. Just 2 years after the release of the NEXT survey results regarding breast imaging, the American College of Radiology, or ACR, began its mammography accreditation program. In 1998 the ACR also became an active member of future NEXT programs by providing financial support. Today the NEXT program consists of representatives from the CDRH, the ACR, and the Conference of Radiation Control Program Directors. 36. ACR Accreditation Because of the many issues related to image quality and film processing identified by the NEXT study, the ACR began to explore the development of an accreditation program in A pilot program was implemented in 1987 and became the first accreditation program for mammography in the United States. The program was initially developed as a voluntary accreditation program that focused on film processing, phantom images, and the evaluation of clinical images. In addition, the accreditation guidelines outlined educational standards for mammographers, radiologists, and medical physicists engaged in breast imaging. Mammography accreditation expanded in 1990 when the first comprehensive manual for mammography quality control was published by the ACR. The manual outlines various equipment tests a mammographer must perform and lists 14 quality control tests that must be conducted annually by a qualified medical physicist. Although this manual has been revised over the years, it still is used today and is very similar in scope to the original 1990 manual. 37. ACR Mammography Phantom A major component of ACR accreditation is the ACR mammography phantom that was developed in early The phantom has a fairly simple design: A thick plastic block contains a wax insert that simulates 4.2 cm of breast tissue. The wax insert holds several features that can be seen on mammographic images if the equipment is functioning properly and if an appropriate technique is used. The insert contains 6 fibers, 5 speck groups and 5 masses. The fibers range in size from 0.4 to 1.56 mm; the speck groups range from 0.16 to 0.54 mm; and the masses vary from 0.25 to 2.0 mm. All these objects are rarely visible when the mammography phantom is imaged, but a minimum of 4 fibers, 3 speck groups and 3 masses must be identified by 2 individual medical physicists for a phantom image to meet accreditation standards. In addition, a glandular dose reading is taken during the exposure of the phantom; this dose reading must not exceed 3 mgy. 38. ARRT Mammography Certification As the ACR was perfecting its mammography accreditation program, the American Registry of Radiologic Technologists, or ARRT, began to consider a certification in mammography for radiologic technologists performing breast imaging. The ARRT began its mammography certification in 1991 as the first postprimary practice examination offered by the organization. This exam helps to ensure that technologists are competent in a clinical area and that they have the foundational knowledge necessary to develop professionally in the field. Today the ARRT examination in mammography consists of 115 multiple choice questions covering patient factors, instrumentation and breast imaging procedures. Candidates must meet very specific requirements to sit for the exam, including clinical experience in mammography procedures, quality control tests, interventional procedures, and radiographic critique and interpretation. Candidates must also meet structured education requirements and the initial requirements of the Mammography Quality Standards Act. Technologists who successfully complete the mammography certification exam and adhere to the ARRT standards of ethics may include an (M) with their ARRT radiography credentials. As of August 2016, there were more than 49,000 mammographers registered by the ARRT. 39. Mammography Quality Standards Act (MQSA)

11 Until 1994, both ACR accreditation and ARRT certification were voluntary, which meant there still was a lack of consistency in mammography quality across the U.S. Although both organizations had worked diligently to establish high standards, some facilities continued to produce images of suboptimal quality with patient doses that exceeded recommendations. Additionally, demand for mammography services increased after Medicare began reimbursing for screening mammography in 1992, and the American Cancer Society began recommending that women have screening mammograms beginning at age 40. To ensure that mammography was performed in a uniform manner across the country and that Medicare funds were used for quality imaging exams, the U.S. Congress passed legislation in 1993 requiring the FDA to create a breast imaging quality inspection program. The Mammography Quality Standards Act, or MQSA, was enacted as Public Law after years of public comment; since its enactment, the law has been amended 3 times. Passage of MQSA marked the first time the federal government regulated a specific medical imaging exam. The regulations became effective in February 1994, and the first MQSA inspection occurred on January 16, 1995, in Fargo, North Dakota. As of August 2016, MQSA reports more than 8,700 accredited mammography facilities. ACR is by far the largest FDA-approved accreditation body in the United States; however several states can certify facilities under MQSA within their state boundaries. Veterans Health Administration facilities are exempt from MQSA requirements. 40. MQSA Personnel Requirements To ensure high-quality, consistent medical imaging within mammography facilities, MQSA established specific guidelines for personnel. A minimum of 3 people should be involved in a facility s mammography program: a mammographer, a radiologist and a medical physicist. Many breast imaging providers contract with a consulting medical physicist to perform the annual review, while a mammographer completes the daily quality control checks. Some larger providers employ a technologist to focus on quality control in the facility; this technologist may be a mammographer or may be certified by the ARRT in quality management. Regardless of a facility s staff mix, the responsibility for quality, accuracy and consistency is shared among everyone who works at the facility. 41. MQSA Requirements for Mammographers Requirements for mammographers are unique in that they currently are the only federal guidelines for medical imaging technologists. Although most states have specific guidelines or licensing requirements for technologists performing medical imaging, the federal government has very limited regulations for medical personnel outside of breast imaging. MQSA requires that mammographers hold a general radiography license in the state where they practice. According to the ASRT, 40 states require licensure for radiographers as of August If a state does not require radiography licensure, the mammographer must be certified to perform radiologic examinations by another FDA-approved body. Secondly, mammographers must complete an initial training requirement of 40 hours of instruction in mammography. The training must be presented by a qualified instructor and may include topics such as positioning, anatomy, quality control, and imaging patients with breast augmentation. The mammographer also must perform 25 mammograms under the direct supervision of a qualified instructor; this may count as 12.5 hours of instruction time toward the 40-hour total. In addition, a minimum of 8 hours of instruction must be completed in each modality the mammographer plans to use. Lastly, mammographers must meet continuing qualifications requirements, including the performance of 200 mammograms every 24 months and the completion of 15 hours of mammography-specific continuing education every 36 months. The 15 mammography-specific credits are not added to the 24-credit requirement for general radiographers; the credit hours may count for both radiography and mammography continuing education requirements. However, at least 6 of the 15 hours must be related to each of the modalities in which a mammographer practices. Mammographers should consult the most recent FDA regulations for modality-specific requirements.

12 42. MQSA Requirements for Radiologists Much like mammographers, radiologists interpreting mammograms must meet licensing, education and continuing qualifications requirements. Radiologists must be licensed to practice in their states. A gray area can exist when digital mammograms are performed in one state and interpreted in another, such as with teleradiology. In these cases the radiologist may be required to have a license in the state where the exam was performed as well as the state in which he or she interprets the study. Secondly, the radiologist must meet specific educational requirements through board certification or through a minimum of 3 months of training in mammography interpretation. In addition, the radiologist must complete 60 hours of medical education specific to mammography, including anatomy, quality control, technique and pathology. He or she must also read 240 mammography exams under the supervision of a qualified radiologist. Radiologists qualified to interpret mammograms must also meet continuing qualifications requirements. The radiologist must interpret a minimum of 960 mammography exams in the 2-year period preceding a facility s MQSA inspection, and he or she must complete 15 category I continuing medical education credits in the 3 years before the facility s MQSA inspection. 43. MQSA Requirements for Medical Physicists MQSA requirements for medical physicists differ only slightly from the licensing, educational and continuing qualifications requirements for mammographers and radiologists. Medical physicists must be licensed in the state where they perform MQSA inspections or hold a specialized certification that allows them to perform physics evaluations of mammography equipment. The medical physicist needs a master s degree or higher in a physical science and a minimum 20 hours of education specific to mammography facility inspections. Additional education requirements include performing a survey of at least 1 mammography facility and 10 total mammography units under the supervision of a qualified medical physicist. Continuing qualifications requirements for medical physicists include completing 15 continuing education hours specific to mammography in the 3 years prior to the facility s annual inspection. The medical physicist also must have surveyed 2 different facilities and at least 6 individual mammography units in the 2 years preceding the facility s annual MQSA inspection. MQSA outlines the specific tests and acceptable limits that are part of the annual survey. 44. Knowledge Check 45. Knowledge Check 46. Screening Mammography Mammography can be divided into 3 major areas: screening mammography, diagnostic mammography, and additional procedures. The majority of mammograms are either screening or diagnostic. Screening mammography refers to imaging that is performed on a person who is asymptomatic, or who shows no signs or symptoms of breast cancer. Its purpose is to detect abnormalities before they become symptomatic and improve the chances of successful treatment. Patients often have the choice of selfreferring, meaning that they begin the screening process on their own, or self-requesting, meaning the patient requests screening mammography from a physician. As of October 2015, the American Cancer Society recommends annual screening mammograms for women between the ages of 45 and 54, and biennial exams for women aged 55 and older. Additionally, women aged 40 to 44 and women 55 and older should have the choice to receive annual screening mammograms. Women with a high risk of breast cancer may begin annual screening mammography

13 earlier, but this is a decision made by the patient in conjunction with her physician. The most important aspect of breast cancer screening is to make every attempt to catch cancer in its early stage. 47. Diagnostic Mammography Diagnostic mammography is the process of using mammographic techniques to evaluate the breast tissue of a patient who displays clinical signs and symptoms, such as a palpable lump or nipple discharge. Diagnostic mammography also may be performed following a screening mammogram if the radiologist reports abnormal or questionable findings. It is not unusual for a patient to complete a screening mammogram and then be called back for a diagnostic mammogram. Although the patient may be understandably worried about returning for another exam, performing a diagnostic mammogram simply evaluates the breast or a certain portion of the breast more closely; it does not confirm cancer. Additional mammography procedures often are used to further evaluate a suspicious mass or calcification following a diagnostic mammogram. These procedures may involve exaggerated projections, magnification, spot compression, or a combination of these procedures. 48. Interventional Procedures Breast biopsy refers to the removal of a portion of suspicious tissue for evaluation of pathological abnormalities. During a stereotactic, or mammographically-guided breast biopsy, the patient either lies prone on a table or sits next to a biopsy machine. After acquiring small, targeted mammographic images to localize the suspected lesion, a needle is placed into the area of interest and a small piece of tissue is removed for further examination by a pathologist. If the lesion is most likely cancerous and the patient, in consultation with her physician, has determined to have it removed surgically, needle localization mammography may be required. Because cancerous and normal breast tissues have many of the same attributes, it is sometimes difficult for the surgeon to know if the tissue being removed is cancerous or normal. In this case, preoperative needle localization is performed in much the same way as a breast biopsy. With localization mammography, however, the radiologist places a small wire in the middle of the lesion to act as a target for the surgeon. Excision of the localization wire and the surrounding tissue ensures removal of the pathology. This is often validated by sending the tissue specimen to the imaging department for radiographic evaluation; if the lesion is seen in the specimen, there is a high probability that the appropriate tissue has been removed. A pathologist will then evaluate the specimen to determine if it is cancerous. 49. Digital Breast Tomosynthesis (DBT) Digital breast tomosynthesis, or DBT, is a relatively new imaging modality. DBT technology improves the detection and characterization of breast abnormalities because it subtracts overlapping structures from the image of the breast. It can be used for both screening and diagnostic mammography exams. Digital breast tomosynthesis was first approved by the FDA in 2011, and currently there are three FDAapproved DBT systems. The DBT unit is similar in appearance to a conventional mammography unit, but in tomosynthesis, the tube moves in an arc over the breast to acquire multiple quick, low-dose images from different angles. Specialized computer software allows these images to be reconstructed into the form of a three-dimensional breast, in the same way reconstructed CT images are produced. The images are displayed as a collection of slices, which increases the capability of the radiologist to see small abnormalities in the breast that may have been superimposed with other breast structures on a standard mammogram. The total radiation exposure from a tomosynthesis exam is roughly equal to that of a single conventional mammogram. 50. Breast Ultrasound Imaging It s important to understand that mammography is only 1 modality within the scope of breast imaging; new technologies have created a wide range of breast imaging possibilities.

14 Ultrasound imaging of the breast often is performed in conjunction with diagnostic mammography to further evaluate areas of concern. Ultrasound is especially useful in determining whether a lesion is a solid mass or a fluid-filled cyst, and it also can be used to guide interventional procedures of the breast, including biopsy, aspiration and localization. Additionally, automated breast ultrasound was approved by the FDA in 2012 as an adjunct to screening mammography for patients with dense breasts. An advantage of using ultrasound, when possible, is the absence of ionizing radiation exposure. 51. Breast-Specific Gamma Imaging (BSGI) Molecular imaging is beginning to play a role in the detection of certain types of breast cancer. The technique, called breast-specific gamma imaging or BSGI, uses a radiotracer to detect cancer cells. Because cancerous cells metabolize the radiotracer faster than healthy cells, the resulting images show areas of concern called hot spots. Hot spots appear darker than normal tissue. BSGI seems to be especially effective in identifying new areas of cancer cell growth in patients with a known breast cancer detected by mammography. The technique also seems to be useful for women with dense breast tissue that is difficult to image with radiographic equipment. 52. Breast MR Breast MR produces images with the high resolution and high contrast required of breast imaging, and it can demonstrate nearly all of the cancers that may occur in the breast. However, there are some challenges associated with the modality, such as high false-positive rates. Breast MR is more expensive than mammography, and it is susceptible to positioning errors and patient motion artifacts. Despite these drawbacks, the use of breast MR is promising for some patients because of the high quality of images and the lack of radiation exposure. According to the ACR, breast MR is indicated as a screening modality for patients with a high risk of breast cancer and for patients with breast augmentation. It also is used to screen the contralateral breast in patients recently diagnosed with a malignancy, and it helps in evaluating the extent of disease or response to therapy for those whose cancer already has been diagnosed. Specific coils have been developed for use in breast MR imaging. The patient lies prone on the MR table with the breast tissue positioned inside the coils below her. Gadolinium contrast is injected into the patient to enhance breast anatomy. 53. Breast Mammography Radiographic breast mammography remains the gold standard in breast imaging today. Despite the radiation exposure associated with mammography, the high-quality images produced have no doubt saved countless lives. When the equipment is used by a properly educated mammographer and the images are interpreted by a credentialed radiologist, mammography has the potential to save and improve the lives of thousands of patients. 54. Knowledge Check 55. Knowledge Check 56. Conclusion This concludes Breast Imaging Essentials: Module 1 Fundamentals of Breast Imaging. You should now be able to: Discuss radiographic principles and how they apply to mammographic imaging. List technical factors and techniques that produce quality mammographic images while keeping patient radiation exposure to a minimum. Explain the development and purpose of digital mammography. Explain the purpose of regulations and licensing regarding performance of mammography. List additional breast imaging modalities. 57. References