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Interpreting tomosynthesis screening exams differs from interpreting two-dimensional (2D) digital images. Just as switching from film-screen image interpretation using a view box with a magnifying glass to manipulating digital images on computer monitors, tomosynthesis similarly requires developing a different pattern of observation and assessment. Much more information is packed into a tomosynthesis exam compared with 2D full-field digital mammography, requiring more to observe and mentally assimilate by the radiologist. This process involves assessment of numerous individual images and requires scrolling back and forth multiple times to fully assess all parts of the breast and sometimes additionally through focal areas (targeted scrolling) in order to best evaluate potentially concerning abnormalities.
Increased time required to read tomosynthesis exams compared to 2D mammography has been shown by several studies. Batch reading of screening exams has been the most cost-effective method to read 2D analog exams mostly due to the labor and time required to load and take down analog films on an alternator, making it impractical to read screening cases online (ie, giving patients immediate results before leaving the breast imaging facility as is the usual practice following a diagnostic exam). Even in the early years during the transition from analog to digital mammography, batch reading was still very practical because prior analog images were still needed for comparison purposes. However, once a practice has achieved a state whereby the current and recent priors are all digital, reading online becomes feasible. With tomosynthesis mammography there are reduced screening recalls and fewer diagnostic mammograms requiring short interval follow-ups (Breast Imaging Reporting and Data System 3 [BI-RADS 3]). In addition, diagnostic work-ups with tomosynthesis are also greatly abbreviated, requiring fewer mammographic images. All of these factors combine so that over time breast imaging practices may find that radiologists actually have more time and can read screening cases online. Thus, although individual tomosynthesis exams may take a little more time to view and interpret, overall the caseload and workflow are improved and more efficient for both radiologists and patients.
Just as with the apprehension associated with the transition from film to digital mammography, once the process of reading tomosynthesis exams becomes familiar, the increased time and effort may be normalized to the point that interpreting cases without tomosynthesis views seems far too abbreviated and incomplete. While nothing can compare with the confidence associated with firsthand tomosynthesis interpretive experience, there are some tips that may expedite this process.
Reading any mammogram requires complete undivided attention, but reading tomosynthesis cases requires the brain to take in and process more information than it is used to. Reading a large number of consecutive screening tomosynthesis exams can potentially be more tiring than reading a similar number of 2D cases. Every mammogram belongs to a patient who has made time out of her daily life to come for the exam, as well as endured potentially uncomfortable positioning and radiation exposure. Women choose mammography because they want to have the best chance of detecting breast cancer early. Distractions are common in busy practices, but attempts must be made to minimize such diversions because important findings may otherwise be missed. When proceeding through the hanging protocol of any particular mammogram, try to avoid interruptions. Potentially concerning areas on the mammogram that the brain may be processing, consciously or subconsciously, will be lost if your attention is drawn away from the images. Ask your staff or colleagues to try not to interrupt you in the middle of a case. If interrupted, start over . Otherwise you’ll risk missing something. While many mammograms may be read on any particular day, each mammogram is connected to a different individual and each one deserves the utmost careful consideration by the radiologist. If you are fatigued, step away and take a break.
Ease of viewing tomosynthesis exams is extremely important. Analogous to driving a car, it is best if you can keep your eyes on the images, and not look down at buttons, keyboards, and so on ( Fig. 7.1 ). Having a well-designed keypad and hanging protocol that permits simple single button advancement of images and toggling between 2D and tomosynthesis not only makes the viewing process quicker and more streamlined, it also prevents losing track of findings being mentally processed. A hanging protocol can be developed such that a single button can advance through all images of a screening exam—including 2D, full resolution images, 3D with priors, and computer-aided detection—eliminating the need to take one’s eyes off the monitor. Propriety workstations have such optimized keypads, but some picture archiving and communication system (PACS) vendors also supply these features. It is strongly recommended to establish such an optimal workstation configuration, ultimately saving time and potentially reducing errors.
Tomosynthesis interpretation obviously involves scrolling! Each mammographic view has many thin slices to analyze—the exact number depends on the breast thickness. To fully assess all slices within a particular view and not miss any part of the breast, it is necessary to scroll back and forth through the image multiple times. Develop a routine and consistent process of inspecting each section of the breast such that no part is missed. At a minimum, one must scroll through a normal-sized breast three times (eg, upper or outer, middle, and lower or inner). While the tomosynthesis slice images can be reviewed in automatic cine mode, it is better to be in control—similar to driving—such that when a potential lesion catches your eye, you can hover over it (targeted scrolling) to more closely evaluate the region. For many radiologists, the most simple and ergonomic method of scrolling is by depressing the scroll wheel on the mouse and slowly moving the entire mouse forward and backward. This requires no wrist or finger movement and only minimal elbow and shoulder motion. Make sure your workspace is not cluttered or cramped and you have ample space for excursion of the mouse.
An important tip with tomosynthesis interpretation is not to mentally assess too many findings simultaneously. For instance, calcifications should be assessed on the full resolution views, while soft tissues and architecture should be assessed separately particularly when scrolling through the tomosynthesis slices. Do not try to do both at once. Also, because there are more images on a tomosynthesis exam compared to conventional 2D mammography, one should be more cautious to avoid missing a lesion due to “satisfaction of search” ( Fig. 7.2 ). If an obvious finding such as a cyst is seen, consciously disregard it at first and look at other areas before going back to more carefully assess the most obvious finding.
When analyzing multiple findings on tomosynthesis, do not try to evaluate them all at once. Each finding should be analyzed on its own, requiring scrolling through the tomosynthesis images multiple times.
When carefully looking for calcifications or scrolling through the stack of images in a tomosynthesis exam, focusing on the “close-up” imaging findings is easy to do. It is, however, very important to take an “arm’s length” view, either at the beginning or end (or both) of the hanging protocol, comparing one breast to the other and each view to prior exams, to assess for more subtle findings such as developing asymmetries. Often such findings can be small and subtle, but even large areas can easily be overlooked when so much of the focus is on the improved detailed imaging tomosynthesis provides ( Fig. 7.3 ). As with reading 2D mammograms, assessing for subtle changes over time is essential for detection of early malignancies. A developing asymmetry is one that appears as a focal area of tissue that is new, larger, or denser compared to prior exams. These findings are usually initially recognized on 2D mammography, and then further scrutinized on the tomosynthesis images. This finding should always be given careful consideration, particularly in postmenopausal women. While most cancers will appear more spiculated or distorted on tomosynthesis images than on 2D, some cancers will present only as a new subtle focal irregular asymmetry or mass even on tomosynthesis and still require recall for a diagnostic work-up. ( Fig. 7.4 ). A negative ultrasound can reassure that a developing asymmetry likely represents an island of normal glandular tissue, and in these cases, routine imaging is usually appropriate, whereas a focal corresponding sonographic finding will help dictate further management such as short-term follow-up or biopsy.
Look for areas of developing asymmetries on the 2D images. Assessment of the big picture is necessary to detect subtle mammographic changes over time. Once a finding is questioned, scrutinize it more carefully by scrolling through the area on the tomosynthesis images to determine if it is real or simply superimposed tissue.
A common concern among new adopters of tomosynthesis is whether review of previous tomosynthesis images is necessary when comparing the current study to the prior year’s exams. While individuals will develop their own personal protocols and preferences over time, generally routine review of prior tomosynthesis exams is not always necessary. Comparison of the prior 2D images usually suffices; however, if questionable areas are noted on the current exam, scrolling through the prior tomosynthesis images is greatly beneficial to either establish stability or recognize the finding as new or changing.
The source projection images should be available for review on the workstation. These are similar to a maximum intensity projection image in magnetic resonance imaging (MRI) and can provide a quick overview of the composition and arrangement of the breast tissue ( Fig. 7.5 ). Most radiologists do not routinely review projection images. However, if there is a question of motion on a particular case, reviewing the projection images may show jumping of the images due to the patient’s breathing or other movement during the tomosynthesis image acquisition. Additionally, if there is an area of questionable findings on the tomosynthesis slice images, review of the projection images—particularly by rotating back and forth—may sometimes help determine if a focal area represents normal fibroglandular tissue or a more concerning finding.
One key tomosynthesis tool is the localization feature. As the radiologist scrolls through the breast image, a localizer tab also moves indicating position within the breast. Additionally, the individual slices are numbered for ease of reviewing or reproducing findings ( Fig. 7.6 ). For example, when scrolling through a craniocaudal (CC) view, the localizer tab moves from the inferior aspect to superior aspect and vice versa. If the radiologist were to stop at any point on the CC view, a look at the localizer tab will indicate that the potential finding lies in the inferior or superior breast, allowing a more targeted inspection of the mediolateral oblique (MLO) view. Assessing the orthogonal location of a lesion initially discovered on the MLO view is slightly more challenging than those initially seen on the CC view as the images proceed from lower outer through to upper inner quadrant, not strictly lateral to medial, as in a true 90-degree view. Furthermore, the angle of projection, while commonly 45 degrees, varies between patients and even within the same patient from year to year. Geometry and projection angle must be kept in mind to be able to mentally map findings in the MLO view to the correct portion of the breast. A visual reminder of MLO positioning demonstrates how some of the lower outer breast projects above the nipple on the early slices in the stack (ie, near the receptor) and tissue in the upper inner breast can project below the nipple on the slices near the compression paddle ( Fig. 7.7 ).
The accurate use of localization is a critical skill in tomosynthesis interpretation. Assessing potential lesions in both projections is much more comprehensive than on 2D mammography alone. The careful targeted scrolling through a new focal area in both projections helps determine whether a true lesion likely exists and requires further evaluation or is not real, therefore precluding recall. The greatest benefit in reducing unnecessary recalls is in the careful assessment of images in both projections and trusting the tomosynthesis images. Areas of focal density may stand out on the 2D images, yet the tomosynthesis slices show it is simply superimposed tissue with no focal correlate in the other projection. Radiologists have varying changes in their recall rates with tomosynthesis, depending on how well they integrate the information in the tomosynthesis images or whether they are still swayed by findings in 2D ( Fig. 7.8 ). Review of diagnostic results of recalled tomosynthesis screening cases is strongly encouraged so that one can better gauge what represents true findings. This exercise can also help the radiologist achieve an appropriate threshold for recall.
The use of tomosynthesis in both the CC and MLO projections is important in order to reap the full benefit of tomosynthesis. While the MLO view may capture more of the breast tissue than the CC view, the CC view produces better separation of tissue and is more uniform from year to year, enabling a more accurate assessment of changing tissue patterns. The CC view also contributes more to precise lesion localization. There is evidence that a greater proportion of suspicious lesions are detected on the CC than the MLO view, making the CC view essential to tomosynthesis assessment. The benefit of performing tomosynthesis only in the MLO view is the reduction in overall radiation exposure; however, there is a risk of losing important diagnostic information.
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