BI-RADS in general and the lexicon specifically were not intended to be static [6
]. After the initial creation of BI-RADS in 1993 [21
], 3 more editions were created in 1995 [22
], 1998 [23
], and 2003 [24
]. However, the path to a successfully adopted breast imaging lexicon was not always smooth. Controversy involving the BI-RADS lexicon arose in 1994 with the publication of an editorial in which the author contested that “expertise is the heart of the problem, not terminology. BI-RADS, with its emphasis on words and definitions, is barking up the wrong tree” [25
]. The authors of the BI-RADS lexicon responded in a follow-up editorial that addressed many concerns that were being voiced by the community. In particular, the response clarified that the BI-RADS lexicon was intended to be a tool that radiologists would use to communicate with clinicians to convey concise and orderly descriptions of findings in understandable, standardized language, which in turn contributes to an orderly thought process and logical assessments and recommendations. Furthermore, BI-RADS was designed to encourage improvements in expertise because it provided standardized recommendations that could be used for performance tracking: “Without standardized terms to describe important features … there is no means of obtaining objective data to improve. Indeed, this format is important for all reports we generate, not only mammography” [26
]. This thoughtful and productive debate strengthened support for the lexicon.
Each BI-RADS revision added components that were important for clarification, management, or quality assurance. The third edition of BI-RADS incorporated an atlas that provided an artist’s renderings of examples of each descriptor. The fourth edition made several changes in lexicon terminology [27
]. To decrease confusion between terminology for overall breast density and the descriptor density
(referring to a noncalcified finding seen on only one of the two standard mammographic views), the authors adopted the descriptor term asymmetry
in place of density
. To parallel this change in terminology, asymmetric breast tissue
was renamed global asymmetry
(a nonmass finding seen on at least two views that occupies at least a quadrant), and focal asymmetric density
was renamed focal asymmetry
(a nonmass finding seen on at least two views that occupies less than a quadrant). Furthermore, a study demonstrating that amorphous microcalcifications carried a 20% risk for malignancy [28
] prompted the BI-RADS Committee to subcategorize suspicious microcalcification descriptors into “intermediate risk” (including the amorphous descriptor) and “higher probability of malignancy.” Additional published data related to microcalcification descriptors demonstrated that the pleomorphic
descriptor was not stratifying risk beyond the overall risk for suspicious microcalcifications [29
]. In response, the BI-RADS Committee divided “pleomorphic” microcalcifications into two more specific categories: “coarse heterogeneous” and “fine pleomorphic.” This distinction was subsequently shown to effectively stratify the probability of malignancy among these types of calcifications [30
]. To further help with risk stratification, the fourth edition provided the option to subdivide BI-RADS assessment category 4 into 4A (low suspicion for malignancy), 4B (intermediate suspicion for malignancy), and 4C (moderate concern but not classic for malignancy). These subdivisions provide assessment and reporting options designed to help both physicians and patients understand likely biopsy findings and probable follow-up recommendations [27
The development of a breast ultrasound lexicon, BI-RADS–Ultrasound, first published as part of the fourth edition of BI-RADS, demonstrated similar themes. In 1998, the ACR received a grant from the Office on Women’s Health of the US Department of Health and Human Services to support protocol development for research in breast ultrasound (contract 282-97-0076, Federal Technology Transfer Program to Advance Novel Breast Imaging Technologies, US Public Health Service, Office on Women’s Health, Department of Health and Human Services). An ACR expert working group of national and international breast imagers with special interest in breast ultrasound met in Maine to design research projects that might advance use of ultrasound in conjunction with mammography and other imaging modalities. These potential studies included 1) the identification of criteria to differentiate benign from malignant solid masses, 2) ultrasound for breast cancer screening, and 3) using ultrasound to guide diagnostic interventions and as a therapeutic agent (high-frequency ultrasound). Until that time, ultrasound was used primarily for cyst-solid differentiation, despite FDA premarket approval of Advanced Technology Laboratories’ (Bothell, Washington; now Philips Medical Systems, Andover, Massachusetts) “high-definition imaging” in 1996. This approval was based on an international, multicenter study involving ultrasound evaluation of nearly 1,000 breast lesions (published as a monograph by Advanced Technology Laboratories rather than in the peer-reviewed literature), which indicated that ultrasound improved specificity for masses found to be indeterminate on mammography and physical examination. This study asserted the need for additional research in defining diagnostic criteria for classifying solid breast masses on ultrasound.
The ACR expert working group proposed a standardized lexicon, similar to BI-RADS for mammography, to provide a foundation for research characterizing solid masses for risk stratification and evidence-based management. For example, this strictly defined lexicon could be used to determine benign and probably benign masses. Soon after the Maine meeting, a subcommittee of the ACR’s BI-RADS Committee was formed to officially develop BI-RADS–Ultrasound. After several iterations, the consensus document was presented and tested at select subspecialty meetings, including the Society of Breast Imaging’s biennial meeting in San Diego in 2001. The descriptors and assessment categories were validated by statistical analysis of interobserver consistency (κ
), showing good agreement for most terms among the experienced and novice breast imaging participants [31
BI-RADS–Ultrasound was predicated on high-quality images and real-time ultrasound observations and encourages the assessment of combined features. Using descriptors from several feature categories can balance the risk associated with all relevant features, but usually, the most suspicious feature will dominate the final assessment and recommendation [32
]. Validation of the grouping of features is derived from univariate, bivariate, and multivariate analyses of features characterizing the lesions submitted as evidence for FDA premarket approval by Advanced Technology Laboratories for its high-definition imaging system. Groups of features were also used in the development of the mass classification algorithm proposed by Stavros et al [33
]. For BI-RADS–Ultrasound, the three most important feature categories, taken together are shape, margin, and orientation, the last a feature unique to ultrasound.
BI-RADS–Ultrasound can also contribute to the investigation of emerging technologies. Computer-assisted diagnosis programs use segmentation and feature extraction to classify breast masses on the basis of features similar to BI-RADS–Ultrasound. Structured reporting, rapidly evolving and currently available in breast imaging reporting software packages initially designed for mammography, uses BI-RADS-Ultrasound to construct standardized reports and encourage consistent communication.
The development of BI-RADS–Ultrasound that began more than a decade ago will continue. New feature categories (eg, elasticity) will require standardization, evidence, and validation. The continuing goals for BI-RADS of providing useful, comprehensive guides to breast imagers for analyzing, assessing, reporting, and managing breast lesions is especially critical for breast ultrasound, which has long been considered an operator-dependent modality.
The fourth edition of BI-RADS also incorporated breast MRI descriptors. Between the early 1970s and the late 1990s, contrast-enhanced breast MRI had shown great promise. Studies demonstrated near 100% sensitivity for detecting early invasive breast cancer, though these results were tempered by more modest specificity [34
]. However, attempts to systematically evaluate the literature were stymied by nonuniform approaches to image acquisition and reporting. Variable magnet field strength, hardware, pulse sequences, and lesion characterization (including both morphologic and kinetic data) led to freedom of innovation but also impeded consensus development. A Web-based survey of the members of the Society of Breast Imaging conducted from September 2006 to January 2007 showed that poorly standardized breast MRI protocols were a serious problem [35
]. Of 551 responding facilities, 84% indicated they never or rarely would interpret contrast-enhanced breast MRI examinations performed at other facilities because of protocol variability.
Recognizing a clear need to achieve consensus on MRI acquisition techniques and lesion terminology, the Public Health Service’s Office on Women’s Health funded the International Working Group for Breast MRI in 1997. This group’s goal was to disseminate evidence-based consensus on the performance and interpretation of breast MRI. A subset of the international working group, the Lesion Diagnosis Working Group, composed of internationally recognized breast MRI investigators, was charged with developing a standardized breast MRI lexicon and reporting system [36
]. This group later became the Subcommittee on MRI Lexicon Breast Cancer.
In 1998, the Lesion Diagnosis Working Group developed minimum reporting standards on MRI scanning techniques, region-of-interest kinetic curve acquisition, lesion architecture, and kinetic curve interpretation. These experts used the breast MRI literature to compile the most important descriptors for lesion diagnosis that would prompt specific patient management recommendations, such as biopsy. The morphologic descriptors were based on terms used in the BI-RADS mammography lexicon, when appropriate, to facilitate use and adoption in clinical practice. After the development of the preliminary breast MRI lexicon, this group performed several reader studies (funded by the National Cancer Institute, the Susan G. Komen Breast Cancer Foundation, and the ACR) to evaluate the reproducibility of these descriptors for the characterization of biopsy-proven MRI abnormalities [37
]. Using the results of each study, portions of the lexicon were expanded and others eliminated in a stepwise, progressive manner.
Optimization and testing of the lexicon continued for a period of 6 years, resulting in BI-RADS–MRI, first published in the fourth edition of BI-RADS in 2003 [24
]. The breast MRI lexicon is now widely used for breast MRI reporting, teaching, research, and communication. However, the work of the Subcommittee on MRI Lexicon Breast Cancer, researchers, and practitioners is far from over; the accuracy and reproducibility of the lexicon continue to be tested in the clinical and scientific arenas [38
], and novel features and techniques are emerging rapidly. For example, the importance of background enhancement, the use of T2-weighted sequences, and bilateral scanning [42
] prompted the committee to recommend the routine use of these techniques. Major advances in hardware, software, magnet field strength, and pulse sequence development, including parallel imaging, diffusion-weighted imaging, and MR spectroscopy, among other advances, promise to contribute to improved diagnostic capability as well as add complexity to the lexicon [45
]. For example, the increased use of computer-aided diagnosis has led to major changes in breast MRI interpretation [35
]. Furthermore, MRI-guided biopsy provides tissue diagnosis for abnormalities seen only on MRI, enabling early breast cancer diagnosis as well as the collection and calculation of accurate performance metrics. In fact, the ACR’s MRI Lexicon Committee is planning a new edition for 2010 that will clarify existing descriptors, eliminate descriptors that did not work in clinical practice, and add T2 weighting, background enhancement, and breast implant descriptions. Clearly, the BI-RADS–MRI is an evolving document that requires continued development to provide up-to-date, evidence-based standard terminology for its continued contribution to improving the accuracy of breast MRI. Technological progress, the multimodality evolution of breast imaging, and maintenance of the data-driven lexicon will serve as the foundation of the fifth edition of BI-RADS, which will include the second editions of BI-RADS–Ultrasound and BI-RADS–MRI.
There also have been spinoffs from BI-RADS, including the National Mammography Database (NMD) initiative [46
]. The ACR originally launched the NMD in 1999 but subsequently put the initiative on hold in 2002 because of limited resources. However, in 2007, the ACR began the development of the National Radiology Data Registry, a data warehouse to collect quality improvement data across multiple modalities. The NMD is one of the registries within the National Radiology Data Registry. BI-RADS licensed software vendors are required to comply with NMD requirements, enabling the automatic upload of facility audit data directly to the ACR. During the second half of 2009, the ACR pilot-tested the NMD in early 2009 and opened NMD reporting to interested participants in the summer of 2009. The ACR will provide outcomes reports to participants to enable comparison with national benchmarks as well as practices similar in size, type, and region.