Synopsis

Keywords: Body: Breast

The need for breast MRI is expanding to include its role as a screening method and as an adjunct to personalized and minimally invasive treatment. The next BI-RADS 6th edition will include several additional non-contrast MR methods, which can complement dynamic contrast-enhanced MRI to more accurately evaluate breast lesions and address expanding clinical needs. This talk will focus on the standard dynamic contrast-enhanced MRI as well as non-contrast sequences that will be published in BI-RADS 6^th edition to take advantage of the new edition.

BI-RADS

BI-RADS, which is used around the world as a textbook for breast imaging, added a section on MRI in its fourth edition in 2003, and was updated to its fifth edition in 2013. A sixth edition will be published this year. The BI-RADS lexicon provides standardized acquisition and reporting for breast lesions, which is the common language of radiologists worldwide and also serves as a bridge between breast surgeons and radiologists. BI-RADS evaluation consists of two pillars, morphology and kinetics. Though washout kinetics may be the most popular descriptor among radiologists, it is important to recognize that kinetics alone cannot determine whether a lesion is benign or malignant. Final categorization stratified by the likelihood of malignancy is decided by radiologists based on the combination of descriptors, but several studies have examined the malignancy rate for each descriptor or combination of them (1). There are some studies suggesting the decision rules partially using the BI-RADS lexicon in an evidence-based score (e.g. Kaiser Score) (2). These approaches may allow for more accurate categorization, with or without experience.

Non-contrast MRI

Non-contrast sequences can complement dynamic contrast-enhanced (DCE) MRI for a more accurate evaluation of breast MRI. In particular, T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) are going to be referred to in the BI-RADS sixth edition.Edema cannot be evaluated in the DCE sequences but is evident in T2WI. Focal breast edema is usually associated with malignancy. It is classified into three types: peritumoral, subcutaneous, and pre-pectoral edema, each of which may have a different etiology (3). The T2WI-high signal inside a lesion has several meanings. In cases of round or oval mass lesions with circumscribed margins, the T2WI-high signal increases confidence in benignity, indicating typical fibroadenoma. A mass with smooth, thin rim enhancement with central T1 and/or T2 hyperintensity is compatible with pericystic inflammation (1). On the other hand, there are some types of breast cancer exhibiting T2WI-high signal such as mucinous carcinoma and necrotic areas typically in triple-negative breast cancer. DWI allows for both qualitative and quantitative evaluation of breast lesions (4). It is considered an important complementary imaging modality to DCE MRI, especially in terms of specificity and to avoid unnecessary biopsies.T1-weighted imaging (T1WI) without fat suppression is sometimes useful in diagnosing rare benign lesions, such as hamartoma and fat necrosis. It also helps to diagnose thoracic invasion of breast cancer.Clips and markers placed in the breast are easily detected on T2WI or T1WI without fat suppression and are sometimes useful in the evaluation of treatment response or recurrence.

Future roles of breast MRI

Future direction for the management of breast may consist of ① risk-stratified and personalized screening, ② image-based tumor classification, and ③ personalized and minimally-invasive treatment, all of which are closely related to diagnostic imaging. The need for breast MRI as screening is expanding, and is now recommended for high-risk women in some countries. Background parenchymal enhancement may be used as a predictor for future breast cancer risk (5). Evaluation of treatment response during and after neoadjuvant systemic therapy is one of the important roles of breast MRI. There is an attempt to omit resection if a complete response is achieved after systemic therapy, and accurate prediction of complete response is desired.

Acknowledgements

I thank Masako Kataoka, MD, PhD, and Mami Iima, MD, PhD, for providing valuable advice on this presentation.