Synopsis

Keywords: Body: Breast

Diffusion MRI has emerged as an alternative and complementary technology for breast evaluation. It has already shown the clinical value of diffusion MRI for improving specificity leading to a decreased benign biopsy for suspicious lesions on contrast-enhanced breast MRI. In addition, studies are actively underway to evaluate its value as a stand-alone screening method. To help radiologists implement DWI in clinical practice and to inspire physicists to develop new technologies, this lecture will outline principles, standardized techniques, clinical applications, and research of diffusion MRI using ADC. Furthermore, advanced DWI techniques, including IVIM, DKI, and DTI, will be briefly reviewed.

Dynamic contrast-enhanced (DCE)-MRI of the breast has been the standard MRI technique for breast imaging. However, it requires administration of intravenous contrast agent, and long term safety of accumulation of gadolinium has not yet been proven. In this context, diffusion-weighted MRI (DWI) has emerged as an alternative and complementary technology for breast evaluation. The usage of DWI has been limited for the last two decades due to considerable artifacts and noise. However, due to technological advances, improvements in standardized image acquisition, and optimization of image quality or interpretations, DWI using apparent diffusion coefficient (ADC) has now achieved several clinical applications.
ADC quantifies mean bulk diffusion per pixel and is an established quantitative surrogate for tissue cellularity and structural features. Quantitative ADC can be used to downgrade suspicious lesions on contrast-enhanced MRI to reduce unnecessary biopsy. In the multicenter trials, 21% to 33% of unnecessary biopsy could be avoided based on DWI. In addition, DWI was found to be less sensitive to cancer detection than DCE-MRI, but DWI’s sensitivity was found to be superior to mammography or ultrasound. The cancer detection rate comparable to abbreviated MRI has been reported in one study. Thus, several prospective multicenter trials are underway to compare performance of DWI alone vs. DCE-MRI or other combinations of mammography or US for high to intermediate risk women. Stand-alone DWI screening is expected to be a valuable alternative for women of contraindications to contrast agents or intermediate-risk women.
Many studies have also demonstrated the ability of DWI using ADC, intravoxel incoherent motion (IVIM), non-Gaussian kurtosis imaging (DKI), and diffusion tensor imaging (DTI) in the characterization of breast tumors, prediction of molecular subtypes or responsiveness of neoadjuvant chemotherapy or as indicators of tumor aggressiveness or invasiveness of tumors. In the literature, significant correlations have been reported between various DWI parameters and breast cancer molecular subtype, invasive cancer (compared with in situ cancers), tumor grade, Ki-67 level, or lymphovascular invasion. In addition, the association between pretreatment ADC or changes in ADC and tumor response or pCR has also been extensively studied. However, various results have been reported depending on the MRI timing, imaging parameter measurement methods such as histogram analysis, advanced DWI modeling approaches, or definitions of responsiveness. With respect to advanced DWI techniques, IVIM, non-Gaussian DWI, and DTI metrics provide additional insights into breast pathophysiology, but they are still a field of research due to the lack of standardization of image acquisition and contradictory results.
In conclusion, the clinical value of DWI in breast is promising and has not yet been fully investigated.

Acknowledgements

No acknowledgement found.