body of the abstract

Diffusion-weighted MR imaging (DW MRI) is a rapid MRI technique that does not require administration of a contrast agent and may have a role as an alternative to contrast-enhanced MRI for breast cancer screening. DW MRI measures the mobility of water molecules within tissue. On DW MRI, breast cancers typically exhibit restricted diffusion, attributed to increased cellular density and reduced extracellular space, and appear hyperintense to surrounding tissues with lower apparent diffusion coefficient (ADC) values. Based on this characteristic, DW MRI may offer a viable non-contrast method to detect breast cancer without the costs and toxicity associated with dynamic contrast-enhanced MRI (DCE-MRI). This application of DW MRI has not yet been widely explored but is particularly timely given growing health concerns related to the long-term use of gadolinium contrast agents utilized in conventional breast MRI for high-risk screening. Moreover, increasing breast density legislation is raising awareness of the limitations of mammography in women with dense breasts, emphasizing the need for additional cost-effective supplemental screening options in this population. Preliminary studies suggest DW MRI may provide higher sensitivity than screening mammography and ultrasound for detection of breast malignancies, without the costs and toxicity of DCE-MRI. In the field of cancer detection, current evidence suggests that DW MRI combined with nonenhanced T1- and T2-weighted sequences provides a higher sensitivity than mammography or mammography combined with ultrasound but lower sensitivity than DCE MRI. However, advances in DW MRI acquisition, post-processing, and standardized interpretation may have significantly improved DW MRI performance in breast cancer detection. Technical innovations to optimize image quality warrant further investigation to increase the sensitivity of DW MRI. Steps to consider when implementing an unenhanced MRI program include protocol selection and execution, scheduling, and billing. Since there is no standardized protocol, one of the first steps to introducing an unenhanced MRI program is determining and implementing a protocol. An unenhanced breast MRI protocol included an anatomical T1-weighted sequence and a DW sequence with b-values of 0, 800, and 1200 s/mm. The T2-weighted sequence was not acquired because the DW MRI b=0 images provide nearly identical T2-weighted weighted image contrast. The unenhanced protocol takes about 10 minutes compared to 35 minutes for a full standard protocol. Adjusting the MRI scheduling templates to accommodate the 15-minute unenhanced MRI exam is helpful and enables efficient throughput compared to the standard 40-minute MRI exam. With the shorter examination period, four unenhanced MRI exams can be performed per hour. The development and success of an unenhanced breast MRI program require collaboration and communication between the breast radiologists and the staff and stakeholders from multiple sites. Quality control for unenhanced MRI should include appropriate protocols for image acquisition and image interpretation, as well as for the management of lesions identified by unenhanced MRI. As the unenhanced MRI program is incorporated into clinical practice, auditing routine screening outcomes quarterly is critical for the program's continued success. In addition, DW MRI has a shorter scan time and does not require intravenous contrast materials, which could increase the availability and cost-effectiveness of breast MRI scans and enable a faster throughput. The technique has potential to benefit high-risk women with contraindications to gadolinium-based contrast agents, but indications may be expanded to women of intermediate risk factors such as personal history of breast cancer or dense breast tissue. The results of ongoing prospective clinical trials are expected to provide the evidence necessary to implement DW MRI as a stand-alone modality in a diverse patient population. Finally, larger prospective and multicenter trials are needed to validate single study findings and assess the performance of DW MRI for generalized breast cancer screening.

Acknowledgements

I thank Woo Kyung Moon, Nita Amornsiripanitch, and Savannah Partridge in preparing this lecture.