DWI in the Assessment of Breast Lesions

Abstract

Diffusion-weighted imaging (DWI) holds promise to address some of the shortcomings of routine clinical breast magnetic resonance imaging (MRI) and to expand the capabilities of imaging in breast cancer management. DWI reflects tissue microstructure, and provides unique information to aid in characterization of breast lesions. Potential benefits under investigation include improving diagnostic accuracy and guiding treatment decisions. As a result, DWI is increasingly being incorporated into breast MRI protocols and multicenter trials are underway to validate single-institution findings and to establish clinical guidelines. Advancements in DWI acquisition and modeling approaches are helping to improve image quality and extract additional biologic information from breast DWI scans, which may extend diagnostic and prognostic value.

Figure 1

Example breast DWI images obtained in a 37 year old woman with invasive breast cancer. Shown are corresponding images from (A) post-contrast T1-weighted image, (B) DWI S₀ with b = 0 s/mm² (primarily T2-weighted), (C) DWI S_D with b = 1000 s/mm², (D) apparent diffusion coefficient (ADC) map. Invasive lobular carcinoma (arrow) exhibits reduced diffusivity on DW imaging, appearing hyperintense on the S_D image and hypointense on the ADC map.

Figure 2

Examples of benign and malignant breast lesions. (top row) 24 mm invasive ductal carcinoma in a 52 year old woman. (bottom row) 12 mm benign fibroadenoma in a 46 year old woman. Both lesions exhibit enhancement on post-contrast T1-weighted images (A, D) and hyperintensity on diffusion-weighted images (arrows, B, E), but demonstrate marked differences on the ADC maps (C,F), where the malignant lesion (C, arrow) exhibits substantially lower ADC (ADC = 0.70 × 10⁻³ mm²/s) than the fibroadenoma (F, arrow, ADC = 1.81 × 10⁻³mm²/s).

Figure 3

Example of a high-risk lesion (lobular carcinoma in situ) detected in a 54 year-old woman that upgraded to malignancy (ductal carcinoma in situ) on surgical excision. (A) Post-contrast T1-weighted image demonstrates a 67 mm segmental non-mass enhancement (arrow) exhibiting persistent and plateau enhancement that was assessed as BI-RADS category 4. (B) On DWI, the lesion exhibits restricted diffusion with a corresponding dark area on the apparent diffusion coefficient (ADC) map (arrow), with low ADC value measuring 1.13 × 10⁻³ mm²/s. (Adapted from Cheeney S, Rahbar H, Dontchos BN, et al. Apparent diffusion coefficient values may help predict which MRI-detected high-risk breast lesions will upgrade at surgical excision. J Magn Reson Imaging 2017 Feb 9; with permission.)

Figure 4

Therapeutic-induced changes in breast tumor ADC values. MRI images are depicted for non-responding (top row) and responding (bottom row) patients treated for breast cancer. (A) and (E) T1-weighted gadolinium enhanced, (B) and (F): pre-treatment ADC maps, (C) and (G): ADC maps at 8–11 days after treatment initiation, D) and (H): Histograms of ADC values in the tumor pre-treatment and post-treatment initiation. Tumor is delineated from surrounding healthy tissue in the individual images by the purple line. (Reprinted from Galban CJ, Ma B, Malyarenko D, et al. Multi-site clinical evaluation of DW-MRI as a treatment response metric for breast cancer patients undergoing neoadjuvant chemotherapy. PLoS One 2015;10(3):e0122151; with permission.)

Figure 5

Illustration of varying tumor ADC measurement approaches. Shown are (A) Reference T1-weighted post contrast slice, (B) small minimum ADC subregion ROI, mean ADC = 0.65 × 10⁻³ mm²/s, (C) single slice 2D whole tumor ROI, mean ADC = 0.88 × 10⁻³ mm²/s, (D) 3D whole tumor ROI, mean ADC = 1.01 × 10⁻³ mm²/s. As shown, choice of ROI technique can substantially affect lesion ADC measures.

Figure 6

Reduced field-of-view (rFOV) breast DWI technique. Shown are corresponding images (b=0 s/mm²) from (A) standard single shot diffusion-weighted EPI and (B) rFOV diffusion-weighted EPI acquisitions. Imaging resolution (voxel size) for each DWI approach are shown. Compared to standard DWI, rFOV DWI achieves higher spatial resolution and reduces distortions, potentially improving ability to assess lesion morphology as well as diffusivity.

Figure 7

DWI with intravoxel incoherent motion (IVIM) biexponential modeling of an invasive ductal carcinoma in a 62 year old woman. Distinct physiological information is obtained by separating the IVIM components. Shown are the (A) DWI (b=800 × 10⁻³mm²/s) image and maps of the (B) tissue diffusivity (D_t), (C) microvasculature pseudodiffusivity (D_p), and (D) perfusion fraction (f_p), which illustrate reduced diffusion (high cell density) and heterogeneous levels of perfusion within the malignancy.

Figure 8

Example diffusion tensor imaging (DTI) in a 34 year old woman with invasive ductal carcinoma. Shown are (A) Post-contrast T1-weighted subtraction image, (B) ADC map, and (C) fractional anisotropy (FA) map. The enhancing tumor (arrow) exhibits restricted diffusion with reduced ADC (ADC = 0.94 × 10⁻³ mm²/s) and anisotropy (FA = 0.12) versus nearby normal parenchyma, suggesting increased cell density and loss of structured organization.