Diffusion-Weighted Magnetic Resonance Imaging of the Breast: Standardization of Image Acquisition and Interpretation

Abstract

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is a rapid, unenhanced imaging technique that measures the motion of water molecules within tissues and provides information regarding the cell density and tissue microstructure. DW MRI has demonstrated the potential to improve the specificity of breast MRI, facilitate the evaluation of tumor response to neoadjuvant chemotherapy and can be employed in unenhanced MRI screening. However, standardization of the acquisition and interpretation of DW MRI is challenging. Recently, the European Society of Breast Radiology issued a consensus statement, which described the acquisition parameters and interpretation of DW MRI. The current article describes the basic principles, standardized acquisition protocols and interpretation guidelines, and the clinical applications of DW MRI in breast imaging.

Keywords: Cancer; Dense breast; Diffusion-weighted MRI; Standardization; Supplemental screening.

Fig. 1. Standard DW image sets.

DW image sets consist of T2-weighted reference image obtained without diffusion gradients (A), DW images obtained with diffusion gradients (b value of 800 sec/mm²) (B), and the parametric ADC map (C). An area of restricted diffusion with breast cancer (arrow) appears bright on the DW image and dark on the ADC map. ADC = apparent diffusion coefficient, DW = diffusion-weighted, S₀ = signal intensity with b = 0 s/mm², S_D = signal intensity with b = 800 s/mm²

Fig. 2. Effect of b value on the signal intensity of normal breast parenchyma and benign and malignant breast lesions.

As the b value increases (A–G), the signal intensity of normal breast parenchyma (background diffusion signal) and a biopsy-proven fibroadenoma (arrowhead) decreases, whereas the signal intensity of an invasive ductal carcinoma (arrow) remains high, increasing the lesion visibility and specificity for lesion detection, despite the lower signal-to-noise ratio. On the ADC map calculated using the b values of 0 sec/mm² and 800 sec/mm² (H), the breast cancer appears as dark signal intensity (ADC value, 0.90 × 10⁻³ mm²/sec), while the fibroadenoma appears as high signal intensity (ADC value, 1.71 × 10⁻³ mm²/sec).

Fig. 3. DW MRI acquired using different acquisition techniques at the b value of 1000 sec/mm².

A. Single-shot EPI with in-plane resolution of 1.3 × 1.3 mm². B. Readout-segmented EPI with in-plane resolution of 1.3 × 1.3 mm². C. Reduced field of view technique with in-plane resolution of 0.59 × 0.59 mm². The T1-weighed dynamic contrast-enhanced MRI with in-plane resolution of 0.9 × 0.9 mm². D. Demonstrates two adjacent irregular enhancing masses. Core needle biopsy and conservation surgery revealed two adjacent grade 2 invasive ductal carcinomas of size 2.4 cm and 0.5 cm. EPI = echo-planar imaging, MRI = magnetic resonance imaging

Fig. 4. The degree of background diffusion signals on DW MRI.

MIP images of DW MRI acquired at the b value of 1200 sec/mm² displaying minimal (A), mild (B), moderate (C), and marked (D) background diffusion signals. MIP = maximum intensity projection

Fig. 5. Lesion detection and characterization on DW MRI.

Sagittal image from dynamic contrast-enhanced MRI (A) shows an irregular enhancing mass (arrow) in the left breast at the 1 o'clock position. On reconstructed sagittal MIP of DW MRI obtained with a b value of 1200 sec/mm² (B), a mass of high signal intensity (arrow) distinct from the background diffusion signal is easily detectable. On the corresponding axial images of DW MRI obtained with a b value of 800 sec/mm² (C) and ADC map (D), an irregular mass of high signal intensity (arrow) with a low mean ADC of 0.97 × 10⁻³ mm²/sec is demonstrated. Core needle biopsy and conservation surgery revealed a grade 2 invasive ductal carcinoma of size 1.5 cm.

Fig. 6. Interpretation guideline used in a prospective multicenter study (clinicaltrials.gov Identifier: NCT03835897) for 3T screening DW MRI with b values of 0, 800, and 1200 sec/mm².

^*ADC map is calculated from b = 0 and 800 sec/mm² DW image, ^†Focus is evaluated based on both SI on b = 0 sec/mm² and ADC value (× 10⁻³ mm²/sec). FU = follow-up, SI = signal intensity