Restriction spectrum imaging (RSI) decomposes the diffusion-weighted MRI signal into separate components of known apparent diffusion coefficients (ADCs). The number of diffusion components and optimal ADCs for RSI are organ-specific and determined empirically. The purpose of this work was to determine the RSI model for breast tissues. Methods:The diffusion-weighted MRI signal was described using a linear combination of multiple exponential components. A set of ADC values was estimated to fit voxels in cancer and control ROIs. Later, the signal contributions of each diffusion component were estimated using these fixed ADC values. Relative-fitting residuals and Bayesian information criterion were assessed. Contrast-to-noise ratio between cancer and fibroglandular tissue in RSI-derived signal contribution maps was compared to DCE imaging.Results: A total of 74 women with breast cancer were scanned at 3.0 Tesla MRI.The fitting residuals of conventional ADC and Bayesian information criterion suggest that a 3-component model improves the characterization of the diffusion signal over a biexponential model. Estimated ADCs of triexponential model were

The role of diffusion weighted imaging (DWI) as a biomarker has been the subject of active investigation in the field of breast radiology. By quantifying the random motion of water within a voxel of tissue, DWI provides indirect metrics that reveal cellularity and architectural features. Studies show that data obtained from DWI may provide information related to the characterization, prognosis, and treatment response of breast cancer. The incorporation of DWI in breast imaging demonstrates its potential to serve as a non-invasive tool to help guide diagnosis and treatment. In this review, current technical literature of diffusion-weighted breast imaging will be discussed, in addition to clinical applications, advanced techniques, and emerging use in the field of radiomics.

Background To date, the accuracy and variability of diffusion‐weighted MRI (DW‐MRI) metrics have been reported in a limited number of scanner/protocol/coil combinations. Purpose To evaluate the reproducibility of DW‐MRI estimates across multiple scanners and DW‐MRI protocols and to assess the effects of using an 8‐channel vs. 16‐channel breast coil in a breast phantom. Study Type Prospective. Phantom Breast phantom containing tubes of water and differing polyvinylpyrrolidone (PVP) concentrations with apparent diffusion coefficients (ADCs) matching breast tissue. Field Strength/Sequence 3 T (three standard and one wide bore), three DW‐MRI single‐shot echo planar imaging protocols of varying acquired spatial resolution. Assessment Accuracy of estimated ADCs was assessed using percent differences (PD) relative to nuclear magnetic resonance spectroscopy‐derived reference values. Coefficients of variation (CV) were calculated to determine variation across scanners. CVs based on the median standard deviation (CVM) were used to evaluate tube‐specific dispersion using 8‐ or 16‐channel coils at a single scanner. ADCs of PVP‐containing tubes were additionally normalized by the median water tube ADC to account for temperature effects. Statistical Tests Two‐way repeated measures analysis of variance and post hoc tests were used to evaluate differences in ADC, CV, and CVM across scanners and protocols (α = 0.05). Results ADCs were within 11% (interquartile range [IQR] 7%) of reference values and significantly improved to 2% (IQR 7%) after normalization to an internal water reference. Normalization significantly reduced interscanner variability of ADC estimates from 7% to 4%. DW‐MRI protocol did not affect ADC accuracy; however, the clinical and higher‐resolution clinical protocols resulted in the greatest (9%) and least (6%) interscanner variability, respectively. The 8‐ and 16‐channel receive coils yielded similar accuracy (PD: 12% vs. 16%) and precision (CVM: 2.7% vs. 2.9%). Data Conclusion Normalization by an internal reference improved interscanner ADC reproducibility. High‐resolution protocols yielded comparably accurate and significantly less variable ADCs compared to a clinical standard protocol. Evidence Level 2 Technical Efficacy Stage 1

Background Diffusion‐weighted (DW) echo‐planar imaging (EPI) is prone to geometric distortions due to B0 inhomogeneities. Both prospective and retrospective approaches have been developed to decrease and correct such distortions. Purpose The purpose of this work was to evaluate the performance of reduced‐field‐of‐view (FOV) acquisition and retrospective distortion correction methods in decreasing distortion artifacts for breast imaging. Coverage of the axilla in reduced‐FOV DW magnetic resonance imaging (MRI) and residual distortion were also assessed. Study Type Retrospective. Population/Phantom Breast phantom and 169 women (52.4 ± 13.4 years old) undergoing clinical breast MRI. Field Strength/Sequence A 3.0 T/ full‐ and reduced‐FOV DW gradient‐echo EPI sequence. Assessment Performance of reversed polarity gradient (RPG) and FSL topup in correcting breast full‐ and reduced‐FOV EPI data was evaluated using the mutual information (MI) metric between EPI and anatomical images. Two independent breast radiologists determined if coverage on both EPI data sets was adequate to evaluate axillary nodes and identified residual nipple distortion artifacts. Statistical Tests Two‐way repeated‐measures analyses of variance and post hoc tests were used to identify differences between EPI modality and distortion correction method. Generalized linear mixed effects models were used to evaluate differences in axillary coverage and residual nipple distortion. Results In a breast phantom, residual distortions were 0.16 ± 0.07 cm and 0.22 ± 0.13 cm in reduced‐ and full‐FOV EPI with both methods, respectively. In patients, MI significantly increased after distortion correction of full‐FOV (11 ± 5% and 18 ± 9%, RPG and topup) and reduced‐FOV (8 ± 4% both) EPI data. Axillary nodes were observed in 99% and 69% of the cases in full‐ and reduced‐FOV EPI images. Residual distortion was observed in 93% and 0% of the cases in full‐ and reduced‐FOV images. Data Conclusion Minimal distortion was achieved with RPG applied to reduced‐FOV EPI data. RPG improved distortions for full‐FOV images but with more modest improvements and limited correction near the nipple. Evidence Level 3 Technical Efficacy Stage 1

Diffusion-weighted MRI (DW-MRI) offers a potential adjunct to dynamic contrast-enhanced MRI to discriminate benign from malignant breast lesions by yielding quantitative information about tissue microstructure. Multi-component modeling of the DW-MRI signal over an extended b-value range (up to 3000 s/mm2) theoretically isolates the slowly diffusing (restricted) water component in tissues. Previously, a three-component restriction spectrum imaging (RSI) model demonstrated the ability to distinguish malignant lesions from healthy breast tissue. We further evaluated the utility of this three-component model to differentiate malignant from benign lesions and healthy tissue in 12 patients with known malignancy and synchronous pathology-proven benign lesions. The signal contributions from three distinct diffusion compartments were measured to generate parametric maps corresponding to diffusivity on a voxel-wise basis. The three-component model discriminated malignant from benign and healthy tissue, particularly using the restricted diffusion C1 compartment and product of the restricted and intermediate diffusion compartments (C1 and C2). However, benign lesions and healthy tissue did not significantly differ in diffusion characteristics. Quantitative discrimination of these three tissue types (malignant, benign, and healthy) in non-pre-defined lesions may enhance the clinical utility of DW-MRI in reducing excessive biopsies and aiding in surveillance and surgical evaluation without repeated exposure to gadolinium contrast.