Diffusion-Weighted MRI of Breast Cancer: Improved Lesion Visibility and Image Quality Using Synthetic b-Values

Background: Diffusion-weighted imaging (DWI) is an MRI technique with the potential to serve as an unenhanced breast cancer detection tool. Synthetic b-values produce images with high diffusion weighting to suppress residual background signal, while avoiding additional measurement times and reducing artifacts. Purpose: To compare acquired DWI images (at b = 850 s/mm(2)) and different synthetic b-values (at b = 1000-2000 s/mm(2)) in terms of lesion visibility, image quality, and tumor-to-tissue contrast in patients with malignant breast tumors. Study Type: Retrospective. Population: Fifty-three females with malignant breast lesions. Field Strength/Sequence: T(2)w, DWI EPI with STIR fat-suppression, and dynamic contrast-enhanced T(1)w at 3T. Assessment: From acquired images using b-values of 50 and 850 s/mm(2), synthetic images were calculated at b = 1000, 1200, 1400, 1600, 1800, and 2000 s/mm(2). Four readers independently rated image quality, lesion visibility, preferred b-value, as well as the lowest and highest b-value, over the range of b-values tested, to provide a diagnostic image. Statistical Tests: Medians and mean ranks were calculated and compared using the Friedman test and Wilcoxon signed-rank test. Reproducibility was analyzed by intraclass correlation (ICC), Fleiss, and Cohen's kappa. Results: Relative signal-to-noise and contrast-to-noise ratios decreased with increasing b-values, while the signal-intensity ratio between tumor and tissue increased significantly (P < 0.001). Intermediate b-values (1200-1800 s/mm(2)) were rated best concerning image quality and lesion visibility; the preferred b-value mostly lay at 1200-1600 s/mm(2). Lowest and highest acceptable b-values were 850 s/mm(2) and 2000 s/mm(2). Interreader agreement was moderate to high concerning image quality (ICC: 0.50-0.67) and lesion visibility (0.70-0.93), but poor concerning preferred and acceptable b-values (kappa = 0.032-0.446). Data Conclusion: Synthetically increased b-values may be a way to improve tumor-to-tissue contrast, lesion visibility, and image quality of breast DWI, while avoiding the disadvantages of performing DWI at very high b-values. Level of Evidence: 3 Technical Efficacy: Stage 2