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Quantitative Diffusion-Weighted Imaging as an Adjunct to Conventional Breast MRI for Improved Positive Predictive Value

¹ Department of Radiology, University of Washington, Seattle Cancer Care Alliance, 825 Eastlake Ave. E, G3-200, Seattle, WA 98109-1023.
² Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA.

OBJECTIVE. The purpose of our study was to investigate whether adding diffusion-weighted imaging (DWI) to dynamic contrast-enhanced MRI (DCE-MRI) could improve the positive predictive value (PPV) of breast MRI.

MATERIALS AND METHODS. The retrospective study included 70 women with 83 suspicious breast lesions on DCE-MRI (BI-RADS 4 or 5) who underwent subsequent biopsy. DWI was acquired during clinical breast MRI using b = 0 and 600 s/mm². Apparent diffusion coefficient (ADC) values were compared for benign and malignant lesions. PPV was calculated for DCE-MRI alone (based on biopsy recommendations) and DCE-MRI plus DWI (adding an ADC threshold) for the same set of lesions. Results were further compared by lesion type (mass, nonmasslike enhancement) and size.

RESULTS. Of the 83 suspicious lesions, 52 were benign and 31 were malignant (11 ductal carcinoma in situ [DCIS], 20 invasive carcinoma). Both DCIS (mean ADC, 1.31 ± 0.24 x 10^–3 mm²/s) and invasive carcinoma (mean ADC, 1.29 ± 0.29 x 10^–3 mm²/s) exhibited lower mean ADC than benign lesions (1.70 ± 0.44 x 10^–3 mm²/s, p < 0.001). Applying an ADC threshold of 1.81 x 10^–3 mm²/s for 100% sensitivity produced a PPV of 47% versus 37% for DCE-MRI alone, which would have avoided biopsy for 33% (17/52) of benign lesions without missing any cancers. DWI increased PPV similarly for masses and nonmasslike enhancement and preferentially improved PPV for smaller ( 1 cm) versus larger lesions.

CONCLUSION. DWI shows potential for improving the PPV of breast MRI for lesions of varied types and sizes. However, considerable overlap in ADC of benign and malignant lesions necessitates validation of these findings in larger studies.

Keywords: apparent diffusion coefficient (ADC) • breast • diffusion-weighted MRI • MRI • positive predictive value

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