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.

Diffusion-weighted MRI shows promise in differentiation of benign and malignant masses and lesions with nonmasslike enhancement found at breast MRI and is not affected by lesion size. However, ADC measurements may be more useful for discriminating masses than for discriminating lesions with nonmasslike enhancement.

Purpose: To investigate the diagnostic performance of diffusion-weighted imaging (DWI) for mammographically and clinically occult breast lesions. Materials and Methods:The study included 91 women with 118 breast lesions (91 benign, 12 ductal carcinoma in situ [DCIS], 15 invasive carcinoma) initially detected on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and assigned BI-RADS category 3, 4, or 5. DWI was acquired with b ¼ 0 and 600 s/mm 2 . Lesion visibility was assessed on DWI. Apparent diffusion coefficient (ADC) values were compared between malignancies, benign lesions, and normal (no abnormal enhancement on DCE-MRI) breast tissue, and the diagnostic performance of DWI was assessed based on ADC thresholding.Results: Twenty-four of 27 (89%) malignant and 74/91 (81%) benign lesions were hyperintense on the b ¼ 600 s/ mm 2 diffusion-weighted images. Both DCIS (1.33 6 0.19 Â 10 À3 mm 2 /s) and invasive carcinomas (1.30 6 0.27 Â 10 À3 mm 2 /s) were lower in ADC than benign lesions (1.71 6 0.43 Â 10 À3 mm 2 /s; P < 0.001), and each lesion type was lower in ADC than normal tissue (1.90 6 0.38 Â 10 À3 mm 2 /s, P 0.001). Receiver operating curve (ROC) analysis showed an area under the curve (AUC) of 0.77, and sensitivity ¼ 96%, specificity ¼ 55%, positive predictive value (PPV) ¼ 39%, and negative predictive value (NPV) ¼ 98% for an ADC threshold of 1.60 Â 10 À3 mm 2 /s. MAGNETIC RESONANCE IMAGING (MRI) is playing a growing role in breast cancer detection, particularly for screening patients at high risk for cancer (1) and evaluating the extent of disease in patients with a recent diagnosis of cancer (2). Breast MRI currently relies on the differential enhancement between normal and malignant tissue on T1-weighted dynamic contrast-enhanced MRI (DCE-MRI) sequences. However, the requirement for intravenous administration of a gadolinium-based contrast agent increases the associated time, costs, and potential toxicity of the breast DCE-MRI examination. These factors limit the accessibility of this screening tool for many women. ConclusionDiffusion-weighted imaging (DWI) is a noncontrast MRI technique that has potential as an alternative breast imaging method without the risks and costs associated with DCE-MRI. DWI measures the mobility of water molecules in vivo and reflects characteristics of the microscopic cellular environment, including cell density, cell organization, and membrane integrity (3). DWI is an established diagnostic tool in neuroimaging, but application to other areas of the body has been challenging due to technical limitations. More recent advances in MR technology have facilitated the application of DWI for detecting and characterizing a variety of carcinomas outside of the brain (4-8). Preliminary DWI studies of the breast reported high sensitivity for detecting cancer, based on low diffusivity in carcinomas due to higher cell density (9-11). Furthermore, quantitative DWI analyses have shown that the apparent diffusion coefficient (ADC) is significantly lower in many breast carcinom...