Intravoxel Incoherent Motion Diffusion-Weighted MRI at 3.0 T Differentiates Malignant Breast Lesions From Benign Lesions and Breast Parenchyma

DIFFUSION-WEIGHTED (DW) magnetic resonance imaging (MRI) and measurements of the apparent diffusion coefficient (ADC) have proven useful in the detection and characterization of cancer (1). The ADC is sensitive to tissue cellularity and is usually lower in malignant tumors, in which water diffusion is more restricted because of the increased cell density and reduced extracellular space compared to the normal tissue. DW images may also reflect perfusion effects, as the microscopic blood flow in a randomly oriented capillary network creates a pseudodiffusion contribution to the DW signal. This effect, known as the intravoxel incoherent motion (IVIM) (2), has been observed in a variety of well-vascularized tissues, including brain, liver, pancreas, kidney, muscle, and placenta (3–8). The IVIM measurements have been reported in liver lesions (9), prostate cancer (10), and head and neck cancer (11,12) and used to differentiate pancreatic tumors (5) and salivary gland tumors (12). The IVIM component may reduce the accuracy of cancer differentiation using ADC by introducing a positive bias proportional to the perfusion fraction (13) into the ADC values and increasing their variability and dependence on the choice of the diffusion-weighting factors, or b-values (14,15). The b-value scheme also strongly affects the IVIM parameters and the separation between their values in cancer and normal tissue when the number of b-values is small (10). Therefore, the reliability of the IVIM measurements achievable in clinical practice and their usefulness in cancer diagnosis need to be further evaluated. In the diagnosis of breast lesions, DW imaging may be used as an adjunct technique to the contrast-enhanced MRI, which provides high sensitivity, but limited specificity (16). Differentiation between malignant and benign breast lesions based on ADC has been shown to achieve a sensitivity of 85–95% and a specificity of 50–90% (15,17–21). Perfusion effects are negligible in the DW signal of normal breast parenchyma, as shown by Baron et al (22) in healthy volunteers, but can be appreciable in breast cancer (15,23). In patients with locally advanced breast cancer, Sigmund et al (24) found the average perfusion fraction in tumors to be about 10% (range, 3–22%) and demonstrated that the true diffusion coefficient provided a better separation between cancer and fibroglandular tissue (FGT) than the ADC. In agreement with Baron et al (22), Sigmund et al (24) found that the IVIM contribution in normal parenchyma was small; however, neither study reported the perfusion fraction values in FGT. Such estimates may be useful as a measure of robustness of the IVIM measurements. The purpose of this study was to use DW MRI at 3.0 T and 1) measure the IVIM parameters in breast parenchyma in high-risk normal subjects and determine a range of b-values that provide reliable IVIM parameter estimates; 2) determine the IVIM parameters in malignant and benign breast lesions and normal parenchyma in patients with breast lesions; and 3) assess the ability of the IVIM parameters and ADC to differentiate malignant lesions from benign lesions and FGT.