Purpose-The objective of this study was to assess changes in the water apparent diffusion coefficient (ADC) and in pharmacokinetic parameters obtained from the fast-exchange regime (FXR) modeling of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) during neoadjuvant chemotherapy in breast cancer.Materials and Methods-Eleven patients with locally advanced breast cancer underwent MRI examination prior to and after chemotherapy but prior to surgery. A 1.5-T scanner was used to obtain T 1 , ADC and DCE-MRI data. DCE-MRI data were analyzed by the FXR model returning estimates of K trans (volume transfer constant), ν e (extravascular extracellular volume fraction) and τs i (average intracellular water lifetime). Histogram and correlation analyses assessed parameter changes posttreatment.Results-Significant ( P <.05) changes or trends towards significance ( P <.10) were seen in all parameters except τ i , although there was qualitative reduction in τ i values post-treatment. In particular, there was reduction ( P <.035) in voxels with K trans values in the range 0.2-0.5 min -1 and a decrease ( P <.05) in voxels with ADC values in the range 0.99×10 -3 to 1.35×10 -3 mm 2 /s. ADC and ν e were negatively correlated (r = -.60, P <.02). Parameters sensitive to water distribution and geometry (T 1 , ν e ,τs i and ADC) correlated with a multivariable linear regression model. Conclusion-The analysis presented here is sensitive to longitudinal changes in breast tumor status; K trans and ADC are most sensitive to these changes. Relationships between parameters provide information on water distribution and geometry in the tumor environment.

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