Intracellular water lifetime measured by diffusion weighted and dynamic contrast enhanced MRI

Introduction: Intracellular water lifetime (τi) is closely related to membrane permeability and intracellular water diffusivity in addition to size and shape of the cells [1, 2]. The importance of this parameter is paramount in understanding MR data, particularly for diffusion and perfusion experiments. Dynamic contrast enhanced (DCE)-MRI of a diffusible tracer has been widely used for diagnosis of cancer and monitoring treatment response. However, extracting physiologically relevant parameters from DCE-MRI data is still a challenging problem. Gd-DTPA particles do not enter the intracellular space. In MRI, the contrast agent concentration is indirectly measured by its effect on water molecules which can access all tissue compartments. It has been reported earlier that water exchange between interstitium and intracellular space may not be fast enough to be ignored in DCE-MRI [3]. Cross-validation of such effect in DCE-MRI is not trivial. Exchange of intracellular water affects diffusion measurement. It has also been reported that τi can be measured by constant gradient diffusion weighted imaging (DWI) experiment [4]. Thus, the objective of this study was to compare intracellular water lifetimes measured by in vivo DCE-MRI and DWI experiment in a mouse tumor model.