Diffusion-weighted MRI and response to anti-cancer therapies

In oncology practice, longitudinal studies are routinely conducted to monitor the size and enhancement of tumors in cancer patients undergoing therapy. Imaging protocols typically use gadolinium-enhanced T ₁-weighted images or T₂-weighted images from which tumor size is inferred and tumor response estimated. The past few years have also seen the emergence of diffusion-weighted magnetic resonance imaging (DWMRI) as a potential alternative to monitor therapeutic response (Kauppinen, R.A., NMR Biomed. 2002, 15, 6). The attractiveness of DWMRI resides in its ability to detect local microstructural changes associated with treatment long before their effects are translated into effective size changes. Damage to cell membrane integrity, changes in viscosity, and/or relative size of intra- vs. extracellular compartments all translate into changes in the apparent diffusion coefficient of tumor water measured by DWMRI. This dependence makes DWMRI a particularly sensitive method to detect response to a wide variety of chemotherapeutic agents. This review will focus on the emerging role of DWMRI to monitor the response of tumors to anti-cancer chemotherapies.