Multidimensional diffusion MRI for monitoring radiotherapy response in human prostate cancer xenografts in mice: A longitudinal pilot study

We use multidimensional diffusion MRI to monitor longitudinal effect of external radiotherapy in human prostate cancers in mice. The measured dimensions are “diffusion time” and “shape of the b-tensor,” enabling a probe of tissue heterogeneity, microscopic anisotropy and restriction sizes. We show that the diffusivity is highly time dependent in all tumors, and that it is significantly altered by radiotherapy, already within 1-15 days of treatment. The largest effect is seen for the diffusivity and its time dependence, but the isotropic diffusional variance is also impacted. Throughout, histology is used qualitatively to provide plausible interpretations to the observations.