Diffusion MRI results for assessing therapeutic efficacy of yCD (lower right panel of images) and yCD-UPRT (upper right panel of images) gene therapies of intracranial 9L gliosarcomas. The ADC maps on the right and the percentage change in mean ADC on the left show that the more stable yCD-UPRT enzyme is significantly faster and more effective in killing the 9L tumors than the yCD enzyme.