Magnetic resonance imaging (MRI) is a diagnostic study that makes pictures of organs of the body using magnetic field and radio frequency pulses that can not be felt. The purpose of this study is to determine if a new MR imaging method can help tumor evaluation in head and neck cancer or prostate cancer. The extra images will be obtained using Diffusion-weighted Magnetic Resonance Imaging which provides image contrast through detection of small restrictions in the movement of water molecules. This study may help us provide additional information about the tumor along with the picture of the organ.