This proposal is centered around Magnetic Resonance Imaging (MRI) Guided Focused Ultrasound (FUS) and two of its medical applications, tumor ablation and gene therapy. FUS has been known to be very effective to heat tissue locally. However, problems with the localization and dosimetry of | thermal dose have prevented widespread use. MRI temperature imaging combined with anatomical MRI can help to overcome | these problems. The research will be centered around the development of ultrafast noninvasive temperature imaging in vivo and the design effective FUS within the MR magnet. | Two possible applications will be further investigated: | I) Application of high intensity FUS to destroy a tumor without damaging surrounding tissue. 2) Temporal and spatial control of expression of a therapeutic gene, sensitized to heat using the Heat Shock Protein prom | Thus, high local and temporal control of gene therapy can be achieved using controlled periods of local heat elevation.