We propose to design and test systems for the ablation of pancreatic cancer and other retroperitoneal malignancies using magnetic resonance thermal imaging (MRTI) within a 3 Tesla magnetic resonance. We will design and test ultrasonic delivery systems using ultrasonic applicators directly inserted into tumors (interstitial applicators), as well as an existing ultrasonic array system external to the body. Additionally, we will develop MRI-based 3-dimensional techniques for patient specific treatment planning, and robust MRTI techniques for monitoring retroperitoneal tumor ablation. In vivo studies using an animal model will allow determination of MRTI accurately to portray tissue ablation in real time, and avoid damage to normal structures adjacent to tumors. The in vivo studies of acute and longer-term changes to tissues during ablation will also investigate several types of MR imaging, including T2-weighted, diffusion weighted, contrast- enhanced and MR images encoding tissue stiffness, following ablative procedures. Histologic/MRI correlations will allow for determination of the ability of such images accurately to portray tissue changes resulting from the ablative procedures. The clinical importance of the project stems from the fact that the major cancer targeted, pancreatic cancer is currently the fourth leading cause of cancer death in the United States; it is nearly uniformly fatal, since early local extension with encasement of blood vessels makes surgery impossible in about 90% of cases, and other treatment modalities are of limited effectiveness. The controlled thermal techniques proposed should be capable of ablating cancers extending to blood vessels, which cannot be treated surgically. The technologies and techniques, to be developed should allow effective treatment of pancreatic cancer and other retroperitoneal malignancies with minimal damage to normal structures and minimal side effects of treatment.