Quantative MR-Guided Thermal and Electromagnetic Mapping of RF Ablations

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DESCRIPTION (provided by applicant): Radiofrequency ablation (RFA) is emerging as an effective image-guided minimally invasive therapeutic alternative to surgical treatment of cancer tumors. RFA appears well suited to nonresectable tumors in liver. The ablation process is highly dependent on the electrical conductivity of these tissues yet there is no easy way to predict the current pathways or how focused the current will be on the tumor. For example, bone and fatty pockets can shield tumor from ablation currents. Our goal is to enhance the planning and efficacy of tumor ablation by using an MRI system that can map RF ablation current pathways during ablation and map thermal changes. RF current maps will show where power is being deposited, and MR thermometry will show where heat flowed during the ablation. Our approach exploits a new MRI technique that images RF current density in tissue. The ablation electrode is injected with RF currents at the resonant frequency of the MRI scanner. The MRI scanner can directly image the intense magnetic fields associated with the ablation current, and then derive the map of current flow in tissue. In our preliminary work, we have already visualized the current flow in an MR compatible ablation electrode. These tests demonstrated that fatty tissue effectively insulates and blocks the ablation current. Moreover, the current pathway itself lights up high conductivity tissue and creates a medically significant contrast. To fully exploit this capability, we will merge RF current mapping with MR thermometry and ablation devices to form a comprehensive interventional MRI system for RF ablation. Enhanced RF hardware, pulse sequences and reconstructions will be developed. Upon completion, we will perform ex-vivo tissue sample and in-vivo animal studies to demonstrate the clinical potential of this system. If we achieve these goals, MR guided ablation imaging and thermal monitoring should enable better treatment planning for the ablation, and provide improved time and spatial monitoring as tumor ablation progresses. MR guided RF ablation gives the patient an effective option for a minimally invasive treatment of cancer tumors and a more controllable therapy.