MR-Guided RF Ablation ofthe Liver

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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. Consequently, repeatable ablation volumes are difficult to produce. Our goal is to enhance the planning, control and efficacy of tumor ablation by using an MRI system that can map RF ablation currents local to the electrodes 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 estimates RF current density in tissue. The ablation electrode can be injected with RF currents at the resonant frequency of the MRI scanner, and can also act as an MRI receiver. The MRI scanner can directly image the intense magnetic fields associated with the ablation current, and then derive the local electrode current flow to 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.