Radio frequency impedance mapping (RFIM) is a proposed new medical imaging modality. Image intensity in RFIM is based on the local electrical properties (namely conductivity and permittivity) of tissues inside the body. Since these properties vary widely between different tissues and notably, between normal and malignant tissues, images based on these properties should have significant diagnostic value. Potential clinical applications include cancer detection and imaging of conditions such as myocardial ischemia, cerebral edema, and spreading depression. In RFIM imaging, a large array of radio frequency coils (such as are used in magnetic resonance imaging) are placed on the patient. Measurements of the impedance matrix (or S parameters) of the array are used to derive a system of equations that constrain the local electrical properties of the patient's body. These equations are then solved to obtain an image. The patient is not exposed to ionizing radiation or high levels of radio frequency power. Preliminary work on RFIM has included both numerical simulations and experimental work. The simulations indicate that RFIM is capable of producing accurate, fully three-dimensional images of internal anatomy. Early experimental results have begun to confirm this. The proposed project will involve staged development of a prototype RFIM imaging system. The prototype will be tested to determine the overall feasibility of RFIM, including tests of the achievable resolution, reconstruction accuracy, and sensitivity to tumor-like variations in conductivity and permittivity. Results from the study will enable early assessment of the feasibility of RFIM, and the prototype will serve as a starting point for future designs. Successful implementation of RFIM will provide a new and potentially robust technique for measurement of tissue dielectric properties. Furthermore, RFIM is highly non-invasive and RFIM imaging systems are likely to be both inexpensive and easily portable.
