Tissue conductivity and permittivity are critical to understanding local radio frequency (RF) power deposition during magnetic resonance imaging (MRI). These electrical properties are also important in treatment planning of RF thermotherapy methods (e.g. RF hyperthermia). The electrical properties may also have diagnostic value as malignant tissues have been reported to have higher conductivity and higher relative permittivity than surrounding healthy tissue. In this study, we consider imaging conductivity and permittivity using MRI transmit field maps (B1+ maps) at 3.0 Tesla. We formulate efficient methods to calculate conductivity and relative permittivity from 2-dimensional B1+ data and validate the methods with simulated B1+ maps, generated at 128 MHz. Next we use the recently introduced Bloch-Siegert shift B1+ mapping method to acquire B1+ maps at 3.0 Tesla and demonstrate conductivity and relative permittivity images that successfully identify contrast in electrical properties.
Keywords: Hyperthermia; Magnetic resonance imaging; Oncology; Tissue conductivity; Tissue permittivity.