Mapping of the B1 field distribution of a surface coil resonator using EPR imaging.

Surface coil resonators have been widely used to perform topical EPR spectroscopy. They are usually positioned adjacent to or implanted within the body. For EPR applications these resonators have a number of important advantages over other resonator designs due to their ease of sample accessibility, mechanical fabrication, implementation of electronic tuning and coupling functions, and low susceptibility to sample motions. However, a disadvantage is their B(1) field inhomogeneity, which limits their usefulness for 3D imaging applications. We show that this problem can be addressed by mapping and correcting the B(1) field distribution. We report the use of EPR imaging (EPRI) to map the B(1) distribution of a surface coil resonator. We show that EPRI provides a fast, accurate, and reliable technique to evaluate the B(1) distribution. 3D EPRI was performed on phantoms, prepared using three different saline concentrations, to obtain the B(1) distribution. The information obtained from the phantoms was used to correct the images of living animals. With the use of this B(1) correction technique, surface coil resonators can be applied to perform 3D mapping of the distribution of free radicals in biological samples and living systems.