A spiral volume coil for improved RF field homogeneity at high static magnetic field strength

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Abstract
Biological samples have a high dielectric constant that can shorten RF wavelengths by a factor of 8 relative to the vacuum. At high field strengths, finite wavelength effects within larger samples are the dominant cause of RF field nonunifor‐mity. A coil design is presented that can reduce and even eliminate this inhomogeneity; 4‐T images in phantoms and in the head of a normal volunteer are presented, which demonstrate improved homogeneity relative to a standard coil. This coil design should aid in realizing the potential advantages of imaging large samples at high field strengths.