The void under the knee of a supine patient leads to localized B0 magnetic field distortions due to air-tissue susceptibility differences. To cancel this local artifact, low-order harmonic shims are inadequate, but a single local shim coil can produce higher harmonic suppression. A half-cylinder version wrapped on the outside of the RF coil has been constructed and used to obtain in vivo data consistent with the magnetic field simulations. The detailed results support the possibility of an effective knee shimming approach.
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