Systematic passive shimming of a permanent magnet for P-31 NMR spectroscopy of bone mineral

Passive shimming of a relatively low-cost, medium-size, permanent magnet employing neodymium-iron-boron magnet material by the appropriate addition of steel is described. The magnet is for a low-field (0.33 T, 5.688 MHz) /sup 31/P NMR spectrometer built for the measurement of bone mineral in the human wrist and heel. The fuzzy logic and expert system features of the computer program used to enhance the shimming are discussed. The shimming procedure is described, and results are discussed.>