Effect of degenerate spherical harmonics and a method for automatic shimming of oblique slices.
Several spherical harmonics degenerate on an oblique plane. Two-dimensional field mapping of an oblique slice causes ambiguity in determination of the degenerate spherical harmonics terms. Therefore, automatic shimming of oblique slices may lead to erroneous adjustment of shims corresponding to the degenerate spherical harmonics. In this paper an automatic slice shimming technique derived from the FASTMAP method (Gruetter R. Magn. Reson. Med. 1993; 29, 804-811) is proposed. This new method unequivocally determines and corrects all of the first- and the second-order shims for slices of arbitrary orientation.
Shen
J
J
The Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY 10962, USA.
D003952:Diagnostic Imaging / Q000295:instrumentation / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D008433:Mathematics; D019047:Phantoms, Imaging