Automatic, localized in vivo adjustment of all first- and second-order shim coils.
The implementation of a "fast, automatic shimming technique by mapping along projections" (FASTMAP) on a 2.1-Tesla whole-body system is described. The method provides a localized adjustment of all first- (X, Y, Z) and second-order (Z2, ZX, ZY, X2-Y2, 2XY) coils in 2 min. The time savings are achieved by mapping the magnetic field along six projections rather than from whole-imaging data sets. An analysis of noise error propagation suggests that in 64-ml volumes the residual linewidths obtained with the method are negligible when the signal-to-rms-noise ratio is above 30. The initial application of the method to localized 13C, 31P, and 1H spectroscopy of the human brain resulted in linewidths of approximately 2 Hz for 13C (144-ml volume), approximately 2.5 Hz for 31P (36-ml volume) and approximately 4 Hz for 1H (36-ml volume) with symmetric and reproducible lineshapes.
Gruetter
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Department of Molecular Biology and Biochemistry, Yale University, New Haven, Connecticut.
D001921:Brain / Q000033:anatomy & histology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors