Patent ID: 6011392
Filing Date: 2000-01-04
Classification: G01R

Abstract:
An NMR system, the combination comprising:means for generating a polarizing magnetic field;excitation means for generating an RF magnetic field which produces transverse magnetization in spins subjected to the polarizing magnetic field;receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized samples of the NMR signal;first gradient means for generating a first magnetic field gradient to phase encode the NMR signal;second gradient means for generating a second magnetic field gradient to frequency encode the NMR signal;third gradient means for generating a third magnetic field gradient to select a region from which NMR signals are acquired; andpulse control means coupled to the excitation means, first gradient means, second gradient means, third gradient means and receiver means, said pulse control means being operable to conduct a scan in which a pulse sequence is conducted to acquire digitized samples of NMR signals which enable an image to be constructed, wherein the pulse control means operates during the scan to perform a fast spin echo pulse sequence in which a series of RF refocusing pulses are produced by said excitation means to produce a corresponding series of NMR spin echo signals, a pair of crusher gradient pulses are produced by the third gradient means surrounding each RF refocusing pulse, and a compensating gradient is produced by said third gradient means during an interval adjacent to the first RF refocusing pulse in said series of RF refocusing pulses to reduce image artifacts produced by Maxwell terms, the compensating gradient is produced by changing the shape of a crusher gradient pulse associated with the first RF refocusing pulse and the crusher gradient pulses associated with RF refocusing pulses after said first RF refocusing pulse are shaped the same as the changed crusher gradient pulse associated with the first RF refocusing pulse.