MRI method of phase shift measurement, MRI method of phase shift correction, and MRI apparatus carrying out these methods

摘要

For the accurate measurement of the phase shift of echos caused by the inference of the eddy current and residual magnetization attributable to the encode gradient and the like, the measuring process includes the steps of emitting an excitation pulse R, emitting an inversion pulse Pl, applying an encode gradient gyn to the phase axis, applying a read gradient gxr, which is the former half of the usual read gradient, to the read axis, applying a rewind gradient gyrn in which a compensation pulse gypn is put to the phase axis, emitting an inversion pulse P2, applying a dephaser gradient gywdn to the phase axis, sampling data from the echo2 while applying a readout gradient gywn to the phase axis, evaluating the phase shift value of the echo2 caused by the influence of the encode gradient gyn and rewind gradient gyrn based on phase data resulting from the first-order Fourier transform for the sampled data, determining the correction value from the resulting phase shift value, revising the compensation pulse gypn with the correction value, and repeatting these operations an intended number of times while altering the encode gradient gyn.