Magnetic resonance imaging apparatus
AssigneeKabushiki Kaisha Toshiba
InventorYoshio Machida
Life of this patent
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Abstract
In a magnetic resonance imaging apparatus adapted for a spin-echo method using a 90.degree. pulse as a selective excitation pulse and a 180.degree. pulse as a refocus pulse, MR signal is acquired with their phase difference changed in increments of a fixed angle with each frequency encoding step. This permits the phase difference between an echo signal used for imaging and an FID signal unnecessary for imaging to be changed in increments of the fixed angle with each encoding step. Thus, a zipper artifact based on the FID signal will be produced in a position corresponding to the fixed angle in an MR image reconstructed through Fourier transform of the acquired signal. The proper setting of the fixed angle of the phase difference permits the zipper artifact to be shifted to any position in the MR image.
Claims12
A magnetic resonance imaging apparatus adapted for a spin-echo method using a selective excitation pulse and a refocus pulse as radio-frequency pulses comprising:
- sequence control means for carrying out a spin-echo pulse sequence while changing the phases of the RF pulses with each encoding step so that the phase difference between the selective excitation pulse and the refocus pulse is changed in increments of a fixed angle with each encoding step;
- and
- means for reconstructing an MR image on the basis of signals acquired in accordance with the spin-echo pulse sequence carried out by said sequence control means,
- whereby a phase difference between an echo signal induced by the selective excitation pulse and an FID (free induction decay) signal induced by the refocus pulse is changed in increments of said fixed angle with each encoding step, and an artifact based on the FID signal is produced in a position corresponding to said phase difference with respect to an image based on the echo signal.
A magnetic resonance imaging method for acquiring magnetic resonance signals from an object under examination to obtain an MR image, comprising:
- acquiring a first signal necessary for imaging and a second signal unnecessary for imaging;
- changing the phase difference of said first and second signals in increments of a predetermined amount with each encoding step;
- and
- obtaining an image from the first signal and an image from the second signal;
- wherein the relative positional relationship between said images from said first and second signals is dependent on said predetermined amount of phase difference.
A magnetic resonance imaging method comprising the steps of:
- (a) applying a selective excitation pulse and a refocus pulse to acquire an echo signal, the phase difference between the selective excitation and refocus pulses being kept at a predetermined angle .phi.;
- (b) repeating step (a) a number of times corresponding to the number of frequency encoding steps with the phase difference between the selective excitation pulse and refocus pulse being changed in increments of the predetermined angle .phi. with each encoding step;
- and
- (c) reconstructing an MR image on the basis of magnetic resonance signals obtained in step (b).
Dependencies are inferred from the claim text.