Patent ID: 9453897
Filing Date: 2016-09-27
CPC Classification: A61B,G01R

Claim Text:
1. A magnetic resonance imaging apparatus comprising: a static magnetic field generation unit that generates a static magnetic field in imaging space; a gradient magnetic field generation unit that generates a gradient magnetic field so as to be superimposed on the static magnetic field; a correction magnetic field generation unit that generates a correction magnetic field or correcting an error magnetic field generated in the imaging space due to application of the gradient magnetic field; a structural unit that supports the static magnetic field generation unit, the gradient magnetic field generation unit, and the correction magnetic field generation unit mounted inside; a measurement control unit that measures an echo signal from an object disposed in the imaging space on the basis of a predetermined pulse sequence; and a correction magnetic field calculation unit that calculates the correction magnetic field for correcting the error magnetic field generated in the imaging space due to application of the gradient magnetic field, wherein calculations by the correction magnetic field calculation unit include calculating the error magnetic field including a vibrational error magnetic field based on vibration of the structural unit due to application of the gradient magnetic field, and calculating the correction magnetic field for correcting the calculated error magnetic field; an error magnetic field measurement section that causes the measurement control unit to perform measurement of an echo signal using a pulse sequence having a test gradient magnetic field; an error magnetic field image acquisition section that acquires error magnetic field image data indicating distribution of the error magnetic field at each sampling time using the echo signal; an error magnetic field calculation section that calculates a parameter value of a damped vibration function showing the error magnetic field using the error magnetic field image data; and a correction magnetic field calculation section that calculates the correction magnetic field on the basis of the calculated parameter value, wherein the error magnetic field calculation section decomposes the error magnetic field image data into a plurality of spherical harmonic terms, calculates a parameter value including an attenuation time constant of the damped vibration function showing the error magnetic field by applying a Lorentzian function or a Gaussian function to a waveform near a frequency peak in a spectrum distribution in a frequency domain, which is obtained by performing a Fourier transform of the error magnetic field image data in a time axis direction, for each spherical harmonic term, and the correction magnetic field calculation section calculates the correction magnetic field for each spherical harmonic term on the basis of the calculated parameter value of the damped vibration function showing the error magnetic field for each spherical harmonic term.