Method for correcting position deviation due to static magnetic field change in NMR imaging device

Claim 1

In an NMR imaging device comprising means for applying a static magnetic field to an object to be examined, means for applying to the object a gradient magnetic field in a slice direction, a gradient magnetic field in a phase encode direction and a magnetic field in a frequency encode direction, means for applying radio frequency pulses to the object to cause nuclear magnetic resonance (NMR) in atomic nuclei of atoms constituting tissues of the object, means for detecting the NMR signals thus generated, and means for Fourier-transforming the NMR signals to reconstruct an NMR image, a method for correcting deviation of a static magnetic field intensity comprising the steps of: a first step of placing the object in the static magnetic field; a second step of applying the gradient magnetic field in the slice direction and also applying a 90 degree radio frequency pulse at a preset center frequency of ω 0 corresponding to a slice position, which is decided by said static magnetic field and said gradient magnetic field in the slice direction; a third step of, after the application of said gradient magnetic field in the slice direction and said 90 degree radio frequency pulse have been cancelled during a predetermined period, applying the gradient magnetic field in the slice direction and a 180 degree radio frequency pulse at a center frequency of ω 0 ; a fourth step of detecting an NMR signal thus produced; a fifth step of Fourier-transforming said NMR signal to provide a peak frequency ω 1 of the resultant frequency spectrum; and a sixth step of obtaining the frequency difference between ω 0 and ω 1 and adding it to the frequency ω 0 .