Method of correcting for magnetic field inhomogeneity in magnetic resonance imaging

A method of reducing slice thickness error to correct for gradient magnetic field inhomogeneity, the method comprising the steps of:

• (a) simultaneously applying an RF pulse sequence and a slice selection gradient Gz pulse sequence;
• (b) applying a frequency encoding/readout gradient Gz pulse sequence;
• (c) detecting magnetic resonance signals during the readout gradient Gx;
• and
• (d) repeating the steps (a) through (c) with identical pulse sequences, except that the slice selection gradient Gz is applied in the opposite direction.

A method of correcting for local dephasive magnetic resonance image signal loss due to magnetic field inhomogeneity, the method comprising the steps of:

• (a) simultaneously applying an RF pulse sequence and a slice selection gradient G.sub.z pulse sequence, the slice selection gradient G.sub.z sequence including a positive offset gradient G.sub.z lobe to produce approximately 50% signal reduction in a uniform magnetic field region;
• (b) applying a frequency encoding/readout gradient G.sub.x pulse sequence;
• (c) detecting magnetic resonance signals during the readout gradient G.sub.x ;
• (d) processing the detected magnetic resonance signals to obtain a complex image;
• (e) repeating the steps (a) through (d), with identical pulse sequences, except that the slice selection gradient G.sub.z sequence includes a negative offset gradient G.sub.z lobe that has the same amplitude and duration as the positive offset gradient G.sub.z lobe but is applied in the opposite direction from the positive offset gradient G.sub.z lobe;
• and
• (f) combining the two images acquired by the two pulse sequences, respectively.

A method of correcting for geometric distortion due to magnetic field inhomogeneity in magnetic resonance imaging (MRI), the method comprising the steps of:

• (a) simultaneously applying an RF pulse sequence and a slice selection gradient Gz pulse sequence to selectively excite magnetizations, wherein the selectively excited magnetizations have a predetermined resonant frequency;
• (b) simultaneously applying a compensation gradient Gz pulse sequence and a readout gradient pulse sequence, the compensation gradient Gz pulse sequence being applied in the same direction and having the same amplitude as the slice selection gradient Gz pulse sequence so that the previously selectively excited magnetizations will continue to have the same predetermined resonant frequency;
• and
• (c) repeating the steps (a) and (b), with the identical pulse sequences, except that both the slice selection gradient Gz and the compensation gradient Gz are applied in the opposite direction.