Magnetic resonance imaging method and apparatus to correct distortions due to inhomogeneities of the basic magnetic field

A magnetic resonance apparatus to correct distortions due to inhomogeneities of a basic magnetic field in magnetic resonance image data, comprising:

• a magnetic resonance data acquisition unit comprising a basic field magnet that generates a basic magnetic field exhibiting inhomogeneities, a gradient coil system and a radio-frequency system;
• a control unit configured to operate said magnetic resonance data acquisition unit to excite nuclear spins, with said radio-frequency system, in an examination subject at least partially located in said basic magnetic field and to acquire a first measurement data set and at least one additional measurement data set representing magnetic resonance signals resulting from the excitation of said nuclear spins, each of said first and said at least one additional measurement data set comprising a plurality of measurement points, said measurement points in said first measurement data set being acquired by operating said gradient coil system to activate a first number of magnetic field gradients in said magnetic resonance data acquisition unit, and each measurement point in said at least one additional measurement data set being acquired by operating said gradient coil system to activate a second number of magnetic field gradients being in said magnetic resonance data acquisition unit, said second number being larger than said first number;
• a computer provided with said first measurement data set and said at least one additional measurement data set, said computer being configured to reconstruct a first set of magnitude and phase values for each measurement point in said first measurement data set and a second set of respective magnitude and phase values for each measurement point in said at least one additional measurement data set;
• said computer being configured to determine a phase difference between respective corresponding measurement points of said first and said at least one additional measurement data set from the reconstructed phase values thereof;
• said computer being configured to determine a spatial shift for each measurement point of said first measurement data set from the determined phase difference;
• said computer being configured to distribute the reconstructed magnitude values for the respective measurement points of said first measurement data sets to generate respective image points of a corrected image data set, dependent on the determined spatial shift;
• and
• said computer being configured to make said corrected image data set available at an output of said computer as a data file.

A non-transitory computer-readable data storage medium encoded with programming instructions, said data storage medium being loaded into a computerized control and processing system of a magnetic resonance apparatus comprising a magnetic resonance data acquisition unit, in which a basic magnetic field exhibiting inhomogeneities is generated, said programming instructions causing said computerized control and processing system to:

• operate a magnetic resonance data acquisition unit, in which a basic magnetic field exhibiting inhomogeneities is generated, to excite nuclear spins in an examination subject at least partially located in said basic magnetic field and to acquire a first measurement data set and at least one additional measurement data set representing magnetic resonance signals resulting from the excitation of said nuclear spins, each of said first and said at least one additional measurement data set comprising a plurality of measurement points, said measurement points in said first measurement data set being acquired by activating a first number of magnetic field gradients in said magnetic resonance data acquisition unit and each measurement point in said at least one additional measurement data set being acquired with a second number of magnetic field gradients being activated in said magnetic resonance data acquisition unit, said second number being larger than said first number;
• reconstruct a first set of magnitude and phase values for each measurement point in said first measurement data set and a second set of respective magnitude and phase values for each measurement point in said at least one additional measurement data set;
• determine a phase difference between respective corresponding measurement points of said first and said at least one additional measurement data set from the reconstructed phase values thereof;
• determine a spatial shift for each measurement point of said first measurement data set from the determined phase difference;
• distribute the reconstructed magnitude values for the respective measurement points of said first measurement data sets to generate respective image points of a corrected image data set, dependent on the determined spatial shift;
• and
• make said corrected image data set available as an output as a data file.