A method may include obtaining first image data of a first subject and obtaining a target machine learning model. The first image data may indicate a first intensity distribution of a first magnetic field relative to at least one portion of the first subject. The target machine learning model may provide a mapping relationship between second intensity distributions of second magnetic fields and corresponding second susceptibility distributions associated with second subjects under the second magnetic fields. The method may also include generating a first susceptibility distribution associated with the first subject under the first magnetic field based on the target machine learning model and the first image data. The method may further include determining a target MR image of the at least one portion of the first subject based on the first susceptibility distribution.
