Method, apparatus and recording medium for measuring and correcting phase error in spins in a phase axis direction

A phase error measuring apparatus comprising:

• first means for effecting a 90° excitation on object spins, for effecting a first 180° excitation after a first time period from said 90° excitation, for effecting a second 180° excitation after a second time period from said first 180° excitation, and for effecting a third 180° excitation after said second time period from said second 180° excitation;
• second means for applying a first gradient magnetic field consisting of a first pulse of a first polarity, followed immediately by a second pulse of a second polarity opposite to said first polarity, followed immediately by a third pulse of said first polarity and having a time integral value of zero in a phase axis direction during time period from said first 180° excitation to said second 180° excitation to generate a first spin echo signal with a first phase error determined by distance from a peak of said first echo signal and a point in time when the time integral of said first pulse and said second pulse are equal, and for applying a second gradient magnetic field consisting of a first pulse of a first polarity followed immediately by a second pulse of a second polarity which is opposite to said first polarity followed immediately by a third pulse of said first polarity and having a time integral value of zero in the phase axis direction during the time period from said second 180° excitation to said third 180° excitation to generate a second spin echo signal with a second phase error determined by a distance from a peak of said second spin echo and a point in time when the time integral of said first pulse and second pulse are equal;
• and
• third means for determining a phase error of the spins in the phase axis direction due to residual magnetization or eddy current or combination thereof during the time period from said 90° excitation to said first 180° excitation based on calculation using said first phase error and said second phase error of said first and second spin echo signals.

A recording medium wherein being recorded in a computer readable manner with a program for causing a computer to execute the functions of:

• effecting a 90° excitation on object spins;
• effecting a first 180° excitation after a first time period from said 90° excitation;
• effecting a second 180° excitation after a second time period from said first 180° excitation;
• effecting a third 180° excitation after said second time period from said second 180° excitation;
• applying a first gradient magnetic field consisting of a first pulse of a second polarity followed immediately by a second pulse of a second polarity opposite to said first polarity, followed immediately by a third pulse of said first polarity and having a time integral value of zero in a phase axis direction during the time period from said first 180° excitation to said second 180° excitation to generate a first spin echo signal with a first phase error determined by distance from a peak of said first spin echo and a point in time when the time integral of said first pulse and said second pulse are equal;
• applying a second gradient magnetic field consisting of a first pulse of first polarity followed immediately by a second pulse of first polarity which is opposite to said polarity followed immediately by a third pulse of said selected first polarity and having a time integral value of zero in the phase axis direction during the time period from said second 180° excitation to said third 180° excitation to generate a second spin echo signal with a second phase error determined by distance from a peak of said second spin echo and a point in time when the time integral of said first pulse and second pulse are equal and
• determining a phase error of the spins in the phase axis direction due to residue magnetization or eddy current or combination thereof during the time period from said 90° excitation to said first 180° excitation based on calculation using said first phase error and said second phase error of said first and second spin echo signals.

A magnetic resonance imaging apparatus acquiring a magnetic resonance signal from a object using a static magnetic field, gradient magnetic fields, and a high frequency magnetic field, and constructing an image based on said acquired magnetic resonance signal, said apparatus comprising:

• first means for effecting a 90° excitation on object spins, for effecting a first 180° excitation after a first time period from said 90° excitation, for effecting a second 180° excitation after a second time period from said first 180° excitation, and for effecting a third 180° excitation after said second time period from said second 180° excitation;
• second means for applying a first gradient magnetic field consisting of a first pulse of first polarity, followed immediately by a second pulse of a second polarity opposite to said first polarity, followed immediately by a third pulse of said first polarity and having a time integral value of zero in a phase axis direction during time period from said first 180° excitation to said second 180° excitation to generate a first spin echo signal with a first phase error determined by distance from a peak of said first echo signal and a point in time when the time integral of said first pulse and said second pulse are equal, and for applying a second gradient magnetic field consisting of a first pulse of a first polarity followed immediately by a second pulse of a second polarity which is opposite to said first polarity followed immediately by a third pulse of said first polarity and having a time integral value of zero in the phase axis direction during the time period from said second 180° excitation to said third 180° excitation to generate a second spin echo signal with a second phase error determined by a distance from a peak of said second spin echo and a point in time when the time integral of said first pulse and said second pulse are equal;
• and
• third means for determining a phase error of the spins in the phase axis direction due to residual magnetization or eddy current or combination thereof during the time period from said 90° excitation to said first 180° excitation based on calculation using said first phase error and said second phase error of said first and second spin echo signals.