MR imaging method, phase error measuring method and MRI system

An MR imaging method using a high-speed spin echo process, comprising the following steps of:

• transmitting an inversion pulse after the transmission of an excitation pulse;
• applying a phase encoding pulse to a phase axis;
• collecting data from echoes while applying a read pulse to a read axis;
• repeating the application of a rewind pulse to the phase axis plural times while changing the phase encoding pulse;
• collecting data from a plurality of echoes by one excitation;
• applying a pre-pulse to an arbitrary gradient axis before an excitation pulse;
• and
• adding the amount of correction for correcting a phase error caused by the pre-pulse to the initial phase encoding pulse or the initial rewind pulse.

A phase error measuring method, comprising the following steps of:

• (1) applying a pre-pulse to an arbitrary gradient axis, transmitting an excitation pulse, transmitting a first inversion pulse, subsequently transmitting a second inversion pulse, applying a dephaser pulse to a phase axis, collecting data from echoes while applying a read pulse to the phase axis, applying a rephaser pulse, subsequently transmitting a third inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, and determining the amount of a phase error, based on the collected data;
• (2) applying a pre-pulse to an arbitrary gradient axis, transmitting an excitation pulse, transmitting a first inversion pulse, applying a phase encoding pulse to a phase axis, applying a rewind pulse to the phase axis, subsequently transmitting a second inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, applying a rephaser pulse, subsequently transmitting a third inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, and determining the amount of a phase error, based on the collected data;
• (3) applying a pre-pulse to an arbitrary gradient axis, transmitting an excitation pulse, transmitting a first inversion pulse, applying a phase encoding pulse opposite in polarity to said (2) to a phase axis, applying a rewind pulse to the phase axis, subsequently transmitting a second inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, applying a rephaser pulse, subsequently transmitting a third inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, and determining the amount of a phase error, based on the collected data;
• (4) applying a pre-pulse opposite in polarity to said (1) to an arbitrary gradient axis, transmitting an excitation pulse, transmitting a first inversion pulse, subsequently transmitting a second inversion pulse, applying a dephaser pulse to a phase axis, collecting data from echoes while applying a read pulse to the phase axis, applying a rephaser pulse, subsequently transmitting a third inversion pulse, applying a dephaser pulse to the phase axis, collecting data from echoes while applying a read pulse to the phase axis, and determining the amount of a phase error, based on the collected data;
• and
• (5) determining the amount of a phase error caused by the pre-pulse, based on the amount of the phase error obtained from each of said (1) to (4).

An MRI system comprising:

• RF pulse transmitting means;
• gradient pulse applying means;
• NMR signal receiving means;
• said MR system executing MR imaging by a high-speed spin echo process for controlling said respective means to thereby transmit an inversion pulse after the transmission of an excitation pulse, apply a phase encoding pulse to a phase axis, collect data from echoes while a read pulse is being applied to a read axis, repeat the application of a rewind pulse to the phase axis plural times while changing the phase encoding pulse and collect data from a plurality of echoes by one excitation;
• pre-pulse applying means for applying a pre-pulse to an arbitrary gradient axis before the excitation pulse;
• and
• pre-pulse correcting means for applying a correction pulse for correcting a phase error caused by the pre-pulse to the phase axis before or behind the initial inversion pulse or adding the amount of correction for correcting the phase error caused by the pre-pulse to the initial inversion pulse.

An MRI system comprising:

• RF pulse transmitting means;
• gradient pulse applying means;
• NMR signal receiving means;
• said MR system executing MR imaging by a high-speed spin echo process for controlling said respective means to thereby transmit an inversion pulse after the transmission of an excitation pulse, apply a phase encoding pulse to a phase axis, collect data from echoes while a read pulse is being applied to a read axis, repeat the application of a rewind pulse to the phase axis plural times while changing the phase encoding pulse and collect data from a plurality of echoes by one excitation;
• pre-pulse applying means for applying a pre-pulse to an arbitrary gradient axis before the excitation pulse;
• and
• pre-pulse correcting means for adding the amount of correction for correcting a phase error caused by the pre-pulse to the initial phase encoding pulse or the initial rewind pulse.