Patent ID: 7224164
Filing Date: 2007-05-29
Classification: G01R

Abstract:
1. A method of correcting magnetic field drift in a magnetic resonance imaging apparatus, the method comprising: performing a first single shot EPI sequence in which a first excitation induces a following first magnetic resonance signal including a series of echoes with each of a series of different phase encodings including one of the echoes with zero phase encoding, the zero phase-encoded echo being timed to occur at a preselected time interval after the first excitation; determining a first phase of the first magnetic resonance signal at the preselected time interval after the first excitation; performing a second single shot EPI sequence in which a second excitation pulse induces a following second magnetic resonance signal including a series of magnetic resonance echoes with a series of different phase encoding, one of them with a zero phase encoding, the zero phase-encoded echo being timed to occur at said preselected time interval after the second excitation; determining a second phase of the second magnetic resonance signal at said preselected time interval after the second excitation; determining a difference between the first and second determined phases; from the determined phase difference, determining at least one of an adjustment to a frequency for excitation in a subsequent single shot EPI sequence and a magnitude of a main magnetic field adjustment.