Technique for compensating for patient motion in magnetic resonance

Abstract

In a magnetic resonance imaging system, object movement along an axis associated with readout magnetic gradient pulses is detected, quantized and compensated for in reconstructing an image slice. Phase-encoding magnetic gradient pulses in the sequence are arranged so that low-order phase-encoding pulses are distributed substantially uniformly during scanning time. In an N-slice acquisition, object movement is determined y arranging each of the N sets of phase-encoding gradient pulses comprising a multi-slice sequence such that at each scan time, at least one of the N sets contains a low-order phase-encoding gradient pulse. During data acquisition, echoes returned from low-order phase-encoding gradient pulses have sufficient signal-to-noise ratios to identify object position along the readout axis. Identification of object movement from one slice may be valid for other slices relatively adjacent physically in the object, so that all N slices are movement corrected during image reconstruction. Two-dimensional object position may also be identified and corrected by suitably exchanging the axes of N sets of pulses within a sequence. For a single slice acquisition, object position may be identified when scans associated with low-order phase-encoding gradient pulses are distributed evenly during imaging. After one-dimensional Fourier transformation, object position relative to a reference box function is determined using cross-correlation.