Use of an optimal control algorithm for the design of MRI refocusing pulses with phase-free rotation axis

摘要

A method of designing a refocusing pulse (RRP) or pulse train (RPT) for Magnetic Resonance Imaging comprising the steps of:a) determining a performance criterion, called phase-free performance criterion, representative of a proximity between a rotation of nuclear spins induced by said pulse and at least a target operator, summed or averaged over one or more voxels of an imaging region of interest; andb) adjusting a plurality of control parameters of said pulse to maximize said phase-free performance criterion;wherein said or each said target operator is chosen such that said phase-free performance criterion takes a maximum value when the nuclear spins within all said voxels undergo a rotation of a same angle θ around a rotation axis lying in a plane perpendicular to a magnetization field B₀, called a transverse plane, with an arbitrary orientation;characterized in that said angle θ is different from Mπ radians, with integer M, preferably with θπ radians and even preferably with θ≤0.9·π radians.