Huang Susie Y, Walls Jamie D, Wang You, Warren Warren S, Lin Yung-Ya
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA.
J Chem Phys. 2004 Oct 1;121(13):6105-9. doi: 10.1063/1.1802492.
Turbulent spin dynamics arising from the joint action of radiation damping and the distant dipolar field are shown to generate irreproducible measurements in popular high-field, gradient-based magnetic resonance (MR) experiments, undermining the prevailing assumption of essentially predictable observables in MR. Sizeable fluctuations in echo amplitudes are reported and numerically simulated for pulsed gradient spin echo and stimulated echo diffusion measurements. The underlying microscopic dynamical instability is characterized by analysis of the finite-time Lyapunov exponents. Perturbations to the modulated magnetization are shown to render magic-angle gradients ineffective in suppressing signal fluctuations. Alternative approaches are suggested for cancelling out the feedback interactions leading to spin turbulence.
研究表明,在流行的基于梯度的高场磁共振(MR)实验中,由辐射阻尼和远距离偶极场的联合作用产生的湍流自旋动力学导致测量结果不可重复,这削弱了MR中基本可预测可观测量的普遍假设。报告了脉冲梯度自旋回波和受激回波扩散测量中回波幅度的显著波动,并进行了数值模拟。通过对有限时间李雅普诺夫指数的分析,表征了潜在的微观动力学不稳定性。结果表明,对调制磁化强度的扰动会使魔角梯度在抑制信号波动方面失效。文中提出了替代方法,以消除导致自旋湍流的反馈相互作用。