Dynamics of the nuclear magnetic resonance COSY-revamped by asymmetric z-gradients (CRAZED) experiment

The nuclear magnetic resonance COSY-revamped by asymmetric z-gradients experiment has been applied to a wide range of problems from functional magnetic resonance imaging to structure determination in porous media. In this article, we investigate the temporal dynamics of the experiment in the regime where the linear approximation (gamma mu (0)M(0)t much less than 1) for the signal evolution is no longer valid. Numerical solutions of the nonlinear evolution equations were obtained with and without radiation damping and compared to previous analytical approximations to explore their range of validity. Experiments were performed on cyclohexane at 11.7 T, and the signal dependence on flip angle and modulation gradient strength investigated-under conditions where the effects of radiation damping were minimized. The analytical expressions were found to be valid only when diffusion effects are either negligible or when the characteristic time for diffusional attenuation is small compared to the dipolar demagnetizing time (k(m)(2)D much greater than gamma mu M-0(0)). Excellent agreement was obtained between the experimental data and the numerical solutions of the modified Bloch equations. (C) 2001 American Institute of Physics.