Selective saturation in magnetization transfer experiments.
The concept of magnetic saturation in single and binary spin systems is essential to the understanding of magnetization transfer experiments. This paper outlines the requirements for selective magnetic saturation of either of two spin pools contained in a mixture, both having identical chemical shifts. Following a brief discussion of saturation in a homogeneous sample, simple relationships are derived that predict the maximum degree of selective saturation in a two-spin nonexchanging system. Optimal saturation conditions are described in terms of the intrinsic relaxation parameters as well as the experimental conditions of saturation offset frequency and amplitude. In addition, a novel method is proposed that may be applied to saturate the "free" water as opposed to the "bound" water spins in a magnetization transfer experiment. Saturation in an exchanging system is well approximated by these relationships under some physiologically relevant conditions, examples of which are provided. Application of the relationships presented may be useful in the design of experiments to produce maximum magnetization transfer contrast.
McGowan
J C
JC
Department of Radiology, University of Pennsylvania School of Medicine, Philadelphia.
Leigh
J S
JS
D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008962:Models, Theoretical