The field dependence of NMR imaging. I. Laboratory assessment of signal‐to‐noise ratio and power deposition

Abstract
A method is proposed for measuring on the bench the NMR signal‐to‐noise ratio of rf probes, (over the range 1–100 MHz) and also the power deposited in patients during the imaging experiment. The technique is based on the principle of reciprocity, in that a direct relationship exists between the magnetic field generated (upon transmission) by a matched probe coil and the signal‐to‐noise ration delivered by the same coil when used as a receiver. The construction and use of a calibrated sense coil for measuring the field is described, and the precautions and theory necessary for accurate measurement and understanding are outlined. Finally, the method is verified by comparison with a direct spectral measure of sensitivity obtained from a small doped water sample placed in NMR imaging equipment. © 1986 Academic Press, Inc.

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