DESIGN AND ANALYSIS OF MICROCOILS FOR NMR MICROSCOPY

The signal-to-noise ratio achieved in a nuclear magnetic-resonance mic roscopy experiment is directly related to the performance of the radio frequency coil. An accurate determination of coil performance requires that the resistance of the coil be well characterized, Traditional hi gh-frequency electric-circuit models used to describe larger NMR coils are inadequate when the diameter of the conductor is reduced to the d imensions of the electrical skin depth (delta) at the frequency of ope ration. A more extensive model based on a scaling parameter that inclu des delta is presented. This model complements other existing circuit models that represent sample losses, ground-loop and parasitic losses, and the signal induced in the RF coil. Experimental verification is a ccomplished using a series of solenoidal microcoils in H-1 NMR microsp ectroscopy experiments at 4.7 T (200 MHz). This study demonstrates for the first time that a predictable performance enhancement is achieved using microcoils as small as 50 mu m in diameter. (C) 1995 Academic P ress, Inc.