Dielectric inserts for sensitivity and RF magnetic field enhancement in NMR volume coils.

A method for enhancing the signal to noise ratio (SNR) in NMR volume coils is described. By introducing inserts made of low-loss, high dielectric constant material into specific locations in the coil, the SNR can often be enhanced by up to 20%, while B(1) homogeneity is hardly affected. A model for predicting the limit of the SNR improvement is also presented. The model accurately predicts the SNR gain obtained in both numerical simulations and experiment. An experiment was conducted on a mini-MRI system. Experimental results are in very good agreement with the simulations in regard to both SNR improvement and B(1) enhancement in transmission. Inserts made of ultra high dielectric constant materials can be as thin as few millimeters, thus, conveniently fitting into existing coil-sample gaps in volume coils.