High frequency volume coils for clinical NMR imaging and spectroscopy

TLDR

The distributed circuit transmission line resonator was engineered for high‑frequency, large‑volume NMR imaging, using a tunable coaxial cavity and finite‑element Maxwell simulations to predict and correct B1 field homogeneity, and includes practical design guidance and quadrature driving techniques. The resonator delivers large head‑ and body‑sized volumes, high efficiencies, broad tuning up to 500 MHz, and demonstrates uncompromised high‑field signal‑to‑noise and spatial resolution in human head images at 175 MHz.

Abstract

Abstract A tuned transmission line resonator has been developed in theory and in practical design for the clinical NMR volume coil application at 4.1 tesla. The distributed circuit transmission line resonator was designed for high frequency, large conductive volume applications where conventional lumped element coil designs perform less efficiently. The resonator design has made use of a resonant coaxial cavity, which could be variably tuned to the Larmor frequency of interest by tunable transmission line elements. Large head‐ and body‐sized volumes, high efficiencies, and broad tuning ranges have been shown to be characteristic of the transmission line resonator to frequencies of 500 MHz. The B 1 homogeneity of the resonator has been demonstrated to be a function of the electromagnetic properties of the load itself. By numerically solving Maxwell's: equations for the fully time‐dependent B 1 field, coil homogeneity was predicted with finite‐element models of anatomic structure, and inhomogeneities corrected for. A how‐to exposition of coil design and construction has been included. Simple methods of quadrature driving and double tuning the transmission line resonator have also been presented. Human head images obtained with a tuned transmission line resonator at 175 MHz have clearly demonstrated uncompromised high field advantages of signal‐to‐noise and spatial resolution.