Poster — Thur Eve — 24: Variable Field Strength MR System for Hyperpolarized Noble Gas Imaging of Rodent Lungs

Abstract

The optimum field strength for hyperpolarized noble gas lung (129Xe and 3He) imaging depends on the sample/coil size and field‐dependence of the lung properties (i.e. relaxation times, susceptibility effects), and has been predicted to correspond to low field strengths (0.05–0.2T) for clinical studies. For the case of the small coils typically used for rodent lung imaging, it has been previously shown that the maximum SNR is expected to be at high fields (>3T). However, the SNR advantage of higher fields for rodent lung imaging can potentially be offset by improved coil design using Litz wire coils resulting in comparable SNR at low fields. In this work, a broad‐band variable field (0.01–0.15T) MR system is described, as well as experiments to validate the hyperpolarized noble gas image SNR dependence on field strength. The coil performance at 0.866MHz and 2.385MHz, corresponding to 129Xe and 3He frequencies at 73.5mT respectively, was optimized using multi‐turn Litz wire coils. The 129Xe and 3He image SNR of rat lung was investigated theoretically and in vivo, at 73.5mT and compared to images obtained at 3 T. Due to the improvement provided by the multi‐turn Litz coils, the SNR at 3T was predicted to be a factor of two higher compared to 73.5mT, this compares to a factor of about ten for single‐turned copper coils. In conclusion, hyperpolarized noble gas lung image quality in rats is comparable between 73.5mT and 3T, with the use of Litz wires together with the long T2* available at low magnetic field strength.