Abbreviations MRImagnetic resonance imaging SNR signal-to-noise ratio AbstractA method for quantifying the Tissue Sodium Concentration (TSC) in the rat brain from 23 Na-MR images was developed. TSC is known to change in a variety of common human diseases and holds considerable potential to contribute to their study;however, its accurate measurement in small laboratory animals has been hindered by the extremely low signal to noise ratio (SNR) in 23 Na images. To address this, the design, construction and characterisation of a double-tuned 1 H/ 23 Na dual resonator system for 1 H-guided quantitative 23 Na-MRI is described. This system comprised of an SNR-optimised surface detector coil for 23 Na image acquisition, and a volume resonator producing a highly-homogeneous B 1 field (<5% inhomogeneity) for the Na channel across the rat head. The resonators incorporated channel-independent balanced matching and tuning capabilities with active decoupling circuitry at the 23 Na resonance frequency. A quantification accuracy of TSC of < 10mM was achieved in Na-images with 1.2µl voxel resolution acquired in 10 minutes. The potential of the quantification technique was demonstrated in an in vivo experiment of a rat model of cerebral stroke, where the evolution of the TSC was successfully monitored for 8 hours after the stroke was induced.

The tightest bandwidth limits in ZTE arise from background signal and radiofrequency (RF) switching transients. Significant advances in ZTE performance will be afforded by faster transmit-receive (T/R) switching with negligible transients and RF coils free of background signal.