3D-multi-echo radial imaging of ²³ Na (3D-MERINA) for time-efficient multi-parameter tissue compartment mapping

This work demonstrates a 3D radial multi-echo acquisition scheme for time-efficient sodium (²³ Na) MR-signal acquisition and analysis. Echo reconstructions were used to produce signal-to-noise ratio (SNR)-enhanced ²³ Na-images and parameter maps of the biexponential observed transverse relaxation time ( T2*) decay.

A custom-built sequence for radial multi-echo acquisition was proposed for acquisition of a series of 3D volumetric ²³ Na-images. Measurements acquired in a phantom and in vivo human brains were analyzed for SNR enhancement and multi-component T2* estimation.

Rapid gradient refocused imaging acquired 38 echoes within a repetition time of 160 ms. Signal averaging of multi-echo time (TE) measurements showed an average brain tissue SNR enhancement of 34% compared to single-TE images across subjects. Phantom and in vivo measurements detected distinguishable signal decay characteristics for fluid and solid media. Mapping results were investigated in phantom and in vivo experiments for sequence timing optimization and signal decay analysis. The T2* mapping results were consistent with previously reported values and facilitated fluid-signal discrimination.

The proposed method offers an efficient ²³ Na-imaging scheme that extends existing ²³ Na-MRI sequences by acquiring signal decay information with no increase in time or specific absorption rate. The resultant SNR-enhanced ²³ Na-images and estimated T2* signal decay characteristics offer great potential for detailed investigation of tissue compartment characterization and clinical application. Magn Reson Med 79:1950-1961, 2018. © 2017 International Society for Magnetic Resonance in Medicine.