3D radial projection technique with ultrashort echo times for sodium MRI: Clinical applications in human brain and skeletal muscle

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Abstract
23Na MRI has the potential to noninvasively detect sodium (Na) content changes in vivo. The goal of this study was to implement 23Na MRI in a clinical setting for neurooncological and muscular imaging. Due to the biexponential T2 decay of the tissue Na signal with a short component, which ranges between 0.5–8 ms, the measurement of total Na content requires imaging techniques with echo times (TEs) below 0.5 ms. A 3D radial pulse sequence with a TE of 0.2 ms at a spatial resolution of 4 × 4 × 4 mm3 was developed that allows the acquisition and presentation of Na images on the scanner. This sequence was evaluated in patients with low‐ and high‐grade gliomas, and higher 23Na MR signals corresponding to an increased Na content were found in the tumor regions. The contrast‐to‐noise ratio (CNR) between tumor and white matter increased from 0.8 ± 0.2 to 1.3 ± 0.3 with tumor grade. In patients with an identified muscular 23Na channelopathy (Paramyotonia congenita (PC)), induced muscle weakness led to a signal increase of ∼18% in the 23Na MR images, which was attributed to intracellular Na+ accumulation in this region. Magn Reson Med 57:74–81, 2007.