Sodium MR Neuroimaging

Abstract

Sodium MR imaging has the potential to complement routine proton MR imaging examinations with the goal of improving diagnosis, disease characterization, and clinical monitoring in neurologic diseases. In the past, the utility and exploration of sodium MR imaging as a valuable clinical tool have been limited due to the extremely low MR signal, but with recent improvements in imaging techniques and hardware, sodium MR imaging is on the verge of becoming clinically realistic for conditions that include brain tumors, ischemic stroke, and epilepsy. In this review, we briefly describe the fundamental physics of sodium MR imaging tailored to the neuroradiologist, focusing on the basics necessary to understand factors that play into making sodium MR imaging feasible for clinical settings and describing current controversies in the field. We will also discuss the current state of the field and the potential future clinical uses of sodium MR imaging in the diagnosis, phenotyping, and therapeutic monitoring in neurologic diseases.

FIG 1.

A, MR imaging of a 38-year-old male patient with an IDH-mutated glioblastoma, World Health Organization grade IV. The tumor (white arrows) shows focal contrast enhancement in the T1-weighted image and is clearly depicted in the FLAIR image. Sodium imaging shows increased TSC. B, MR imaging of a 78-year-old male patient with an IDH wild-type anaplastic astrocytoma, World Health Organization grade III, in the right basal ganglia. The tumor (white arrows) shows focal contrast enhancement in the T1-weighted image and diffuse abnormalities in the FLAIR image. Sodium imaging shows no abnormality. Adapted and reproduced with permission from Shymanskaya et al.

FIG 2.

Images of a representative section from a patient with ischemic stroke showing the hypoperfused (time-to-maximum + 4 seconds) perfusion maps, the DWI with a DWI-hyperintense core in the dotted outline, the PWI-DWI mismatch tissue (penumbra) in the solid outline, and sodium images for (A) 4 and (B) 25.5 hours after the onset. This patient had a perfusion/diffusion mismatch at the first time point. The absolute lesion volume of the core enlarged from the first to the second time point, while the penumbral volume diminished. Note that the sodium signal is not increased in the first time point, while the high sodium signal is matched with DWI hyperintensity at the second time point. Adapted and reproduced with permission from Tsang et al.

FIG 3.

A patient with a cortical malformation. The TSC map shows high value on a cortical malformation that is subtle on high-resolution proton 3D-T1-weighted image (arrows) (adapted and reproduced with permission from Ridley et al). However, the effect of the partial volume effect should be examined in a future study with the achievement of higher-resolution sodium MR imaging.