High spatial resolution 23Na-MRI for ischemic brain injury detection.

High spatial resolution sodium (23Na) imaging of brain lesions remains challenging due to the intrinsically low signal-to-noise ratio (SNR) of 23Na-MRI compared with conventional proton (1H) MRI. In this study, we established a high-resolution 23Na-MRI platform based on 14 T preclinical scanner using a dual-tuned head-implanted RF coil. This configuration enables the acquisition of 1H-based T2-weighted anatomical and diffusion-weighted imaging (DWI), as well as 23Na-MRI, from the same animal. Brain-wide 23Na-MRI with 300×300 μm2 in-plane resolution was performed within the first 4 hours after acute middle cerebral artery occlusion (MCAO) induced ischemic stroke induction. Hyperintense 23Na-MRI signals were observed in the ischemic brain regions, presenting a contrast-to-noise ratio (CNR) that exceeded that of T2-weighted images. Infarct regions can be well-identified in the elevated 23Na signal, which is spatially consistent with regions of reduced apparent diffusion coefficient (ADC) values, indicating water restriction in the ischemic core. This work established implanted double-tuned 1H/23Na RF coils as a powerful approach for high-resolution 23Na-MRI readout, facilitating the early detection of ischemic brain injury.