High spatial resolution ²³ Na-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.