High-Field Multinuclear MRI Reveals Sodium Relaxation Heterogeneity in Cortical Organoids.

Area of Science:

• Neuroscience
• Biomedical Imaging
• Biophysics

Background:

• Sodium ions are crucial for neural function, but imaging their microenvironments is challenging.
• Conventional proton (¹H) MRI lacks sensitivity to ionic changes, focusing on water and structure.
• Sodium magnetic resonance imaging (²³Na MRI) offers unique insights into ionic dynamics and tissue composition.

Purpose of the Study:

• To establish a high-field multinuclear MRI platform for imaging human cerebral organoids.
• To investigate the feasibility of quantitative sodium relaxometry in three-dimensional neural models.
• To characterize ionic microenvironments and relaxation behavior in cerebral organoids using ²³Na MRI.

Main Methods:

• Developed a high-field (14 Tesla) multinuclear MRI platform with a dual-tuned ¹H/²³Na radiofrequency coil.
• Performed co-registered structural, diffusion, and multi-echo ²³Na MRI on fixed human cerebral organoids.
• Utilized bi-exponential analysis to characterize sodium signal decay and relaxation components (T2*).

Main Results:

• High-resolution ¹H MRI revealed significant microstructural heterogeneity in organoids.
• Multi-echo ²³Na MRI enabled voxel-wise characterization of quadrupolar relaxation behavior.
• Identified distinct sodium relaxation components (T2*_short ≈ 1 ms, T2*_long ≈ 12 ms) and spatial heterogeneity.

Conclusions:

• Demonstrated the feasibility of quantitative sodium relaxometry in human cortical organoids.
• Established a powerful multinuclear MRI platform for studying ionic microenvironments in neural tissue models.
• Provides a foundation for investigating ionic dynamics in complex three-dimensional neural systems without systemic confounds.