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Sodium MRI of the Human Brain |
There’s interest to image sodium non-invasively in human as the distribution of sodium and potassium ions are tightly regulated across cell membrane to generate a resting membrane potential. Under pathological conditions such as cerebral ischemia, the homeostatic condition is disrupted due to the failure of the active transport mechanism across cell membrane.
Even as sodium is the second most biological sensitive element detectable using NMR, imaging of sodium in vivo is very challenging. This is due to its smaller gyromagnetic ratio and a much lower concentration in vivo compared to hydrogen, which constitutes most of the clinical imaging techniques. MRI of sodium yields far inferior image quality and requires longer scan time than conventional MRI as seen in the images below. Therefore, sodium imaging has not been applied clinically.
In this project, I optimized a multiple quantum filtered MRI pulse sequence to image sodium in the human brain at 4.7-Tesla to maximize signal-to-noise ratio (SNR) under the constraint of specific absorption rate (SAR) within a clinically reasonable scan time. Specific sequence parameters were optimized by scanning a custom-built phantom and healthy volunteers. I published the first double-quantum filtered sodium image of the human brain and demonstrated potential utility of sodium imaging in acute stroke patients.
{% include image.html url="/assets/img/SodiumMRI/Subject 1 - TSC_cropped.png" description="Brain tissue sodium MRI of a healthy volunteer" %}
{% include image.html url="/assets/img/SodiumMRI/Subject 1 - TQ90deg_cropped.png" description="Brain triple-quantum sodium MRI of the same volunteer" %}