Technical Advances for Sodium Magnetic Resonance Imaging

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Magnetic Resonance Imaging (MRI) is a core modern health care technology that provides unparalleled non-invasive images of the human body reflecting underlying structure, function, and metabolism in various organs. Over the last 35 years, university-based engineering advances in hardware, software and imaging physics have greatly increased the quality and capability of MRI. Routine clinical MRI acquires signal from the two hydrogen nuclei (1H) in the water molecule, of which we are primarily composed. However, water MRI cannot not detect all abnormalities. Our solution is to enable MRI image acquisition from other chemical elements important for proper cell functioning and health, like sodium (23Na). Note that the MRI physics of 23Na is considerably more complicated than that of 1H. Over the last 20 years, we have been developing sodium MRI with a focus on the brain (for stroke and multiple sclerosis) and cartilage (for osteoarthritis). The proposed NSERC Discovery grant is to advance MRI technology to image sodium in the skin. Salt (or sodium) in diet plays a key role in health, particularly as it relates to the "silent killer" hyper-tension (i.e. high blood pressure), which is far too prevalent in Canada and world-wide. Although one can measure sodium levels in a blood sample, this does not show how much sodium is accumulated in various tissues throughout the body. In fact, it has recently been discovered that skin (the largest organ of the body) is a major reservoir for excess sodium. International non-invasive studies with sodium MRI (usually of the human calf) has shown that skin sodium is elevated in men, aging, hypertension, obesity and clinical conditions such as diabetes, heart failure, and kidney disease. Although these results demonstrate promising utility for sodium MRI, the imaging methods used in these studies were simply borrowed from 1H MRI, and their low resolution images yield large errors in sodium level estimation. Our primary research goal is to enable accurate sodium concentration through novel engineering development specifically tailored for sodium MRI of the skin, which is challenging given how thin it is (only 1-2 mm thick). High-resolution images (like 4K television screens) are necessary, but this requires the design and construction of more sensitive MRI hardware (antennas), as well as inventing and optimizing new sodium-specific image acquisition software. These technology advancements will be guided by both computer simulation and experimental measurements. These optimal sodium MRI methods will be used to measure sodium concentrations in the skin (calf) of healthy individuals over a wide age range (children to the elderly), both males and females. This will establish a new `normative' basis for future comparisons to people with disease. Our sodium MRI advancements will also be made publicly and freely available for use by groups world-wide to improve their studies.