Implementation Of ～(23)Na Magnetic Resonance Imaging

MRI is undoubtedly one of the most important contributions made by physiciststo the field of medicine. Nowadays MRI has become one of the most importanttechnology used in clinical diagnosis of diseases and basic research in all braches ofbiomedicine. There is no evidence showing that the static magnetic field, pulsedgradient field and radiofrequency(RF) pulses used in MRI have harmful effects onanimals or humans. It can provide high spatial resolution 2D and 3D images at anyslice orientation and real time information about biological systems with differentcontrasts. MRI examination is noninvasive so that it causes no damage to thesample/subject and enables longitudinal studies on the same sample/subject. Currentlyproton MRI, which detects the signal from tissue water, is the most widely used MRItechnique in the field of biomedicine. With the advances in MRI technology andincreased demands from practical applications, imaging with non-proton nuclei, suchas sodium, has attracted more and more research interests.Sodium is one of the most common electrolytes in biological organisms. Theextracellular sodium concentration is roughly 8 to 10 times of that in the intracellularspace. The sodium concentration gradient is tightly regulated by sodium-potassiumpumps, and plays very important roles in maintaining cellular integrity andfunctionality. Tissue sodium concentration is sensitive to pathological conditions andcan be used as an indicator for cellular integrity, tissue metabolic activity and ionhomeostasis. Using ²³Na MRI to measure the concentration and distribution of tissue sodium can provide lots of important biological information that is not obtainableusing ¹H MRI. However, tissue sodium concentration is much lower than water sothat it is often true that ²³Na MRI requires long acquisition time and can only yieldimages with low spatial resolution and low signal-to-noise ratio. Using higher fieldstrength magnets and high performance RF coils to image can partially ameliorate theaforementioned problems.The work described in this thesis is a set of exploratory experiments performedin attempt to implement, for the first time, ²³Na MRI in our laboratory. First, asingle-loop surface coil specially designed for ²³Na MRI was made by the followingsteps: 1) design a proper circuit for the surface coil based on the principlessummarized by others; 2) the validity of the design was proven by experiments; 3)choose appropriate non-magnetic materials (i.e., wire, capacitors and circuit board) tofabricate the coil; 4) summarize the problems encountered and experiencesaccumulated in making the coil. As the next step, we then use the coil to acquire ²³Nadensity-weighted images on tubes filled with NaCl solution, boiled salted quail eggand rat brain on a Bruker Biospec 47/30 MRI scanner. The studies represent the veryfirst step towards many ²³Na MRI application studies to come, especially in the fieldof biomedicine.