deseree davisdeseree davis The proposed research aims to develop instrumentation which will improve the resolution of nuclear magnetic resonance (NMR) microscopy by at least an order of magnitude to the (1- 2 m)3 range. Since mammalian cells are typically 5-10 m in diameter, this advance would open up a whole range of subcellular applications which are currently precluded. The intrinsic advantages of NMR over other microscopic techniques include the ability to provide full three- dimensional information and its non-invasive character. NMR microscopy not only gives spatial information, but can also be used to determine chemical composition, proton mobility, and molecular diffusion, the latter two measurements giving information on the physical environment of the biological molecules of interest. The major innovation in this research will be the design and optimization of radiofrequency (RF) microcoils of diameter 100-200 m, an order of magnitude less than has previously been used in NMR microimaging applications. In addition to the intrinsic increase in signal-to-noise ratio (SNR) per voxel for a given voxel size, the use of small RF coils results in a lower acquisition bandwidth and further SNR improvements over larger coils. These RF coils will also allow the design and construction of very small diameter, high strength magnetic field gradients, which will be necessary to overcome diffusion and susceptibility effects and achieve the desired resolution. An integrated assembly of RF microcoil, magnetic field gradients, and micropositioner will be constructed. Filtered back projection (FBP) techniques will be used to acquire the data, since these have an intrinsically higher SNR than Fourier techniques, and require smaller gradients for a given resolution. The first experiments using the optimized imaging system will be to determine experimentally the maximum possible resolution by comparing competing theories of effects of molecular diffusion, the lowest detectable number of spins, and the effects of phenomena such as edge enhancement at non- permeable boundaries. These have not been rigorously studied previously since the sensitivity of the radiofrequency coils was not sufficiently high. Two major biological applications of the research are proposed. First, high resolution microimaging of excised spinal cord tissue. Non-invasive MRI has shown that signal intensity changes are produced by both spinal cord damage and subsequent regeneration. In order to understand these changes fully, it is necessary to look at the small structures within the cord, as opposed to a large volume averaged signal intensity from the whole cord. Second, we will use the microscopic radiofrequency and gradient coils to determine the presently unknown physical environment of protein-rich vesicles by two dimensional diffusion-ordered spectroscopy, information which should help to elucidate the action of certain neurotransmitters in mammals. The development of micro-NMR systems is an emerging area in imaging which should be fully integrated into our academic curriculum. Currently the applicant, together with his colleagues, have developed a unique series of three courses in magnetic resonance within the Department of Electrical and Computer Engineering. The major educational thrust will be to complete the integration of interactive computer based learning into these three courses, combined with the preparation of a laboratory based course on magnetic resonance systems to accompany a graduate level lecture series. The proposed research has many aspects which are relevant to electrical engineering: high frequency modelling and simulations, electrical circuit characterization, and design optimization, as well as applications which are of interest to the bioengineer. Indeed, since magnetic resonance is not usually an active area for electrical engineers, we anticipate that significant advances will be made by the inclusion of faculty, underg raduate and graduate researchers from this department. More than twenty students within the department have already chosen this area for undergraduate research and their Senior Design projects with the applicant in the past two years.
