Theoretical and experimental study of in vivo ultra-high resolution NMR imaging with surface gradient coil

Abstract

High resolution NMR imaging methods and experimental setups which can be applied to the existing NMR imaging and NMR spectroscopy systems are described. Limitations and requirements of the high resolution imaging are analyzed. An ultimate resolution and voxel size dependent signal-to-noise ratio in microscopic resolution imaging (NMR microscopy) are presented and experimentally verified. New pulse sequences which reduce both diffusiondependent resolution degradation and signal attenuation are developed and selection of optimal bandwidth and acquisition time for maximal SNR is described. A new surface gradient coil consisting of three orthogonal channels and a planar form is described. This coil has been developed for high-resolution imaging which generally requires strong gradient fields. The surface gradient coil can produce strong gradient fields with good linearity within a limited imaging region. To increase the signal-to-noise ratio, an integrated surface RF coilsurface gradient coil set is developed and experimentally examined. A design of threechannel surface gradient coil to improve the performances are also presented. The optimized new surface gradient coil provides wider linear field gradint region, removes rotational force and field offset, and reduces coupling between the surface gradient coil and combined surface RF coil. In this thesis, the geometrical structures and characteristics of the proposed surface gradient coil are discussed, and some experimental results obtained by use of the coil sets are presented. Microscopic images of water-filled phantoms and plant stems were obtained by using the developed imaging setups and the imaging methods. Localized high resolution images of water-filled phantoms and volunteer``s knee and spinal cord were obtained by using the surface RF coil-surface gradient coil sets.