Nuclear magnetic resonance microscopy: New theoretical and technical developments
Zhou, Xiaohong
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Permalink
https://hdl.handle.net/2142/23736
Description
Title
Nuclear magnetic resonance microscopy: New theoretical and technical developments
Author(s)
Zhou, Xiaohong
Issue Date
1992
Doctoral Committee Chair(s)
Lauterbur, Paul C.
Department of Study
Chemistry, Physical
Engineering, Biomedical
Health Sciences, Radiology
Discipline
Chemistry, Physical
Engineering, Biomedical
Health Sciences, Radiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Engineering, Biomedical
Health Sciences, Radiology
Language
eng
Abstract
This dissertation describes some new developments in the theory, instrumentation and applications of nuclear magnetic resonance (NMR) microscopy. The purpose of this study is to theoretically analyze resolution limits in NMR microscopy and develop experimental techniques to achieve the highest possible spatial resolution for a variety of biomedical applications.
In the theoretical analysis, resolution limits due to linewidth broadening, unbounded diffusion and signal-to-noise ratio were evaluated for both projection reconstruction and Fourier transform imaging techniques. The results indicate that projection reconstruction gives a higher signal-to-noise ratio and requires a smaller magnetic field gradient to overcome the resolution limit due to linewidth broadening.
Experimentally, three-dimensional projection reconstruction techniques were employed to achieve the optimal spatial resolution with isotropic voxels. Using a custom-built NMR microscope, isotropic voxels as small as (6.4 $\mu m)\sp3$ were achieved on phantoms and tissue specimens. With this resolution, we have investigated the natural contrast phenomenon in fixed human brain tissue from the putamen and correlated the microscopic NMR images with the optical micrographs. Results obtained from this study clearly demonstrate that tissue structures, such as fiber tracts and capillary blood vessels, are well resolved in NMR images with endogenous $T\sb2$ contrast. Correlation between the microscopic NMR images and optical micrographs greatly assisted in the interpretations of the complicated tissue structures. We have also studied the effect of a contrast agent (dextran magnetite) on microscopic NMR images of fresh rat liver and spleen tissues and shown the importance of contrast agents in detecting microscopic tissue structures.
To extend NMR microscopy to in vivo studies, an instrument using surface RF coils was developed. Performance of a set of surface coils spanning from 6 mm to 43 mm were theoretically evaluated and experimentally verified on phantoms with the same sample-loss as tissues. Both theoretical and experimental results indicate that isotropic resolution of the order of (50 $\mu m)\sp3$ is possible in the regions close to the surface ($\sim2\ cm)$ of an object under in vivo conditions.
Several technical problems in NMR microscopy, including gradient-induced vibrations, slow motion, magnetic susceptibility artifacts, and extra echoes, were also discussed and solutions to minimize these problems were proposed and tested.
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