Abstract:
Magnetic resonance (MR) studies are well established in numerous industrial, medical
and scientific applications. Examples include MR spectroscopy (MRS), which is utilized
for non-destructive chemical analysis, and MR imaging (MRI), which is a common noninvasive,
medical imaging technique with great contrast in soft tissue. Conventional
systems are bulky and expensive, because large magnet coils are utilized to generate
high magnetic fields and signal amplitudes. The project presented in this thesis seeks
to address these issues by combining the use of ultralow magnetic fields (ULF), with
two signal enhancing hyperpolarization techniques.
First, the experimental ULF-MR setup was established. It employs an open magnet
coil assembly in combination with a superconducting quantum interference device
(SQUID) as sensor, allowing for the quantitative measurement of the MR signal. Spectroscopic
signal amplification by reversible exchange (SABRE) experiments and Overhauser
dynamic nuclear polarization (ODNP) enhanced MRI showcased the successful
implementation of these hyperpolarization techniques, and the imaging capabilities of
the system. The results outline future applications and emphasize how the ultralowfield
approach benefits from enhanced signal amplitude by hyperpolarization methods,
while in turn facilitating the investigation and refinement of these techniques.
Next, the simultaneous SABRE enhanced measurement of fluor and proton spins
was performed. After investigating the influence of some measurement parameters on
signal enhancement, correlation spectroscopy was utilized for a more detailed examination
of the polarization transfer mechanisms. The studies demonstrated the capability
of the system to perform multinuclear correlation spectroscopy experiments and the
results are proof for the hyperpolarization of multiple-spin states by SABRE.
The last part of this thesis focused on ODNP. With this technique, free radicals can
facilitate an increase in nuclear spin polarization, enhancing the MR signal. Here, the
polarization transfer efficacy of a broad range of nitroxide radicals was characterized.
The comprehensive study allowed for a correlation of chemico-physical features with
hyperpolarization-related properties. The results provide a catalog of polarizing agents
and give direction for predicting and optimizing free radical performance in the future,
especially for the development of functionalized polarizing agents.
Reviewing the results allowed for a discussion of future utilization and direction
of research for both hyperpolarization techniques. While possible applications differ
greatly, they both share the prospect of profoundly enhancing MR signal and contrast
in not only ultralow-fields but also in higher field regimes.
Magnetic resonance imaging
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