Understanding and Optimizing Dynamics in Hyperpolarized Magnetic Resonance

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2021

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Magnetic resonance techniques are among the most powerful methods for characterization. However, they inherently suffer from an intrinsically low signal-to-noise due to the weak interaction of the nuclear spin with external magnetic fields. Hyperpolarization methods circumvent this limitation by deriving non-equilibrium spin polarization from an external source of spin order, dramatically increasing the magnetic resonance signals. Signal Amplification By Reversible Exchange, or SABRE, is a relatively new and promising method that derives spin hyperpolarization from parahydrogen, the singlet spin isomer of dihydrogen, allowing it to operate at a fraction of the cost of other hyperpolarization methods. A target molecule and parahydrogen transiently bind an organometallic complex, during which time polarization is transferred from the parahydrogen to target nuclei. The reversible nature of this interaction makes the hyperpolarization method readily scalable, giving SABRE the potential to supplant older, more expensive techniques and bring hyperpolarization technology to a broader audience. However, the current demonstrations of SABRE generate polarizations that are about an order of magnitude away from the upper theoretical limits of the technique, and variants of this experiment have been limited in target scope by the underlying physics. To address these limitations, this dissertation returns to examine the theoretical underpinnings of SABRE, and in doing so re-interrogates the unification of chemical exchange and quantum dynamics. We derive exact formulations of the chemical exchange interaction in both the magnetic resonance limits, which is used to construct a physically exhaustive computational model for SABRE. This model then facilitates in silico exploration of the system and permits us to address experimental limitations of the method. In particular, this dissertation utilizes simulations to develop and expand the capabilities of SABRE performed at arbitrarily high magnetic fields. We show that the limitations in the scope of SABRE imposed by the spin physics under these conditions may be removed, culminating in the first demonstration of simultaneous hyperpolarization of multiple components. This expansion is a key step towards translating SABRE into areas of conventional magnetic resonance such as biomolecular NMR and metabonomics. The theoretical framework presented here provides access to new routes for optimizing SABRE hyperpolarization, and we demonstrate that sequences may be developed to generate up to a five-fold increase in performance. Finally, we extend the theoretical treatment of chemical exchange within the Lindblad formalism to obtain exact master equations that are valid in any physical limit.

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Lindale, Jacob Ryan (2021). Understanding and Optimizing Dynamics in Hyperpolarized Magnetic Resonance. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/24378.

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