Temperature Dependence of the Chemical Shift of Lipid-dissolved 129Xe and Its Applications in MR Thermometry Public Deposited

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  • March 21, 2019
  • Zhang, Le
    • Affiliation: College of Arts and Sciences, Department of Applied Physical Sciences, Materials Science Graduate Program
  • The ability to measure tissue temperature non invasively and in vivo is critical to a number of applications, including the monitoring of thermal therapy in cancer patients. The resonance frequency of water protons is the most commonly used probe to measure relative temperature changes with MRI. The water proton resonance frequency (PRF) shifts linearly with temperature with a coefficient of -0.01ppm/°C for almost any tissue type and is as a result suitable to measure relative temperature changes in vivo. It has also been suggested that PRF could be used for absolute temperature measurements if a temperature independent resonance frequency, like that of neighboring fat spins (methylene protons), could be used to remove the effect of field drift and magnetic field inhomogeneities. Similarly, intermolecular zero-quantum coherences (iZQCs) between water and fat spins have also been suggested as a possible means of correcting for the effect of macroscopic susceptibility gradients at the microscopic scale, a scale much smaller than that typically probed by MRI. However water and fat do not mix and water and fat tissues have very different magnetic susceptibilities. In this thesis we analyze the effect of microscopic susceptibility gradient gener- ated at water-fat interfaces on fat-referenced PRF thermometry methods and on iZQC water-fat thermometry methods. Specifically, by using a combination of simulations and high-resolution spectroscopic measurements, we show that by referencing the water resonance frequency to that of nearby methylene protons one could obtain very inaccurate temperature measurements. We also show that the impact of microscopic susceptibility gradients is even stronger on the iZQC water-fat resonance frequency, which probes into the difference in resonance frequencies between water and fat spins more heavily at water-fat interfaces, where microscopic magnetic susceptibility gradients the strongest. At the same time we investigate the temperature dependence of the chemical shift of lipid- dissolved 129Xe (LDX). We show that the temperature coefficient of LDX resonance frequency is 20-fold higher than that of water and it is linear within the most clinically-relevant temperature range (20∼45°C) used in thermotherapies. Since LDX and methylene protons reside in the same environment, the effect of both macro and microscopic susceptibility gradients can be completely removed by referencing LDX to the nearby methylene protons, providing the opportunity to measure absolute temperature. We validated this method both in vitro and in vivo in rodents. We then applied this method in humans to directly measure the temperature of brown adipose tissue, which is a type of adipose tissue with clinical significance.
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  • In Copyright
  • Washburn, Sean
  • Lu, Jianping
  • Wu, Yue
  • Yuan, Hong
  • Branca, Rosa Tamara
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2017

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