Advances in Single Point Imaging for Electron Paramagnetic and Magnetic Resonance Imaging.

摘要

Electron paramagnetic resonance imaging (EPRI) and magnetic resonance imaging (MRI) are non-invasive imaging modalities based on similar physical phenomenon. MRI provides rich anatomical information based on proton imaging, while EPRI offers unique, quantitative information using spin probes such as tissue oxygenation, acidity, and redox status. In EPR-oximetry due to extremely short EPR signal lifetime (< 1mus) of spin probe (e.g., Oxo-63) and hardware constraints (e.g., gradient slewrate and RF deadtime), common imaging schemes utilized in MRI are generally not applicable. Therefore, specialized imaging schemes must be utilized to allow encoding of the rapidly decaying signal in EPRI. In MRI, single point imaging (SPI) has been developed for imaging object with short T2* in 1985, and has recently been revisited as a hybrid technique to improve the imaging of short T2* species. In EPRI, SPI has shown utility for in vivo characterization of tissue oxygenation.;This thesis explores novel uses of SPI in EPR-oximetry and MRI. In EPR studies, a new method for image acquisition and reconstruction is studied, which enables accurate T2* estimation with high spatio-temporal resolution for oxygen imaging. Moreover, a method utilizing a model-based compressed sensing technique is explored to further accelerate image acquisition (up to 30x). In MR studies, a novel technique to measure a gradient waveform using dynamic SPI is developed, where a gradient impulse response function based on LTI concept is also studied. For improved imaging of short T2* species in MRI, a new imaging scheme using SPI is developed, termed ramped hybrid encoding (RHE), where encoding time is minimized to reduce blurriness in object with short T2*. Two applications based on RHE are studied in depth: a rapid RHE-based attenuation correction for PET/MR and a highly efficient bi-component T2* estimation in human knee using RHE.