Type of Document Dissertation Author Cobb, Jared Guthrie Author's Email Address email@example.com URN etd-08262011-130202 Title Quantitative proton relaxometry in the rotating frame with magnetic resonance imaging Degree PhD Department Biomedical Engineering Advisory Committee
Advisor Name Title John C. Gore Committee Chair Bruce M. Damon Committee Member Daniel F. Gochberg Committee Member J. Christopher Gatenby Committee Member Mark D. Does Committee Member Keywords
- rotating frame
Date of Defense 2011-08-09 Availability unrestricted AbstractConventional magnetic resonance imaging (MRI) uses contrast that is weighted by the intrinsic tissue parameters T1, and T2. Contrast may also be generated in the rotating frame with the analogous time constants T1ρ or T2ρ. Traditionally T1ρ measurements have been used to investigate low frequency dipolar interactions in the kHz range. However, other biological processes, such as chemical exchange, also occur on this time scale. Recently it has been shown that these processes dominate R1ρ (1/T1ρ) relaxation at high field, and these interactions are of interest as high field imaging systems become increasingly common. We have developed quantitative spin-locking (SL) techniques to probe rotating frame relaxation on clinical and pre-clinical imaging systems. Experiments were performed with these techniques to generate T1ρ maps of pediatric epiphyseal cartilage and mouse brain.
If the power of the SL field is varied, the measured T1ρ values will change in a phenomenon known as T1ρ dispersion. These dispersion profiles vary with tissue properties such as pH and metabolite concentration, and the data may be fit with a model to extract unique parameters such as chemical exchange. Novel methods were developed to generate exchange rate based contrast using the contrast features of T1ρ dispersion profiles. A number of exogenous and endogenous contrast agents were quantitatively compared to chemical exchange saturation contrast (CEST) imaging. CEST and SL techniques were evaluated for their complementary features to determine the experimental conditions where each may be most appropriately used.
Diffusion processes were explored as an additional contributor to T1ρ dispersion. Various spherical phantoms of different size and material properties were measured with SL techniques to observe their effects on contrast. Methods were developed to separate the effects of diffusion and chemical exchange.
The experiments reported here further elucidate the contributing factors to R1ρ relaxation in a variety of biologically relevant molecules and tissues. Finally, the methods resulting from these experiments are useful for generating novel contrast that is primarily dependent on exchange rates.
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