| It is well known that in the presence of radiofrequency (RF) irradiation, spin magnetization has different relaxation properties from T1 and T2. In the rotating reference frame, the component of the magnetization parallel to the effective field has a characteristic relaxation time T1rho. Like T1, T1rho varies, or disperses, with field strength because of energy exchange with the lattice. In MR imaging, T1rho contrast is useful because slow frequency components of the lattice are RF amplitude-dependent relaxation mechanisms.;The objective of this thesis is the technical development of T1rho MRI techniques for rapid T1rho quantification with low deposition of radiofrequency energy and the evaluation of these techniques in a set of patients with early cartilage degeneration. Three techniques are presented. Two techniques make use of the magnetization preparation and image acquisition paradigm and the third describes the development of a new steady-state technique. In Chapters 2 and 3 techniques to compensate for the heterogeneity of the static and RF fields are illustrated. Chapter 4 describes a fast imaging approach to T1rho MRI and makes use of a magnetization preparation step followed by a rapid multiecho acquisition sequence. In the last chapter of the Section I, Chapter 5, the development of a new technique which integrates the T1rho contrast generating mechanism with the acquisition sequence is detailed. The physics of the sequence are simulated and demonstrated experimentally in the motional narrowing regime and shown preliminarily in biological tissues.;One application for which T1rho MRI shows considerable diagnostic promise is the evaluation of cartilage degeneration in osteoarthritis. In Chapter 6, the conventional diagnostic techniques are reviewed and their limitations for determination of early biochemical change are qualified. Three techniques to evaluate cartilage degeneration, sodium MRI, the delayed gadolinium enhanced magnetic resonance imaging of cartilage (dGEMRIC) and T1rho MRI, are discussed at length. In Chapter 7, the fast imaging approach developed in Chapter 4 is used to assess the reliability of T1rho quantification of early grade 1 and 2 Outerbridge cartilage degeneration as determined by the arthroscopic gold standard. Future directions for research are briefly explored briefly in Chapter 8. |
