Line Scan Proton Magnetic Resonance Spectroscopic Imaging

This thesis explores magnetic resonance (MR) imaging methodologies that provide in vivo spectroscopic information. To date such information has not been routinely acquired and used in diagnosis. The general objective of the thesis is to develop and implement new and fast MR spectroscopic imaging techniques that can be practically utilized to study spectroscopic information in vivo. This thesis presents innovative line scan spectroscopic imaging methodologies based on spectroscopic interrogation of voxels along strategically oriented tissue columns. The techniques combine some of the most attractive features of both imaging and spectroscopic methods utilizing Carr-Purcell-Meiboom-Gill multiple-echo sequences, rapid acquisition and relaxation enhanced or equivalently fast spin echo sequences, inner-volume localization, and chemical shift imaging principles. The techniques offer a compromise between the low-spectral-resolution, high-spatial-resolution, large-volume-coverage imaging methods of Dixon and Sepponen and the high-spectral-resolution, single-voxel localized proton spectroscopic approaches. Developed and implemented on the conventional 1.5 Tesla clinical MR imaging scanner with standard software and hardware configurations, the non-invasive line scan spectroscopic imaging techniques generate spectroscopic images with high spatial, variable spectral resolution and adequate volume coverage in clinically useful time periods of 10 minutes or less. This thesis demonstrates the line scan spectroscopic imaging techniques in vivo. Spectral concentrations and relaxation times are obtained for bone marrow and brain metabolites. Specifically, quantification of water and saturated fat (concentration and T2 relaxation time) is performed on vertebral bone marrow in a group of healthy adult volunteers. Studies of developing bone marrow in knee are performed on a group of children and a group of adult volunteers. Furthermore, with variable spectral resolution and slightly modification, the techniques are shown applicable for quantification the lipid chemical composition. The applications include measurements of lipid spectral T1 relaxation time, detection of terminal methyl protons even with a limited spectral resolution, monitoring of degree of unsaturated fatty acid. In addition, the techniques are modified and applied to quantify and map human brain metabolites. The clinical feasibility of brain metabolite studies is illustrated in a group of healthy adult volunteers and a tumor patient. The techniques developed in this thesis promise many possible applications. One is to quantitatively study lipid spectra in bone marrow during and after radiation therapy and chemotherapy for patients with bone marrow diseases like leukemia. Another one is to study the evolution of cerebral metabolites within brain tumors to see how relative concentrations of MR observable metabolites correlate with the state of the tumors and the relative progress of various therapies. The other application is to study lipid metabolic disorders, such as cystic fibrosis. The techniques also provides the opportunities to perform dynamic chemical shift imaging studies in vivo. Thesis Supervisor: Gordon L. Brownell Title: Professor of Nuclear Engineering, MIT Thesis Supervisor: Robert V. Mulkern Title: Assistant Professor of Radiology, Harvard Medical School Thesis Reader: Sow-Hsin Chen Title: Professor of Nuclear Engineering, MIT Thesis Reader: David G. Cory Title: Assistant Professor of Nuclear Engineering, MIT Thesis Reader: Ferenc A. Jolesz Title: Associate Professor of Radiology, Harvard Medical School