This thesis presents the design, implementation and testing of magnetic resonance imaging (MRI) sequences using spiral readout gradients. Three different designs and their corresponding sequences are developed: 14-interleaf, short readout, 4-interleaf, medium readout; and single-shot, long readout. The sequences are run in both 2D multislice and 3D modes. Image reconstruction is performed using regridding, together with three different spiral density compensation methods. / Results are compared for both phantom and in vivo human brain data. They indicate that the medium and long readout scans suffer from a certain level of image distortion due to field inhomogeneities, as well as T2* decay, in relation to their longer data acquisition times. This distortion is improved using a conjugate phase reconstruction technique, based on field maps generated from the same sequences. / Custom software was developed to design the spiral gradients, set-up the sequences and reconstruct images. This software is flexible, and can support a variety of scan parameters, taking into consideration the limitations of a given MRI scanner.

Magnetic resonance imaging (MRI) can be used to image diffusion in liquids, such as water in brain structures. Molecular diffusion can be isotropic or anisotropic, depending on the fluid's environment, and can therefore be characterized by a scalar, D, or by a tensor, D, in the respective cases. For anisotropic environments, the eigenvector of D corresponding to the largest eigenvalue indicates the preferred direction of diffusion. / This thesis describes the design and implementation of diffusion tensor imaging on a clinical MRI system. An acquisition sequence was designed and post-processing software developed to create diffusion trace images, scalar anisotropy maps, and anisotropy vector maps. A number of practical imaging problems were addressed and solved, including optimization of sequence parameters, accounting for flow effects, and dealing with eddy currents, patient motion, and ghosting. Experimental validation of the sequence was performed by calculating the trace of the diffusion tensor measured in various isotropic liquids. The results agreed very well with the quantitative values found in the literature, and the scalar anisotropy index was also found to be correct in isotropic phantoms. Anisotropy maps, showing the preferred direction of diffusion, were generated in human brain in vivo. These showed the expected white matter tracts in the corpus callosum.

The stringent demands for accuracy in radiosurgery impinge on all aspects of the radiosurgical procedure. A computer program, used to determine target coordinates from planar stereotactic image pairs, has been developed. Digital subtraction angiography images, obtained with a localizer attachment affixed to the stereotactic frame, are analyzed with the program for the localization of certain malformations. During treatment set-up verification, the center of the radiation distribution is determined using portal linear accelerator images of the collimated radiosurgery beam, with the patient in the final treatment position and without removal of the radiosurgical collimator. A custom portal localizer attachment has been developed in-house for this purpose. Localization results obtained with a test phantom show a maximum deviation of 0.4 mm from the known target locations. The program has also been shown to be effective in detecting a misalignment between a localized target and the treatment radiation center during set-up verification.

Following a departmental expansion, an isocentric cobalt-60 external beam teletheraphy unit was modified to produce a large fixed field for total body irradiation. The sourcehead was separated from the gantry and installed at a distance of 251.2 cm from the floor. The collimator was removed and replaced with a custom built secondary collimator projecting a 277 x 132.6 cm 2 radiation field at floor level. The work presented in this thesis describes the measurements performed to bring the unit into clinical use for total body irradiation. A custom flattening filter was placed below the secondary collimator to flatten the beam to within +/-3% of the central axis dose as measured at 10 cm in water. Percent depth dose, tissue-phantom-ratios, surface dose and absolute output were measured in the radiation field. The effects of inhomogeneities were studied and the thickness of lead used for lung attenuators was determined. Verification of treatment planning and delivery was performed with an Alderson-Rando anthropomorphic phantom and showed dose uniformity within +/-10% of the prescribed dose when a lead attenuator was used over the lung.

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4629. Adviser: Sharmila Majumdar.

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4640. Adviser: Sarah J. Nelson.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7341. Adviser: John A. Katzenellenbogen. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of California, San Francisco, 2006. / Source: Dissertation Abstracts International, Volume: 67-05, Section: B, page: 2685. Adviser: Daniel B. Vigneron.

Thesis (Ph.D.)--University of California, San Francisco with the University of California, Berkeley, 2006. / Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4549. Adviser: Sarah J. Nelson.

Thèse (Ph.D.)--Université de Sherbrooke (Canada), 2007. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.