| Even before the development of magnetic resonance imaging, scientists and engineers repeatedly predicted that, despite the theoretical potential of high field, physical and engineering challenges would prevent the practical realization of gains in signal to noise. Many of the arguments used to disparage high field MRI can be divided into issues of uniform excitation, image distortion, and patient safety. In the former category lies challenges such as RF penetration limitations, dielectric resonances, coil self-resonance, coil-sample interactions, and RF power requirements, which may prevent uniform B1 can best be studied with numerical modeling techniques. Within the second category are effects such as chemical shift artifact, susceptibility distortions, and contrast convergence that can be well studied through analytic techniques and methodical manipulation of imaging parameters. In the category of safety belong RF power deposition and magnetohydrodynamic effects. In this thesis, issues of static field safety will be exhaustively explored and investigation of image contrast and quality will be undertaken to assess the potential of the 8 Tesla system for human neuroimaging. This thesis will specifically examine the theoretical risk of cardiac arrhythmia from induced currents and demonstrate the negligible cardiac, cognitive, and physiological bioeffects through animal and human studies. The extent of signal to noise ratio enhancement possible at 8 Tesla will be assessed and harnessed to obtain high resolution whole brain images. In the end, experimental results and analysis show that, despite the presence of artifact, high resolution images of the human brain with unique contrast can be safely obtained at 8 Tesla. |
