This thesis describes the development of both hardware and software techniques that increase the sensitivity and resolution of the magnetic resonance imaging experiment. Theoretical calculations of the sensitivity of the NMR experiment are performed and new results presented. A quantitative description of the sources of signal and noise in NMR allows the sensitivity of the NMR experiment to be improved. Methods of improving the sensitivity and resolution of the magnetic resonance Fourier imaging experiment are explored in terms of the pulse sequence parameters, k-space data acquisition, radiofrequency coils, gradient coils and digitization of the NMR signal. Techniques are presented to improve the sensitivity and resolution of the imaging experiment in each of these areas.
The methods described are applied to two different biological systems: articular cartilage and breast. In this thesis the study of articular cartilage will be exclusively in-vitro whereas the study of human breast tissue will be in-vivo. The results of these experiments demonstrate that the magnetic resonance imaging experiment may be improved to generate images with both high resolution and high signal-to-noise ratio even in systems with inherently low sensitivity. Such images, because of the large number of signal and contrast mechanisms in magnetic resonance imaging, provide information regarding the state of the tissue in question. This information has historically been primarily anatomic. This thesis demonstrates anatomic detail previously not demonstrated with in-vivo proton MRI. Information provided by these images allows greater diagnostic sensitivity and specificity for non-invasive diagnosis of breast pathology. Functional information provided by MRI has historically been based primarily on proton relaxation mechanisms. This thesis demonstrates, with sodium MRI, anatomic detail close to that of high resolution proton MRI. In addition, with short echo single quantum and triple quantum sodium imaging, the proteoglycan distribution in the cartilage may be assessed. This provides information which may constitute a functional assessment of the cartilage and may be useful to detect the early changes of osteoarthritis.
