Sodium MRI techniques and applications to acute reperfused myocardial infarction.

摘要

The primary aims of this thesis include the developments of direct sodium MRI on a clinical scanner and the application of the technique on the quantification of absolute sodium levels in skeletal and heart muscle in health and disease.; First, a specialized type of a multinuclear phased array is designed and implemented to enhance signal-to-noise ratio (SNR) values in spoiled gradient recalled metabolic images of nuclei such as sodium (23Na) and phosphorus (31P). The array produced SNR improvements of 20% relative to the best positioned single coil, but gains of 300–400% were realized in many voxels located outside the effective field-of-view of the single coil.; Next, a novel reconstruction-restoration algorithm is proposed to enhance the low resolution 23Na MRI using a priori information. The performance of the algorithm is assessed by simulations, MRI of phantoms and by surface coil 23Na MRI studies of canine myocardial infarction on a clinical scanner where the injury was not evident at 1H MRI. The scatter in the area and amplitude measurements of ischemia-associated hyperenhancement in 23Na MRI was reduced demonstrating its ability to substantially improve quantification of the extent and intensity of metabolic changes in injured tissue, not evident by 1H MRI.; In an effort to combine the advantages of increased SNR of the phased-array and increased resolution of the restoration algorithm, yet capturing the fast T₂ 23Na components in tissue in vivo, a 3D 23Na twisted projection imaging (TPI) technique is implemented and applied on normal human skeletal muscle. The TPI technique and reconstruction and analysis tools are applied to assess whether absolute sodium levels measured noninvasively by 23Na MRI from infarcted canine hearts can be used to differentiate normal from acutely infarcted canine myocardium. (Abstract shortened by UMI.)