Implementation of propeller, spiral, and variable density spiral methods for dynamic contrast enhanced magnetic resonance imaging.

摘要

Previous studies showed that dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is a valuable tool for the prognosis and diagnosis of cancer, however it requires a tradeoff between temporal and spatial resolution. The ultimate goal of this dissertation is to compare the temporal performance of three methods (spiral, propeller and variable density spiral), given a certain spatial resolution requirement, for the DCE-MRI. These methods show distinction from the conventional MRI methods in their k-space coverage. Propeller and Variable Density Spiral methods use an approach of oversampling the center of k-space, updating the central 13–20% of the radial k-space more frequently than the peripheries. The reason for this is that most of the image data resides in the central part of k-space. Spiral method, on the other hand approaches the problem by updating the overall k-space as fast as possible, faster than the conventional methods.; Comparison is performed mainly by computer simulations, where ground truth is known. In addition to computer simulations, these three methods are compared in-vivo, by tracking the DCE-MRI signal amplitude variation with time for each method on a healthy volunteer's liver.; One limitation of the spiral and variable density spiral imaging methods is the effect of off-resonance frequencies on image quality. For these spiral based methods, long readout times are desired to have short overall imaging times and high temporal resolution. However, for long readout times, off resonance frequencies blur the images and reduce the spatial resolution. In this dissertation a new method is proposed which is less complicated than most other methods, and reaches an acceptable level of accuracy with less amount of CPU time compared to previously effective methods.