Development and Applications of 3D Ultra-short Echo Time MRI with Rosette k-Space Pattern
Magnetic resonance imaging (MRI) plays an important role in providing structural information, aiding in disease diagnosis, probing neuron activities, and etc. Sampling k-space, which is the Fourier transform of the image, is a necessary step in MRI scans. The most widely used k-space sampling strategy is the Cartesian trajectories. However, novel non-Cartesian trajectories are flexible and efficient in k-space sampling, permit shorter echo time, and are insensitive to motion artifacts. The non-Cartesian k-space patterns include radial, spiral, concentric rings, rosette, and etc. Some protons restricted by the chemical environment, or other nuclei because of their nature, have short transverse relaxation times (T2). Ultra-short echo time (UTE) and zero echo time (ZTE) modalities are the promising techniques to capture the rapid decaying signals directly. The common k-space pattern for UTE and ZTE applications is the three-dimensional radial acquisition, which allows a center-out trajectory. Rosette k-space trajectory, which also allows center-out sampling, is a potential candidate for UTE purposes. In addition, it acquires more samples in the peripheral k-space for better spatial resolution, and is more incoherent to stand image quality upon undersampling than radial. However, the rosette trajectories have not yet been applied in UTE.
In this study, a 3D rosette k-space trajectory designed for UTE acquisition is developed. In addition, a rosette-based magnetic resonance spectroscopic imaging (MRSI) is also developed to measure metabolites with short echo time. A comparison between 3D rosette and 3D radial UTE sequences, based on both phantom and in vivo scans, was performed to test the performance of the novel sequence. In addition, the 3D rosette UTE sequence was also applied in 1) myelin bilayer imaging, 2) brain iron content mapping, 3) cartilage image by sodium MRI, and 4) phosphorus MRSI. In summary, the 3D rosette k-space trajectory performs better than radial, in terms of point spread function (PSF), signal-to-noise ratio (SNR), and ability to provide structural details. Furthermore, the applications have demonstrated that 3D rosette UTE sequence is able to capture fast decaying signals.
- Doctor of Philosophy
- Biomedical Engineering
- West Lafayette