Designing k-Space Filters to Improve Spatiotemporal Resolution with Sector-Wise Golden Angle (SWIG)

Abstract: The aim of this thesis is to design and evaluate k-space weighting filters for simultaneously improving the spatial and temporal resolution of cardiovascular MRI, with the ultimate goal of improving the accuracy of quantitative flow measurements, which are important for diagnosis and follow-up of heart dysfunction. Two different k-space filters were implemented and evaluated retrospectively to already acquired data. In addition, evaluation was performed with respect to tapering of the filters in the radial k-space direction, as well as accelerated imaging using undersampling. To better utilize the properties of the golden-angle acquisition, a k-space filter was also implemented where the temporal footprint increased in discrete steps, referred to as rings. The temporal footprint of each ring was calculated according to the Fibonacci sequence, and the starting position for each ring was computed to satisfy the Nyquist criterion. The k-space filters were evaluated in comparison to non-filtered reconstructions of cine and phase-contrast images. Motion-mode images were created from the cine images and used to evaluate the edge sharpness of the septal wall indicating the spatial resolution of the image. Phase-contrast images were used to measure peak flow velocity over the mitral valve, and the myocardial velocity in the early and late filling phases. The resolution of the peak is highly dependent on the temporal resolution. Measuring the peak velocity gave an indication of the temporal resolution, which could be compared to non-filter reconstructions. This study showed that k-space filters adapted to the Nyquist criterion improve the temporal resolution of peak velocity measures. Further investigation is justified to conclude if the performance exceeded the best performing method without k-space filters. However, the k-space filter showed substantial agreement with the best performing temporal footprint without k-space filter.