Off-resonance correction for magnetic resonance imaging with spiral trajectories

Abstract: The procedure of cardiographic magnetic resonance imaging requires patients to hold their breath for up to twenty seconds, creating an uncomfortable situation for many patients. It is proposed that an acquisition scheme using spiral trajectories is preferable due to their much shorter total scan time; however, spiral trajectories suffer from a blurring effect caused by off-resonance frequencies in the image area. There are several methods for reconstructing images with reduced blur and Conjugate Phase Reconstruction has been chosen as a method for implementation into Matlab-script for evaluation in regards to image reconstruction quality and computation time. This method finds a conjugate to the off-resonance from a field map to demodulate the image and an algorithm for frequency‑segmented Conjugate Phase Reconstruction is implemented along with an improvement called Multi-frequency Interpolation. The implementation is tested through simulation of spiral magnetic resonance imaging using a Shepp‑Logan phantom. Different off-resonance frequencies and field maps are used to provide a broad view of the functionality of the code. The two algorithms are then compared to each other in terms of computation speed and image quality. It is concluded that this implementation might reconstruct images well but that further testing on actual scan sequences is required to determine the usefulness. The Multi-frequency Interpolation algorithm yields images that are not useful in a clinical context. Further study of other methods not requiring a field map is suggested for comparison.