Development of new phase-encoding schemes for magnetization-prepared fast MR imaging

Abstract

For magnetization-prepared imaging (i.e., diffusion, perfusion, magnetization transfer, inversion recovery imaging) which requires a specific magnetization preparation before the actual data acquisition, a centric phase encoding reordering where the center of the k-space is acquired first is preferred to the linear PE order in order to maximize SNR of the prepared signal. However, especially in fast MR imaging sequences, the conventional centric ordering scheme either induces severe artifacts or has limited usage due to its alternating polarity and amplitude of the phase encoding gradients. There have been several studies to overcome the limitations of the conventional centric ordering method, but suggested techniques were not optimized for magnetization-prepared imaging. This dissertation focuses on the development of new data acquisition ordering methods which are beneficial for various magnetization-prepared imaging techniques with two representative fast MR sequences, balanced steady-state free precession (bSSFP) and echo planar imaging (EPI). First, phase encoding grouping and four average schemes were proposed to reduce eddy-current artifacts and transient oscillations while maximizing the SNR of the magnetization-prepared imaging in bSSFP readout. Second, single-shot pseudo-centric EPI was proposed for improving the SNR of magnetization-prepared imaging by reducing the echo time significantly without distinct geometric distortion and image artifacts. The results showed the potential advantages of proposed methods over the conventional techniques.