PROPELLER-MRI: Data acquisition, motion correction and image reconstruction

PROPELLER is a novel MRI data acquisition and reconstruction technique and has reduced sensitivity to various sources of image artifacts. Data acquisition in PROPELLER is based on multiple-shot fast spin-echo, in which several k-space lines are acquired in each TR, forming a blade centered at the origin of k-space. The blade is then rotated around its center between shots, resulting in a k-space sampling pattern that resembles a propeller. The central disc of k-space is sampled by all blades and can be used as a 2D navigator. Comparison of this k-space disc between blades allows correction of the subject's in-plane rotation and translation, as well as identification of blades with corrupted data and exclusion of such blades from the final reconstruction. Furthermore, any residual errors are expressed in a benign fashion due to the radial nature of the acquisition. Therefore, PROPELLER-MRI is less sensitive to bulk motion than conventional FSE. However, data acquisition in PROPELLER is 50% longer than that of conventional FSE. Thus, one of the goals of this study was to investigate the effects of various PROPELLER acquisition parameters on motion correction and identify clinically appropriate acquisition strategies that minimize motion-related artifacts. Also the effects of under-sampling on PROPELLER images were evaluated using simulated and in vivo data sets, to reduce imaging time. It is well known that iterative reconstruction techniques mitigate artifacts arising from Nyquist holes in under-sampled k-space. In this work, a regularized iterative image reconstruction algorithm using NUFFT was applied to reconstruct images from PROPELLER-MRI acquisition in which, each blade is under-sampled in the phase-encoding direction. Image quality for various levels of under-sampling was investigated. The SNR was compared between images from under-sampled acquisitions and sufficiently sampled acquisitions with same imaging time. An accuracy of motion correction was investigated for various levels of under-sampling in PROPELLER acquisition.