Self-navigated motion correction using moments of spatial projections in radial MRI

Abstract

Interest in radial MRI, also known as projection reconstruction (PR) MRI, has increased recently for uses such as fast scanning and undersampled acquisitions. Additionally, PR acquisitions have intrinsic advantages over standard two-dimensional Fourier transform (2DFT) imaging with respect to motion of the imaged object. It is well known that alignment of each spatial domain projection's center of mass (calculated using each projection's 0th and 1st moments) to the center of the field of view corrects shifts caused by in-plane translation. Here we report a previously unrealized ability to determine the in-plane rotational motion of an imaged object using the 2nd moments of the translation-corrected spatial domain projections. The correction requires only the PR data itself and a new projection view angle acquisition time order. The proposed view angle time order allows the acquisition to be "self-navigating" with respect to both in-plane translation and rotation. Image reconstruction using the aligned projections and detected acquisition angles can eliminate or significantly reduce image artifacts due to such motion. We describe the theory of the correction technique and demonstrate its effectiveness using a computer-controlled motion phantom executing 2-D in-plane translations and a customized pulse sequence capable of introducing known in-plane rotational errors.