Project Summary: The goal of the proposed project is to develop and validate a novel motion correction technique for 2D T2-weighted structural MRI of the brain. Head motion continues to be a substantial problem in the clinical setting, especially in patients who are confused or agitated, and in children and infants. A range of methods have been developed to attenuate motion artifacts for structural brain MRI from patients who move. These include prospective motion correction (PMC) using navigators for 3D acquisitions, as well as a special k- space trajectory (PROPELLER) that allows correction of in-plane motions during reconstruction of 2D scans. However, an entire class of motion artifacts in 2D structural MRI scans, including those from T2-weighted (T2W) scans, is not addressed by current motion correction techniques: those caused by Slice Alignment Errors (SAEs). These SAEs are caused by uncorrected through-plane movements and can occur both across and within excitations. We will develop a novel navigator that uses the spin history in slice direction as a “spin tag” to obtain fast estimates of the 3 through-plane velocities (1 translational and 2 rotational), which will then be used to realign slice objects in real-time (across and within excitations). The new navigator will be implemented with a standard RARE (or TSE) as well as a PROPELLER sequence. Optimized techniques will be validated in healthy subjects, using quantitative quality metrics. We hypothesize that elimination of SAEs “at the source” will significantly improve the quality of 2D T2W scans. Our Specific Aims are as follows. Aim 1: Develop a fast MR-based through-plane (“slice velocity”) navigator using spin-history profiles. Aim 1A: Develop and optimize the navigator to measure through-plane translational velocity (vz). Aim 1B: Develop and optimize the navigator to measure through-plane rotational velocities (ωx and ωy). Rationale: in first order, these 3 through-plane velocities fully determine SAEs and are the basis for Aim 2. Aim 2: Use through-plane velocities to correct SAEs in real-time in 2D RARE and PROPELLER scans. Aim 2A: Eliminate spin history effects across excitations and TR periods for RARE (e.g., TSE/FSE) scans. Aim 2B: Eliminate slice alignment errors (SAEs) within each RARE echo train. Aim 2C: Combine correction of through-plane motions with in-plane motion correction of PROPELLER. Rationale: the through-plane velocities from Aim 1 predict temporal changes in slice positions (in first order). PROPELLER provides in-plane motion correction but can fail when through-plane movements occur. Aim 3: Validate optimized motion-robust MRI methods in 10 healthy participants using trained motions. Hypothesis: in trained subjects who move intentionally, visual and quantitative quality metrics of T2W scans with motion correction ON will demonstrate better image quality than scans with motion correction OFF. Future work will add our navigator approach to FLAIR, DWI a...