JVC-GRAPPA takes advantage of additional spatial encoding from phase information and image similarity, and employs different sampling patterns across acquisitions. J-LORAKS achieves a more parsimonious low-rank representation of local k-space by considering multiple images as additional coils. Both approaches provide dramatic improvement in artifact and noise mitigation over conventional single-contrast parallel imaging reconstruction. Magn Reson Med 80:619-632, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Purpose Whole-brain high-resolution quantitative imaging is extremely encoding intensive, and its rapid and robust acquisition remains a challenge. Here we present a 3D MR fingerprinting (MRF) acquisition with a hybrid sliding-window (SW) and GRAPPA reconstruction strategy to obtain high-resolution T1, T2 and proton density (PD) maps with whole brain coverage in a clinically feasible timeframe. Methods 3D MRF data were acquired using a highly under-sampled stack-of-spirals trajectory with a steady-state precession (FISP) sequence. For data reconstruction, kx-ky under-sampling was mitigated using SW combination along the temporal axis. Non-uniform fast Fourier transform (NUFFT) was then applied to create Cartesian k-space data that are fully-sampled in the in-plane direction, and Cartesian GRAPPA was performed to resolve kz under-sampling to create an alias-free SW dataset. T1, T2 and PD maps were then obtained using dictionary matching. Results Phantom study demonstrated that the proposed 3D-MRF acquisition/reconstruction method is able to produce quantitative maps that are consistent with conventional quantification techniques. Retrospectively under-sampled in vivo acquisition revealed that SW + GRAPPA substantially improves quantification accuracy over the current state-of-the-art accelerated 3D MRF. Prospectively under-sampled in vivo study showed that whole brain T1, T2 and PD maps with 1 mm3 resolution could be obtained in 7.5 min. Conclusions 3D MRF stack-of-spirals acquisition with hybrid SW + GRAPPA reconstruction may provide a feasible approach for rapid, high-resolution quantitative whole-brain imaging.

Purpose To implement and validate a previously proposed ultra-short echo time (UTE) method for measuring collagen-bound and pore water concentrations in bone based on their T2 differences. Methods Clinically compatible UTE image sequences for quantitative T2-based bound and pore water imaging in bone were implemented and validated on a 3T human scanner and a 4.7T small bore system. Bound and pore water images were generating using T2-selective adiabatic pulses. In both cases, the magnetization preparation was integrated into a 3D UTE acquisition, with 16 radial spokes acquired per preparation. Images were acquired from human cadaveric femoral mid-shafts, from which isolated bone samples were subsequently extracted for non-imaging analysis using T2 spectroscopic measurements. Results A strong correlation was found between imaging-derived concentrations of bound and pore water and those determined from the isolated bone samples. Conclusion These studies demonstrate the translation of previously developed approaches for distinguishing bound and pore water from human cortical bone using practical human MRI constraints of gradient performance and RF power deposition.

).q RSNA, 2015 Purpose:To translate and evaluate an in vivo magnetic resonance (MR) imaging protocol for quantitative mapping of collagen-bound and pore water concentrations in cortical bone that involves relaxation-selective ultrashort echo time (UTE) methods. Materials and Methods:All HIPAA-compliant studies were performed with institutional review board approval and written informed consent. UTE imaging sequences were implemented on a clinical 3.0-T MR imaging unit and were used for in vivo imaging of bound and pore water in cortical bone. Images of the lower leg and wrist were acquired in five volunteers each (lower leg: two men and three women aged 24, 24, 49, 30, and 26 years; wrist: two men and three women aged 31, 23, 25, 24, and 26 years) to generate bound and pore water concentration maps of the tibia and radius. Each volunteer was imaged three times, and the standard error of the measurements at the region-of-interest (ROI) level was computed as the standard deviation across studies, pooled across volunteers and ROIs. Results:Quantitative bound and pore water maps in the tibia and radius, acquired in 8-14 minutes, had per-voxel signal-tonoise ratios of 18 (bound water) and 14 (pore water) and inter-study standard errors of approximately 2 mol 1 H per liter of bone at the ROI level. Conclusion:The results of this study demonstrate the feasibility of quantitatively mapping bound and pore water in vivo in human cortical bone with practical human MR imaging constraints.q RSNA, 2015