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An accurate planar visualization (curved planar reformation - CPR) of intracranial arteries is mandatory for an improved luminal and mural assessment especially in low resolution Magnetic Resonance Imaging (MRI) data sets acquired in standard clinical settings. CPR visualization methods based on the centerline of the desired structure are fast and easy to implement but the accuracy strongly depends on the spatial resolution of the 3D data set and the size of the desired vessel. In the manuscript, a novel algorithm for fast and robust centerline calculation in multi-contrast 3D MRI data is presented. It considers the extracted surface of the vessel structure for a more accurate centerline prediction resulting in an enhanced CPR visualization of small vessels., Comment: 7 pages, 10 figures

Purpose: To develop, optimize and implement a single shot spiral TSE-sequence at 3 T and to demonstrate its feasibility to acquire artefact free images of the central nervous system with 1 mm spatial resolution in < 200 ms. Theory and Methods: Spiral TSE sequences with annulated spiral segmentation have been implemented with different acquisition modes. In fixed mode the duration of each spiral segment is fixed to fill the available acquisition time tacq. In tangential mode, the beginning of each spiral segment is reached via a straight tangential trajectory. Tangential mode allows faster transition and thus longer tacq for a given echo spacing ESP, but less data points can be acquired per acquisition interval. Alternating between spiral-in and spiral-out readout in alternating echoes leads to a somewhat different point spread function for off-resonant spins. Results: Images of the brain with 1 mm spatial resolution acquired with a variable density spiral with ~45 % undersampling can be acquired in a single shot. All acquisition modes produce comparable image quality. Only mild artifacts in regions of strong susceptibility effects can be observed for ESP of 10 ms and below. The use of variable flip angle schemes allows seamless acquisition of consecutive slices and/or dynamic scans without waiting time between consecutive acquisitions. Comparison with images acquired at 1.5 T shows reduced susceptibility artifacts within the brain and facial structures.. Conclusion: Single shot spiral TSE has been demonstrated to enable highly efficient acquisition of high-resolution images of the brain in < 200 ms per slice., Comment: 16 pages, 10 figures, 5 supplementary figures, 1 supplementary table manuscript has been submitted to Magnetic Resonance in Medicine

We describe a new method for pulsed spin order transfer (SOT) of parahydrogen induced polarization (PHIP) that enables close to 100 % polarization in incompletely 2H-labeled molecules by exciting only the desired protons in a frequency-selective manner. While a selective pulse (SP) on 1H at the beginning of pulsed SOT had been considered before, using SPs during the SOT suppresses undesired indirect spin-spin interactions. As a result, we achieved a more robust SOT for the SP variants of the phINEPT+ sequence that we refer to as phSPINEPT+. Thereby, for the first time, we report a sequence that is effective for all weakly coupled spin systems. Our simulations show that the method converts close to 100 % of the parahydrogen-derived spin order into 13C hyperpolarization in weakly coupled three-spin systems and partially or fully 2H-labeled molecules if relaxation is neglected. Experimentally we demonstrate high hyperpolarization of 13C with 15.8 % for 1-13C-hydroxyethyl propionate-d3 and 12.6 % for 1-13C-ethyl acetate-d6, which corresponds to ~47 % and ~38 % if the enrichment of parahydrogen had been 100 %. Even in non-2H-labeled molecules, a remarkable 13C polarization is achieved, e.g. up to 20 % were simulated for 100 % pH2, and 1.25 % were obtained experimentally for 1-13C-ethyl pyruvate and 50 % pH2, which can be further improved by faster hydrogenation. As a result, full deuterium labeling may no longer be required e.g., when new PHIP agents are investigated, the synthesis of fully deuterated molecules is too complex, or when a kinetic isotope effect regarding the metabolic conversion rate of an agent is to be avoided. Using SPs during SOT seems very promising and may be extended to other sequences in the context of PHIP and be-yond to make them less prone to experimental imperfections or real molecular environments., Comment: 7 pages, 3 figures and supporting materials

Wall shear stress (WSS) has been suggested as a potential biomarker in various cardiovascular diseases and it can be estimated from phase-contrast Magnetic Resonance Imaging (PC-MRI) velocity measurements. We present a new parametric sequential method for MRI-based WSS quantification consisting of a geometry identification and a subsequent approximation of the velocity field. The new method was validated on well controlled, high resolution in vitro measurements of turbulent stationary flows and physiological pulsatile flows in phantoms. Basic applicability to in vivo was demonstrated using 2D PC-MRI data of the ascending aorta of three volunteers.

Purpose The proposed reconstruction framework addresses the reconstruction accuracy, noise propagation and computation time for Magnetic Resonance Fingerprinting (MRF). Methods Based on a singular value decomposition (SVD) of the signal evolution, MRF is formulated as a low rank inverse problem in which one image is reconstructed for each singular value under consideration. This low rank approximation of the signal evolution reduces the computational burden by reducing the number of Fourier transformations. Also, the low rank approximation improves the conditioning of the problem, which is further improved by extending the low rank inverse problem to an augmented Lagrangian that is solved by the alternating direction method of multipliers (ADMM). The root mean square error and the noise propagation are analyzed in simulations. For verification, in vivo examples are provided. Results The proposed low rank ADMM approach shows a reduced root mean square error compared to the original fingerprinting reconstruction, to a low rank approximation alone and to an ADMM approach without a low rank approximation. Incorporating sensitivity encoding allows for further artifact reduction. Conclusion The proposed reconstruction provides robust convergence, reduced computational burden and improved image quality compared to other MRF reconstruction approaches evaluated in this study., Comment: 47 Pages, 11 Figures, 1 Table