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Purpose: To enable fast and flexible high-resolution four-dimensional (4D) MRI of periodic thoracic/abdominal motion for motion visualization or motion-corrected imaging., Methods: We proposed a Cartesian three-dimensional k-space sampling scheme that acquires a random combination of k-space lines in the ky/kz plane. A partial Fourier-like constraint compacts the sampling space to one half of k-space. The central k-space line is periodically acquired to allow an extraction of a self-navigated respiration signal used to populate a k-space of multiple breathing positions. The randomness of the acquisition (induced by periodic breathing pattern) yields a subsampled k-space that is reconstructed using compressed sensing. Local image evaluations (coefficient of variation and slope steepness through organs) reveal information about motion resolvability. Image quality is inspected by a blinded reading. Sequence and reconstruction method are made publicly available., Results: The method is able to capture and reconstruct 4D images with high image quality and motion resolution within a short scan time of less than 2 min. These findings are supported by restricted-isometry-property analysis, local image evaluation, and blinded reading., Conclusion: The proposed method provides a clinical feasible setup to capture periodic respiratory motion with a fast acquisition protocol and can be extended by further surrogate signals to capture additional periodic motions. Retrospective parametrization allows for flexible tuning toward the targeted applications. Magn Reson Med 78:632-644, 2017. © 2016 International Society for Magnetic Resonance in Medicine., (© 2016 International Society for Magnetic Resonance in Medicine.)

Purpose: To design a phantom for diffusion-weighted imaging (DWI) with defined apparent diffusion coefficients (ADC) and T2 relaxation times., Methods: Varying concentrations of polyethylene glycol (PEG) were used for the adjustment of diffusivity. T2 relaxation times were tuned by adding of the MR contrast agent gadobutrol. Relaxation times and apparent diffusion coefficients were quantified using a multiecho spin echo sequence and an echo planar imaging (EPI) DWI sequence, respectively, on a 3T clinical scanner., Results: Increasing concentrations of PEG led to a marked impairment of diffusivity accompanied by only moderate changes of T2 relaxation times. Adding gadobutrol to the PEG solutions allowed for adjustment of transverse relaxation times to predefined values. Thus, a broad range of defined ADC values and T2 relaxation times could be accurately achieved in the final phantom., Conclusion: The proposed phantom allows for standardized in vitro studies of DWI methods and protocols. The obtained MR image contrasts are similar to a variety of biological tissues, which can contribute to optimization of imaging techniques with respect to specific clinical questions. Due to the simplicity of design and the accessibility of the contained compounds, this phantom may also serve as a tool for standardization and calibration., (Copyright © 2013 Wiley Periodicals, Inc.)

Purpose: To improve the visualization of fibrous tissues as tendons, ligaments and fibrocartilage structures as menisci by positive contrast using a new 3D Double Echo Steady State (DESS) sequence., Methods: The proposed 3D DESS sequence works with separate acquisition of a first echo with an echo time (TE1 ) of 1.2 ms followed by a more heavily T2 -weighted second echo recorded at time TE2 . Subtraction of images from both echoes leads to positive signal from fibrous tissues, whereas in other tissues as musculature and fat the subtraction signal nearly vanishes due to almost similar signal strength in both echoes. Systematic measurements in healthy volunteers with different sets of pulse repetition time (TR), TE1 , readout bandwidth and flip angle were performed to determine optimal sequence parameters., Results: The presented 3D sequence with Cartesian readout requires relatively short measuring time, provides reasonable signal-to-noise ratio and can be easily implemented in protocols for clinical musculoskeletal MR imaging. Degenerative changes or tears of tendons, ligaments and fibrocartilage are known to cause increased water content and therefore prolongation of transverse relaxation times, which leads to reduced signal intensities in the "subtraction images.", Conclusion: Positive contrast of fibrous tissue as demonstrated by the proposed sub-DESS approach provides improved conspicuity and allows for three-dimensional reconstruction especially of structures with curved geometry., (Copyright © 2013 Wiley Periodicals, Inc.)

Magnetization transfer (MT) contrast imaging reveals interactions between free water molecules and macromolecules in a variety of tissues. The introduction of ultrashort echo time (UTE) sequences to clinical whole-body MR scanners expands the possibility of MT imaging to tissues with extremely fast signal decay such as cortical bone. The aim of this study was to investigate the MT effect of bovine cortical bone in vitro on a 3 Tesla whole-body MR unit. A 3D-UTE sequence with a rectangular-shaped on-resonant excitation pulse and a Gaussian-shaped off-resonant saturation pulse for MT preparation was applied. The flip angle and off-resonance frequency of the MT pulse was systematically varied. Measurements on various samples of bovine cortical bone, agar gel, aqueous manganese chloride solutions, and solid polymeric materials (polyurethane) were performed, followed by preliminary applications on human tibial bone in vivo. Direct on-resonant saturation effects of the MT prepulses were calculated numerically by means of Bloch's equations. Corrected for direct saturation effects dry and fresh bovine cortical bone showed "true" MTR values of 0.26 and 0.21, respectively. In vivo data were obtained from three healthy subjects and showed MTR values of 0.30 +/- 0.08. In vivo studies into MT of cortical bone might have the potential to give new insights in musculoskeletal pathologies., ((c) 2009 Wiley-Liss, Inc.)