Yuhang Shi¹, Johanna Vannesjo¹, Karla Miller¹, and Stuart Clare^1
1Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, Oxford, United Kingdom

Slice-wise dynamic shimming is used in ultra-high-field MRI research due to its capability to produce a more homogeneous field than static shimming. This work presents a field-map-free approach to first-order dynamic shimming, which can reduce the time spent on shim determination compared with field-map-based approaches, whilst still outperforming static shimming.

Anna Andreychenko¹, Baudouin Denis de Senneville^1,2, Robin J.M. Navest¹, Jan J.W. Lagendijk¹, and Cornelis A.T. van den Berg^1
1Imaging Division, UMC Utrecht, Utrecht, Utrecht, Netherlands, ²IMB, UMR 5251 CNRS/University of Bordeaux, Bordeaux, France

Motion detection and correction are always required for successful human abdominal and thoracic MR imaging and are essential for MR guided treatments of mobile organs. Here we propose an MR-based 2D motion model which uses a noise covariance matrix dynamics as a surrogate signal. Since the noise covariance matrix of the array senses the volumetric motion and can be updated very fast (i.e. every k-line), the proposed model does not lead to the spatial/temporal tradeoffs in contrary to the models which are updated by MR navigators.

Kelvin Layton¹, Stefan Kroboth¹, Feng Jia¹, Sebastian Littin¹, Huijun Yu¹, and Maxim Zaitsev^1
1Medical Physics, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany

Spatial encoding magnetic fields (SEMs) that vary nonlinearly over the field-of-view offer potential advantages for image encoding. This work investigates intra-voxel dephasing in the imaging plane when nonlinear SEMs are used. Intra-voxel dephasing reduces the signal from a voxel for strong encoding moments depending on the location of the pixel and the nonlinear fields used. A new signal model explicitly accounting for intra-voxel dephasing is derived to accurately explain experimental data acquired with nonlinear SEMs. Images reconstructed using the new signal model exhibit substantially less noise and fewer artifacts compared to the traditional signal encoding model.

Jun Shen^1
1NIMH, Bethesda, MD, United States

A new imaging technique is described which essentially stretches a predetermined region of interest in the object to be imaged by interacting linear magnetic field gradients with a series of radiofrequency magnifying pulses. These magnifying pulses progressively bend the phase of electromagnetic signals from the imaging focus during phase encoding. As a result, the differential phase evolution at the imaging focus is faster than in conventional MRI, leading to focal resolution enhancement. This technique is demonstrated by phantom and in vivo imaging.

Pei-Hsin Wu¹, Hsiao-Wen Chung¹, and Nan-Kuei Chen^2
1Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, ²Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States

MRI phase mapping is difficult because of the phase wrap-around. Although phase unwrapping procedures have been implemented, their performance may degrade significantly when being applied to phase images of low SNR. To address this challenge, we 1) report a novel procedure for mapping phase gradients of low-SNR images through quantifying the k-space energy peak displacement, and 2) develop a robust phase unwrapping method that incorporates phase gradient information derived from the k-space analysis. Our preliminary results indicate that the developed methods can reliably measure the phase gradient values and successfully achieve phase unwrapping for images with low SNR.

Barbara Cervantes¹, Jinnan Wang², Jan S. Bauer³, Hendrik Kooijman⁴, Peter Börnert⁵, Axel Haase⁶, Ernst J. Rummeny¹, Klaus Wörtler¹, and Dimitrios C. Karampinos^1
1Diagnostic and Interventional Radiology, Technische Universität München, Munich, Germany, ²Philips Research North America, Seattle, WA, United States, ³Neuroradiology, Technische Universität München, Munich, Germany, ⁴Philips Healthcare, Hamburg, Germany, ⁵Philips Research Laboratory, Hamburg, Germany, ⁶Zentralinstitut für Medizintechnik, Technische Universität München, Garching, Germany

A general problem in peripheral nerve imaging is the presence of vessels in close proximity to the nerves. Motion-sensitized driven equilibrium (MSDE) preparation and low b-value diffusion weighting have been previously proposed to suppress vessel signal when imaging peripheral nerves. However, blood signal suppression can be challenging in slowly flowing vessels. The present work aims to maximize the efficiency of vessel signal suppression by proposing an orthogonally combined motion- and diffusion- sensitized driven equilibrium (OC-MDSDE) preparation. OC-MDSDE is combined with a 3D TSE readout and preliminary results are shown in imaging the nerves of the lower leg.

Jessica A.M. Bastiaansen^1,2, Helene Feliciano^1,2, Andrew Coristine^1,2, and Matthias Stuber^1,2
1Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland, ²Center for Biomedical Imaging (CIBM), Lausanne, Switzerland

By exploiting the frequency dispersion of protons residing in the dipolar field of FeO constrast agents that are injected intravenously, positive contrast MRI is enabled. Here, off-resonance imaging was exploited to explore positive contrast generation by using extraneous paramagnetic biomarkers, specifically targeting the labeling of moving protons. Spin labeling was thus achieved in a flow phantom using off-resonant imaging. Different delay times of the saturation pulse lead to a more extensive range of labeled spins, and time resolved positive contrast imaging of downstream areas. It allows for flow visualization in the vicinity of paramagnetic objects without the need for contrast injection.

Stephen F Cauley^1,2, Kawin Setsompop^1,2, Dan Ma³, Yun Jiang³, Elfar Adalsteinsson⁴, Lawrence Wald^1,2, and Mark Griswold^3,5
1Athinoula A. Martinos Center for Biomedical Imaging, MGH/HST, Charlestown, MA, United States, ²Dept. of Radiology, Harvard Medical School, Boston, MA, United States, ³Dept. of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, ⁴Harvard-MIT Div. of Health Sci. and Tech., Dept. of Electrical Engineering and Computer Science, Cambridge, MA, United States, ⁵Dept. of Radiology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio, United States

Reconstruction of non-Cartesian data can be a computationally demanding problem. Iterative numerical solutions often involve repeated evaluation of Discrete Fourier or NUFT operators, coil sensitivity profiles, and other physical MR parameters. Alternatively, Hierarchically Semiseparable (HSS) modeling can be used to compute an approximate inverse of the generalized encoding matrix. The HSS model can be computed prior to data collection and is ideal for time series reconstruction, e.g. fMRI, cardiac imaging, and MR fingerprinting. We demonstrate a 40x speed-up when compared to state-of-the-art iterative solvers for the reconstruction of distortion corrected spiral data.

Anthony G. Christodoulou¹ and Zhi-Pei Liang^1
1Beckman Institute and Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States

This work describes a novel method for highly accelerated multiparameter mapping exploiting the low-rank tensor structure induced by partial separability of the desired multivariate image function. We demonstrate the proposed tensor-based data acquisition and reconstruction method for highly accelerated multiparameter mapping and demonstrate this method for accelerated FLASH-based , T₁, and T₂^* mapping of an ex vivo rat heart infiltrated by superparamagnetic iron oxide (SPIO)-labeled macrophages, which produced excellent reconstruction results from very sparsely sampled data.

Yun Jiang¹, Dan Ma¹, Himanshu Bhat², Huihui Ye^3,4, Stephen F. Cauley³, Lawrence L. Wald^3,5, Kawin Setsompop³, and Mark A. Griswold^1,6
1Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, ²Siemens Medical Solutions USA Inc., Charlestown, Massachusetts, United States, ³Department of Radiology, Massachusetts General Hospital, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, Massachusetts, United States, ⁴Department of Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China,⁵Department of Electrical Engineering and Computer Science; Harvard-MIT Division of Health Sciences a, MIT, Cambridge, Massachusetts, United States, ⁶Department of Radiology, Case Western Reserve University, Cleveland, Ohio, United States

By pseudo-randomly varying the acquisition parameters, the MRF framework pursues unique signal evolutions for different tissue types. Multiple parameters can be simultaneously quantified by a pattern-matching algorithm. In this study, we explored the possibility to extend this concept for further accelerating the MRF acquisition along the slice direction. By exciting two slices with different patterns of flip angles simultaneously, each slice could have its own distinguishable signal evolution. By matching the mixed signal from both slices to the pre-calculated dictionary of each slice, T1 and T2 values of each slice can be directly quantified, respectively.

Kevin M Koch¹, Ajeet Gaddipati², Ali Ersoz³, Robert Peters², Valentina Taviani⁴, Brian A Hargreaves⁴, and L. Tugan Muftuler^5
1Biophysics and Radiology, Medical College of Wisconsin, Milwaukee, WI, United States, ²GE Healthcare, Milwaukee, WI, United States, ³Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, ⁴Radiology, Stanford University, Stanford, CA, United States, ⁵Neurosurgery and Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States

Multi-spectral diffusion-weighted imaging near metal implants is presented. The presented approach merges non-CPMG PROPELLER diffusion-weighting imaging techniques with Multi-Spectral-Imaging methods for metal artifact reduction. A fundamental demonstration of multi-spectral non-CPMG diffusion-weighted PROPELLER spectral bin formation is presented. The presented methods are then applied in preliminary form to reduce metal susceptibility artifacts in diffusion-weighted imaging in phantoms at 3T.

Valentina Taviani¹, Suchandrima Banerjee², Bruce L. Daniel¹, Shreyas S. Vasanawala¹, and Brian A. Hargreaves^1
1Radiology, Stanford University, Stanford, CA, United States, ²Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

A novel multiband technique for high resolution diffusion weighted imaging is demonstrated in the breast of a healthy volunteer. The proposed method uses a phase-modulated 2D RF pulse that simultaneously excites multiple co-planar bands of magnetisation in conjunction with a refocusing pulse with multiband slice selectivity. Reduced FOV encoding (i.e. in-plane acceleration) and a generalised parallel imaging reconstruction technique based on the complementarity between coil sensitivities and excitation profiles are used to obtain high-resolution diffusion weighted images with limited distortion.

Ziying Yin¹, Steven Kearney², Richard L. Magin¹, and Dieter Klatt^1
11Richard and Loan Hill Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ²2Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, United States

Here we introduce a recipe for the simultaneous acquisition of Diffusion tensor imaging (DTI) and 3D-vector field MR Elastography (MRE) data. The simultaneous encoding of MRE and diffusion is first achieved by modulating the timing of the motion-sensitizing gradient with the diffusion time, and with the mechanical vibration frequency. The simultaneous acquisition of a 3D-vector field MRE and DTI is then achieved by designing a particular gradient encoding scheme with the application of a series of motion-sensitizing gradients in non-collinear and non-coplanar directions. The present work demonstrates the feasibility of the proposed concept in the mouse brain in vivo.

Daniel Brenner¹, Desmond H. Y. Tse^2,3, Patrick J. Ledden⁴, Claudine Neumann¹, and Tony Stöcker^1,5
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Faculty of Psychology, Maastricht University, Maastricht, Netherlands,³Department of Radiology, Maastricht University Medical Centre, Maastricht, Netherlands, ⁴Nova Medical, Inc., Wilmington, MA, United States,⁵Department of Physics and Astronomy, University of Bonn, Bonn, Germany

Fast transmit array mapping requires interferometric measurements for good conditioning of the B1 mapping problem. This work demonstrates the application of two distinct interferometry encoding schemes to the acquisition and preparation block of a 3D DREAM sequence, respectively. This allows efficient and precise generation of single channel coil maps – as confirmed by simulations – and retains the relative transmit phase.

Mohammad Mehdi Khalighi¹ and Peng Lai^1
1Applied Science Lab, GE Healthcare, Menlo Park, CA, United States