Jongyeon Lee¹, Byungjai Kim¹, Namho Jeong¹, and Hyunwook Park^1
1Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea

Numerous motion correction methods have been developed to reduce motion artifacts and improve image quality in MRI. Conventional techniques utilizing motion measurement required a prolonged scan time or intensive computational costs. Deep learning methods have opened up a new way for motion correction without motion information. A proposed method using a multi-input neural network with the structural similarity loss takes an advantage of a common clinical setting of multi-contrast acquisition to clearly correct motion artifacts in brain imaging. Motion artifacts can be fully retrospectively and greatly reduced without any motion measurement by the proposed method.

Nurten Ceren Askin Incebacak¹, Tess E. Wallace², Tobias Kober^3,4,5, Francois Lazeyras¹, Simon K. Warfield², and Onur Afacan^2
1Department of Radiology and CIBM, University of Geneva, Geneva, Switzerland, ²Department of Radiology, Boston Children's Hospital and Harvard Medical School, Boston, MA, United States, ³Advanced Clinical Imaging Technology, Siemens Healthcare, Lausanne, Switzerland, ⁴Department of Radiology, UNIL and CHUV, Laussanne, Switzerland, ⁵LTS5, EPFL, Lausanne, Switzerland

In this work, we propose to measure and correct rigid body head motion using slab-selective FID navigators. It is possible to estimate motion without relying on any patient specific choreographic training by using simulated motion data and a forward model of FIDnav signal generation by including slab profile estimation. This calibration procedure provides a more practical solution, particularly for pediatric applications where subjects are unable to cooperate with specific instructions. 

Onur Afacan¹, W. Scott Hoge², Tess E. Wallace¹, Tobias Kober^3,4,5, Daniel Nicolas Splitthoff⁶, Ali Gholipour¹, Sila Kurugol¹, Camilo J. Cobos¹, Richard L. Robertson¹, and Simon K. Warfield^1
1Department of Radiology, Boston Children's Hospital and Harvard Medical School, Boston, MA, United States, ²Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States, ³Advanced Clinical Imaging Technology, Siemens Healthcare, Lausanne, Switzerland, ⁴Department of Radiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ⁵École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, ⁶Siemens Healthcare, Erlangen, Germany

Large head motion induces different local magnetic-field inhomogeneities, even if the field of view is corrected prospectively. In this work, we implemented and evaluated a diffusion-weighted dual-echo EPI sequence that prospectively corrects for motion using real-time measurements from an optical tracker and uses echoes acquired with reversed phase-encoding to correct for the distortions resulting from the induced local magnetic field inhomogeneities. We evaluated our motion and distortion correction framework in volunteer experiments undergoing controlled motion, and in pediatric patients undergoing routine MRI. Prospective motion correction using our proposed method produced high-quality diffusion parameter maps in all volunteer and patient scans.

Tess E. Wallace^1,2, Onur Afacan^1,2, Tobias Kober^3,4,5, and Simon K. Warfield^1,2
1Computational Radiology Laboratory, Boston Children's Hospital, Boston, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Advanced Clinical Imaging Technology, Siemens Healthcare, Lausanne, Switzerland, ⁴Radiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ⁵LTS5, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

FIDnavs can be acquired extremely rapidly using standard scanner hardware and are consequently an attractive tracking strategy for prospective motion correction (PMC), which requires accurate pose updates to be passed to the sequence with minimal delay. In this work, we demonstrate for the first time the efficacy of PMC using FIDnav motion estimates in a moving phantom and in volunteers performing deliberate head motion. Real-time pose updates from measured FIDnavs enabled substantial improvements in image quality in structural scans acquired with motion. FID-navigated PMC is a promising method for motion-robust imaging of patients who have difficulty staying still during imaging. 

Kamlesh Pawar¹, Jarrel Seah², Meng Law³, Tom Close⁴, Zhaolin Chen¹, and Gary Egan^1
1Monash Biomedical Imaging, Monash University, Melbourne, Australia, ²Department of Neuroscience, Monash University, Melbourne, Australia, ³Radiology and Nuclear Medicine, Alfred Health, Melbourne, Australia, ⁴Monash Biomedical Imging, Monash University, Melbourne, Australia

The deep learning techniques have been shown to reduce the motion artifact in simulated motion scenarios and a few volunteer scans, the validation of it during routine clinical scans remains an unanswered question. In this study, we focus on evaluating the quality of images from the DL motion correction approach on a cohort of 27 actual patient motion cases that were obtained from the routine clinical scans. Two board-certified radiologists evaluated 9 anatomical regions in the 3D MPRAGE brain images and rated them on the 3-point scale.  

Lucas Soustelle^1,2, Julien Lamy³, Arnaud Le Troter^1,2, Patrick Viout^1,2, Lauriane Pini^1,2, Claire Costes^1,2, Jean-Philippe Ranjeva^1,2, Maxime Guye^1,2, Adil Maarouf^1,2,4, Bertrand Audoin^1,2,4, Clémence Boutière^1,2,4, Audrey Rico^1,2,4, Gopal Varma⁵, David C Alsop⁵, Jean Pelletier^1,2,4, Olivier M Girard^1,2, and Guillaume Duhamel^1,2
1Aix-Marseille Univ, CNRS, CRMBM, Marseille, France, ²APHM, Hôpital Universitaire Timone, CEMEREM, Marseille, France, ³Université de Strasbourg, CNRS, ICube, FMTS, Strasbourg, France, ⁴APHM, Hôpital Universitaire Timone, Service de neurologie, Marseille, France, ⁵Division of MR Research, Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States

Multi-contrast-based parametric MRI techniques provide parametric maps intrinsically sensitive to voxel misalignment upon images combination.

In this work, we propose an efficient retrospective motion correction method adapted to this problem, with an application to inhomogeneous Magnetization Transfer (ihMT) imaging. The proposed method is confronted with the MCFLIRT (FSL) method used as reference, and residual motion is quantified and analysed across native and motion corrected images.

Tobias Hepp¹, Karim Armanious^1,2, Aastha Tanwar², Sherif Abdulatif², Thomas Küstner¹, Bin Yang², and Sergios Gatidis^1
1University Hospital Tübingen, Tübingen, Germany, ²University of Stuttgart, Stuttgart, Germany

Motion is one of the main sources for artifacts in magnetic resonance (MR) imaging and can affect the diagnostic quality of MR images significantly. Previously, supervised adversarial approaches have been suggested for the correction of MR motion artifacts. However,supervised approaches require paired and co-registered datasets for training, which are often hard or impossible to acquire. We introduced a new adversarial framework for the unsupervised correction of severe rigid motion artifacts in the brain region. Quantitative and qualitative comparisons with other supervised and unsupervised translation approaches showed the enhanced performance of the introduced framework.

Nadine N Graedel¹, Yael Balbastre¹, Nadège Corbin¹, Oliver Josephs¹, and Martina F Callaghan^1
1Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom

The increased SNR offered by 3D EPI makes it well-suited for high-resolution fMRI but this benefit needs to be weighed against the increased motion sensitivity. Even when prospective motion correction is used to create a consistent excitation volume and image encoding, residual artefacts remain, caused for example by the apparent motion of coil sensitivities relative to the head after PMC. Using simulated fMRI data we examined the impact of this effect on fMRI and a potential correction using motion-adjusted GRAPPA calibration combined with volume-wise bias field removal which in simulations achieved improved sensitivity and specificity of detection of activation.

Pedro Lima Cardoso¹, Gregor Körzdörfer², Eva Hečková¹, Mathias Nittka², Siegfried Trattnig^1,3, and Wolfgang Bogner^1,3
1High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria, ²Siemens Healthcare GmbH, Erlangen, Germany, ³Christian Doppler Laboratory for Clinical Molecular MR Imaging, MOLIMA, Vienna, Austria

Motion-induced artifacts in quantitative MRI may not be visually detectable. MRF has shown to be robust to in-plane movement, and methods to mitigate it were made available. However, the impact of clinically prevalent motion patterns has not yet been investigated. The effect of realistic motion data from patients with neurodegenerative disorders and young/elderly controls on 2D FISP-MRF is therefore investigated in this simulation study. Results are validated with in-vivo motion-tracked measurements. Although through-plane motions were shown to significantly impact MRF parametric maps (particularly T2), MRF may preserve its sensitivity in clinical cases in which expected lesion-related differences are large enough.

Laura Bortolotti¹ and Richard Bowtell^1
1Physics, Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom

A fixed array of NMR field probes has proved to be a valid tool for monitoring the effects of a wide range of head movements in a 7T scanner. Here, we use this set up to detect significant field changes in order to give early feedback on head motion. This information could be used in deciding to stop a scan or to reacquire all or part of the k-space data in order to avoid acquisition of motion corrupted image data. This method can be implemented without requiring image sequence modification nor rigid coupling of a motion marker to the head.

Isabelle Heukensfeldt Jansen¹, Sangtae Ahn¹, Rafi Brada², Michael Rotman², and Christopher J. Hardy^1
1GE Global Research Center, Niskayuna, NY, United States, ²GE Global Research Center, Herzliya, Israel

We introduce ISHMAPS, a method for detecting and adapting to patient motion in real time during an MR scan. The method uses a neural network trained on motion-corrupted data to detect and score motion using as little as 6% of k-space. Once motion is detected, multiple separate complex sub-images from different motion states can be reconstructed and combined into a motion-free image, or the scan can adaptively re-acquire sections of k-space taken before motion occurred.

Phillip DiGiacomo¹, Mackenzie Carlson¹, Julian Maclaren¹, Murat Aksoy¹, Yi Wang², Pascal Spincemaille², Brian Burns³, Roland Bammer¹, Brian Rutt¹, and Michael Zeineh^1
1Stanford University, Stanford, CA, United States, ²Cornell University, Ithaca, NY, United States, ³GE Healthcare, San Francisco, CA, United States

Recent literature has shown the potential of high‐resolution quantitative susceptibility mapping (QSM) with ultra‐high field (7T) MRI for investigating the magnetostatic properties of brain structures and disease pathology. Higher spatial resolutions, however, require longer scans resulting in a higher likelihood of subject movement. Here, we apply a novel prospective real-time optical motion tracking and correction system using a camera integrated between the Tx and Rx coils of a commercial 7T head coil to demonstrate the feasibility of acquiring high-resolution R2* and QSM images robust to subject motion.

Thomas Ulrich¹, Franz Patzig¹, Bertram Jakob Wilm¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

A single-shot k-space navigator trajectory and a corresponding motion estimation algorithm is proposed. They allow for 3D rigid-body motion estimation. Their performance in terms of accuracy and precision is studied and a cross-validation experiment is conducted to show that the method is suitable for in-vivo use. The accuracy and precision of the method depend on the orbital radius of the navigator. A simulation study is conducted to determine the best choice of the navigator radius.

Malte Hoffmann^1,2, Robert Frost^1,2, David Salat^1,2, M Dylan Tisdall³, Jonathan Polimeni^1,2, and André van der Kouwe^1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ²Department of Radiology, Harvard Medical School, Boston, MA, United States, ³Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States

Volumetric navigators (vNavs) interleaved within longer MRI sequences are an effective method for dynamically detecting and correcting head motion during the acquisition. However, motion is estimated by registering each vNav back to the first, and bias can be introduced by non-rigid deformations of, e.g., the mouth, since the head is taken to be a rigid body. We demonstrate that this bias introduces correction-related artifacts. We present robust real-time brain extraction (0.02 s per vNav) and demonstrate offline that the bias and associated artifacts can be removed by using motion tracks from brain-masked registration.

Hai Luo¹, Meining Chen¹, Ziyue Wu², Bei Lv¹, Fei Peng¹, Shijie Wang¹, Wenkui Hou¹, Weiqian Wang¹, and Gaojie Zhu^1
1AllTech Medical Systems, Chengdu, China, ²Marvel Stone Healthcare, Wuxi, China

Compared with magnitude value, phase of MRI signal is more prone to be influenced by motion. A novel method, sensitivity constrained phase update (sCPU) was proposed for robust and efficient ghost artifacts reduction. Using coil sensitivities as constraints, a synthetic image can be generated in which the ghost is reduced due to phase cancelation. Phase error was first estimated from the raw image and the synthetic image, and then was used to update the phase of raw k-space. The results with simulated and in-vivo data show that the ghost artifacts can be efficiently reduced after several iterations.

Michael Nicholas Hoff¹, Nathan M Cross², Qing-San Xiang³, Daniel S Hippe², Charles G Colip², and Jalal B Andre^2
1Radiology, University of Washington, Seattle, WA, United States, ²Radiology, University of Washington, SEATTLE, WA, United States, ³Radiology, University of British Columbia, Vancouver, BC, Canada

Widespread use of phase-cycled bSSFP imaging is hampered by problematic sensitivity to artifacts caused by susceptibility and motion.  The geometric solution (GS), which can eliminate susceptibility-related banding and signal modulation, has previously show relative insensitivity to motion.  Here, GS-bSSFP is evaluated using a phantom and in humans, imaging the skull base.  The GS mitigates motion artifact in both paradigms and is particularly resilient when one of its four phase cycles is corrupted by motion.

Alessandro Sciarra^1,2, Soumick Chatterjee^2,3, Max Dünnwald^1,4, Oliver Speck^2,5,6,7, and Steffen Oeltze-Jafra^1,5
1MedDigit, Department of Neurology, Medical Faculty, Otto von Guericke University, Magdeburg, Germany, ²BMMR, Biomedical Magnetic Resonance, Otto von Guericke University, Magdeburg, Germany, ³Data & Knowledge Engineering Group, Otto von Guericke University, Magdeburg, Germany, ⁴Faculty of Computer Science, Otto von Guericke University, Magdeburg, Germany, ⁵Center for Behavioral Brain Sciences (CBBS), Magdeburg, Germany, ⁶German Center for Neurodegenerative Disease, Magdeburg, Germany, ⁷Leibniz Institute for Neurobiology, Magdeburg, Germany

Removing motion artifacts in MR images remains a challenging task. In this work, we employed 2 convolutional neural networks, a conditional generative adversarial network (c-GAN), also known as pix2pix, as well as a network based on the residual network (ResNet) architecture, to remove synthetic motion artifacts for phantom images and T1-w brain images. The corrected images were compared with the ground-truth ones in order to assess the performance of the chosen neural networks quantitatively and qualitatively. 

Giulia Di Domenicantonio¹, Nadège Corbin², John Ashburner², Martina Callaghan², and Antoine Lutti^1
1Department for Clinical Neuroscience, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ²Wellcome Centre for Human Neuroimaging, Queen Square Institute of Neurology, UCL, London, London, United Kingdom

Image degradation due to head motion is ubiquitous in MRI, reduces sensitivity, hinders clinical diagnosis and increases the risk of spurious findings. The few existing objective measures of degradation are often used sub-optimally, to remove the most degraded datasets from analysis. Using a large dataset (N~1400) we show how to incorporate an validated index of degradation into the analysis of group studies. The benefit is demonstrated for the case of healthy age-related difference in brain relaxometry data using the SPM software. However, the proposed framework is flexible with broad potential, including the analysis of other metrics and body regions.

Hendrik Mattern¹, Robert Odenbach², Niklas Thoma³, Frank Godenschweger¹, and Oliver Speck^1,4,5,6
1Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany, ²Institute for Medical Engineering, Otto-von-Guericke University, Magdeburg, Germany, ³Department of Mechanical Engineering, Otto-von-Guericke University, Magdeburg, Germany, ⁴German Center for Neurodegenerative Disease, Magdeburg, Germany, ⁵Center for Behavioral Brain Sciences, Magdeburg, Germany, ⁶Leibniz Institute for Neurobiology, Magdeburg, Germany

A low-cost rotation device was designed and built to enable remotely controllable phantom movements. With the device, motions are highly reproducible. For cross-calibrations of external tracking systems, it prevents table movement or the need to move the phantom by hand from inside the scanner during the calibration, reduces the overall calibration duration, and provides similar calibration performance compared to the freehand approach performed by an expert. The CAD model was made publically available.

Seong-Min Kim¹, Phuong Anh Chu Dang¹, Sehong Oh^2,3, and Jang-Yeon Park^1,4
1Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ²Division of Biomedical Engineering, Hankuk University of Foregn Studies, Yongin, Korea, Republic of, ³Imaing Institute, Cleveland Clinic Foundation, Cleveland, OH, United States, ⁴Center for Neuroscience Imaging Research, Suwon, Korea, Republic of

There have been many attempts to separate mixed relaxation-time decays. Among them, some approaches do not assume the number of exponential decays a priori for the analysis of multiple-component decay signals. However, they are sensitive to ill conditions and have a poor resolving ability in terms of decay constants. In this study, a new method is proposed that can analyze multiple T₂ decays with high resolution using the inverse Z-transform, which was demonstrated in simulation and in vivo human brain experiment. T₂-selective images were also presented and used for myelin-water fraction mapping and deep brain-tissue segmentation.

Yichen Hu¹, Qing Wei², Zhongyang Zhou², Jun Xie², and Yongquan Ye^1
1UIH America, Inc., Houston, TX, United States, ²United Imaging Healthcare, Shanghai, China

3D GRASE (GRAdient and Spin Echo) pulse sequence has been widely employed as the readout in arterial spin labeling (ASL) applications, given its efficient acquisition and relatively long lasting signal intensities. However, the inherent weakness of GRASE, such as vulnerability to motions, can induce ghosting artifacts to perfusion imaging and quantitative cerebral blood perfusion (CBF) maps. Herein, we propose applying the Multi-Dimensional Integration (MDI) algorithm to processing the perfusion and CBF maps, by which method noticeable alleviation of motion ghosting can be obtained, and the imaging noise is reduced as well.

Daniel Gordon¹, Allison Blake¹, Liliana Ma¹, Yoshihiro Tanaka¹, Kelvin Chow^1,2, Ning Jin³, Philip Greenland¹, Rod Passman¹, Daniel Kim¹, and Michael Markl^1
1Northwestern University, Chicago, IL, United States, ²Siemens Medical Solutions USA, Inc., Chicago, IL, United States, ³Siemens Medical Solutions USA, Inc., Cleveland, OH, United States

The purpose of this study was to evaluate an efficient, free-breathing, whole-heart 4D flow CS protocol in a cohort of 21 healthy controls. The CS technique was evaluated for internal self-consistency by comparing net flow through various cardiac structures. In addition, cine imaging was performed and used to calculate left ventricular (LV) stroke volume (SV) for comparison to net flow in the ascending aorta. CS whole-heart 4D flow was acquired in 5:23 ± 0:51 minutes. Input and output flow, and LV stroke volume and ascending aorta net volume with 4D flow were significantly (p<0.05) correlated for all comparisons.

SHILPY CHOWDHURY¹, SPENCER LOONG¹, JOAN SABATE¹, and SAMUEL BARNES^1
1LOMA LINDA UNIVERSITY, LOMA LINDA, CA, United States

Running a large longitudinal multi-center study to measure visceral fat and hepatic fat fraction present unique challenges. We scanned fat/water and ex vivo liver phantoms across all sites and over time to show consistency. SliceOmatic and ImageJ were used for quantification of visceral fat and LCModel for hepatic fat fraction. Visceral fat showed a good correlation with hepatic fat and demographics. The use of phantoms and careful design of the protocol can help address challenges of a longitudinal study and help maintain consistency across sites.

Ruyi Zhang¹, Hea Ree Park², Hosung Kim³, Gele Qin¹, Eun Yeon Joo⁴, and Lirong Yan^3
1Department of Electric Engineering, University of Southern California, Los Angeles, CA, United States, ²Inje University College of Medicine, GoyangSouth, Korea, Republic of, ³Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States, ⁴Sungkyunkwan University School of Medicine, Seoul, Korea, Republic of

In this study, we comprehensively studied the regional hemodynamic measures including CBF, cerebral blood volume (CBV), and time-related hemodynamic parameters in OSA patients using Gadolinium contrast agent (Gd)-base dynamic susceptibility contrast MRI.

Alexander Saunders^1,2, Tales Santini³, Tiago Martins³, Howard Aizenstein³, John C. Wood¹, Matthew Borzage (co-corresponding author)¹, and Tamer S. Ibrahim (co-corresponding author)^3
1Children's Hospital Los Angeles, University of Southern California, Los Angeles, CA, United States, ²Rudi Schulte Research Institute, Santa Barbara, CA, United States, ³Swanson School of Engineering and School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States

Ultra-high field time of flight MRA can generate images with higher signal and resolution but image quality may suffer from increased field inhomogeneity. Because we would like to extract arteries for further analysis, we sought to evaluate automatic segmentation performance compared with standard field strength. Five segmentation algorithms were applied to two MRA images (one 3T, one 7T) and performance was measured against manually segmented ground truth data. We found that automatic segmentation performs better in 7T images but confounds in acquisition and image processing need to be further investigated.

Kofi Deh¹, Kristin Granlund¹, Roozbeh Eskandari¹, Arsen Mamakhanyan¹, Nathaniel Kim¹, and Kayvan Keshari,^1
1Memorial Sloan Kettering Cancer Center, New York, NY, United States

We demonstrate the use of a use of a broadband RF excitation with a multi-shot EPI readout for robust separation of metabolites in hyperpolarized 13C imaging. The approach places less demands on scanner hardware and compensates for local B0 inhomogeneity, making it possible to obtain high resolution time-resolved multi-slice imaging over a large region of interest which can be reformatted into 3D volumetric images to facilitate the study diseases such as cancer metastasis using HP probes. 

Zhiyue J Wang^1,2 and Youngseob Seo^3
1University of Texas Southwestern Medical Center, Dallas, TX, United States, ²Children's Health, Dallas, TX, United States, ³Korea Research Institute of Standards & Science, Daejeon, Republic of Korea

In MRI, small signal intensity changes not perceivable by naked eyes are routinely analyzed to extract valuable information, such as in fMRI. However, a small movement was difficult to detect. Recently, image amplification methods have been introduced for visualizing small sub-pixel motions that are too small to be discerned by naked eyes, based on methods developed for video processing. We use computer simulations to explore the range of parameters for the technique to work optimally.

Christian Tönnes¹, Sonja Janssen², Alena-Kathrin Schnurr¹, Tanja Uhrig¹, Khanlian Chung¹, Lothar R. Schad¹, and Frank Gerrit Zöllner^1
1Computer Assisted Clinical Medicine, Mannheim Institute for Intelligent Systems in Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, ²Institute of Clinical Radiology and Nuclear Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany

Perfusion calculation is highly dependent on the expertise and input of the physician and therefore reproduction of the results is difficult. A filter pipeline based algorithm for selecting the AIF ROI was implemented and evaluated. Our results show that such an algorithm can be used to determine the AIF ROI for perfusion calculation in dynamic contrast enhanced MRI images with a high accuracy. A fully automatic and deterministic algorithm removes the need for manual interaction and standardizes clinical perfusion measurements while simultaneously reducing the time requirement for the ROI determination by 86%.

Chang-Beom Ahn¹ and Seong-Jae Park^1
1Kwangwoon University, Seoul, Republic of Korea

We build a deep neural network in time-phase encoding plane (t-y) for compressed sensing cardiovascular CINE MRI. Previously neural networks were developed in cross-sectional image planes (x-y).  A hierarchical convolutional neural network (CNN), known as U-net is used. By adopting the t-y plane, instead of the x-y plane, simultaneous restoration in time and space is effectively achieved. By computer simulation, the proposed deep neural network based on the t-y plane shows better cross-sectional images, clearer temporal profiles, and less normalized mean square errors compared to that of the x-y plane.

Erin J Kelly¹, Hung P Do², Dawn M Berkeley², and Jonathan K Furuyama^2
1Canon Medical Systems USA, Inc, Tustin, CA, United States, ²Canon Medical Systems USA, Inc., Tustin, CA, United States

dDLR algorithms with two path CNN architecture that are designed to be noise adaptive are robust against differences in image contrast and field strength.  This study shows clinical image quality improvement on 1.5T brain and knee datasets using an algorithm trained on 3T data.

Stephen E. Russek¹, Michael A. Boss², H. Cecil Charles³, Andrew M. Dienstfrey¹, Jeffrey L. Evelhoch⁴, Jeffrey L. Gunter⁵, Derek L. G. Hill⁶, Edward F. Jackson⁷, Kathryn E. Keenan¹, Guoying Liu⁸, Michele Martin¹, Nikki S. Rentz¹, Karl F. Stupic¹, Chun Yuan⁹, and Zydrunas Gimbutas^1
1National Institute of Standards and Technology, Boulder, CO, United States, ²American College of Radiology, Philadelphia, PA, United States, ³Duke Image Analysis Laboratory, Durham, NC, United States, ⁴Merck Research Laboratories, West Point, PA, United States, ⁵Mayo Clinic, Rochester, MN, United States, ⁶University College London, London, United Kingdom, ⁷University of Wisconsin, Madison, WI, United States, ⁸National Institute of Biomedical Imaging and Bioengineering, Bethesda, MD, United States, ⁹University of Washington, Seattle, WA, United States

We describe basic scanner characterization and determination of MR-parameter measurement accuracy using the ISMRM/NIST system phantom. The phantom provides a convenient method to measure geometric distortion; the efficacy of non-linear gradient corrections; slice profiles and associated measurement uncertainties; protocol and system dependent resolution contributions; SNR according to NEMA protocols; accuracy of relaxation time; and proton density measurements. The phantom is unique in having SI-traceability, a high level of precision, long-term stability, and monitoring by a national metrology institute.

Mary A McLean^1,2, Scott Hinks³, Joshua Kaggie¹, Ramona Woitek¹, Frank Riemer⁴, Martin Graves¹, Dominick McIntyre², Ferdia Gallagher¹, and Rolf Schulte^5
1Dept of Radiology, University of Cambridge, Cambridge, United Kingdom, ²Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge, United Kingdom, ³GE Healthcare, Waukesha, WI, United States, ⁴MMIV, Dept of Radiology, Haukeland University Hospital, Bergen, Norway, ⁵GE Healthcare, Munich, Germany

Using pulse-acquire spectroscopy, line-shape distortions characteristic of eddy currents were demonstrated for X-nuclei, which were not seen for ¹H, on systems from multiple vendors. The severity of these appeared correlated with the amplitude of the f₀ eddy current frequency compensation term applied by the system along the axis of the applied spoiler gradient. A proposed correction to eddy current compensation taking account of the X-nuclear gyromagnetic ratio was shown to dramatically reduce these distortions on a GE system. The same correction was also shown to improve the quality of non-Cartesian imaging (spirals and cones).

Marta Brigid Maggioni¹, Martin Krämer¹, and Jürgen R. Reichenbach^1,2,3,4
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University, Jena, Germany, ²Michael Stifel Center for Data-driven and Simulation Science Jena, Friedrich Schiller University, Jena, Germany, ³Abbe School of Photonics, Friedrich Schiller University, Jena, Germany, ⁴Center of Medical Optics and Photonics, Friedrich Schiller University, Jena, Germany

B₁ mapping is a major challenge for reliable T₁ quantification, and it is especially difficult for UTE sequences, because most conventional B₁ mapping methods are unable to perform on short T₂^* tissues. Recently, an implementation of the actual flip angle imaging (AFI) method was proposed for UTE sequences. The AFI method requires ideal spoiling of residual transverse magnetization, which is typically achieved by fine-tuning RF-spoiling phase increments as well as the strength of spoiler gradients. In this work, we propose an improved gradient spoiling scheme, which reduces the effect of the RF-spoiling phase increment on the AFI results.

Christoph Zöllner¹, Sophia Kronthaler¹, Stefan Ruschke¹, Jürgen Rahmer², Johannes M. Peeters³, Holger Eggers², Peter Börnert², Rickmer F. Braren¹, and Dimitrios C. Karampinos^1
1Department of Diagnostic and Interventional Radiology, Technical University of Munich, München, Germany, ²Philips Research Laboratory, Hamburg, Germany, ³Philips Healthcare, Best, Netherlands

Stack-of-stars-type radial k-space trajectories employing golden-angle ordering have been becoming popular for either free breathing or navigator-gated volumetric T1-weighted imaging of the abdomen and heart. Most methods for compensating radial k-space trajectory errors induced  by eddy currents and system delays are based either on the acquisition of calibration lines with opposite polarity or on the processing of approximately anti‐parallel spokes from the actual radial acquisition. This work shows that a trajectory correction based on a gradient system impulse response function improves image quality in high-resolution gated golden-angle radial Dixon imaging.

Qi Liu¹, Yuan Zheng¹, Yu Ding¹, Jian Xu¹, and Weiguo Zhang^1
1UIH America, Inc., Houston, TX, United States

A new comprehensive spiral gradient waveform correction strategy is proposed that features multipoint gradient anchoring (MGA). By measuring multiple gradient delays in spiral waveforms at different rotation angles, it effectively ‘anchors’ the waveform at a series of locations and improves gradient waveform fidelity. Application of this innovative design on phantom and volunteer imaging indicates it is an effective and promising technique.

Sascha Brunheim¹, Christian Mirkes², Benjamin E Dietrich², Jolanda M Schwarz¹, Rüdiger Stirnberg¹, Sebastian Ismar³, Alexander Christen³, and Tony Stöcker^1,3
1MR Physics, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²Skope Magnetic Resonance Technologies Inc., Zurich, Switzerland, ³Department of Physics and Astronomy, University of Bonn, Bonn, Germany

An optimized holder for fast mounting of the Skope clip-on field camera into the common Nova Tx/Rx head coil on a 7 Tesla Siemens scanner is presented. Field probe positioning was based on transceiver coil architecture constraints and conditioning for best approximation of field dynamics. The conditioning results for the proposed probe holder positions show very good agreement with the corresponding simulation. They approximate the optimal spherical probe arrangement as well as possible. In comparison, the probe holder outperforms the manual mounting situation conditioning-wise, which corresponds to arbitrary placement onto the receive part of the head coil.

Felix Horger¹, Mathias Nittka¹, and Gregor Körzdörfer^1
1Siemens Healthcare, Erlangen, Germany

Trajectory deformations in non-Cartesian scans can lead to significant image artifacts, while in comparison the effect on Cartesian scans is evidentially minor. We propose a novel approach for trajectory correction relying on the minimization of a suitable measure between a non-Cartesian image and a Cartesian reference image, given a trajectory deformation model. Our proof of concept is applied on simulated as well as measured data. The approach is fast, accurate and easily extendable. Given the right use-case, no extra scan time is required (e.g. mixed spiral-Cartesian MR Fingerprinting).

Filip Szczepankiewicz^1,2,3, Cornelius Eichner⁴, Alfred Anwander⁴, Carl-Fredrik Westin^1,2, and Michael Paquette^4
1Harvard Medical School, Boston, MA, United States, ²Radiology, Brigham and Women's Hospital, Boston, MA, United States, ³Clinical Sciences Lund, Lund University, Lund, Sweden, ⁴Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

Gradient non-linearity distorts the shape of the gradient waveform used for diffuison encoding. This distortion also compromises Maxwell compensation in asymmetric gradient waveforms. We show that one of two strategies for Maxwell compensation fails under non-linear gradiets (K-nulling) whereas M-nulling is immune to this effect.

W Scott Hoge^1,2,3 and Jonathan R Polimeni^2,4,5
1Radiology, Brigham and Women's Hospital, Boston, MA, United States, ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Department of Radiology, Harvard Medical School, Boston, MA, United States, ⁵Massachusetts Institute of Technology, Cambridge, MA, United States

We examine the relationship between traditional 1D linear phase-error correction methods and Dual-Polarity GRAPPA (DPG) for EPI ghost correction. We first show that conventional ghost correction methods based on 1D linear phase errors can be implemented with convolution kernels in k-space, and then generalized in several steps to replicate a typical DPG kernel. We identify that employing multiple phase-encoded lines is important for ghost correction kernel calibration, while incorporating data from multiple channels is critical. Surprisingly, having a kernel extent along the phase-encoded direction is less critical, demonstrating the utility of DPG kernels with limited extent for ghost correction.

Volkert Roeloffs¹, Adam Michael Bush², Suma Anand¹, and Michael Lustig^1
1EECS, UC Berkeley, Berkeley, CA, United States, ²Radiology, Stanford, Stanford, CA, United States

Rosette trajectories are sensitive to gradient delays as caused by eddy currents. Here, we use the RING method recently proposed for radial trajectories to correct for these delays. To this end, we approximate the center portion of the Rosette trajectory to be radial-like, determine delay constants, and correct the entire trajectory in a second step. First phantom and patient studies show that this simple correction method improves image quality in multi-echo Rosette imaging and leads to prolonged T2* values in derived maps. The small amount of required data renders echo-adaptive corrections feasible.   

Paula Ramos Delgado¹, Andre Kuehne², Jason M. Millward¹, Joao Periquito¹, Thoralf Niendorf^1,3, Sonia Waiczies¹, and Andreas Pohlmann^1
1Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany, ²MRI.tools GmbH, Berlin, Germany, ³Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany

Fluorine MR methods support quantification but have inherently low SNR. To enhance sensitivity, SNR-efficient imaging techniques such as RARE and cryogenically-cooled surface RF coils are used. However, transceive surface RF coils show variation in the excitation field, impairing quantification and T₁ contrast. We previously showed improved homogeneity using a novel B₁ correction method developed for ¹H imaging that uses experimental data acquired with a volume resonator. Here, we compared it to a sensitivity-only correction and a combination of both, to evaluate which approach yields the most accurate contrast and concentration quantification. This work is applicable to different nuclei.   

Chen Lin¹, Stephanie Tensfeldt¹, and Christopher Serago^2
1Radiology, Mayo Clinic, Jacksonville, FL, United States, ²Radiation Oncology, Mayo Clinic, Jacksonville, FL, United States

To demonstrate the distortion measurements based on automatic analysis of American College of Radiology (ACR) weekly quality assurance (QA) scans is adequate for monitoring the geometric distortion of a MR scanner for radiation therapy planning by comparing with distortion measurements using a 3D grid phantom.

Bilal Tasdelen^1,2, Alireza Sadeghi-Tarakameh^1,2, Ugur Yilmaz², and Ergin Atalar^1,2
1Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, ²National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey

In simultaneous transmission and reception (STAR), injection of noise and spurs stemming from transmit chain is a problem as well as the leak power. Investigation of noise and spurs are important in order to determine minimum necessary isolation to achieve similar noise levels compared to conventional imaging. Noise sources during STAR are investigated and compared with experiments. It has been shown that using an active cancellation method where dominant noise source is transmit chain, with combination of passive cancellation can reduce noise and spurs. Necessary isolation is shown to depend on input noise and total gain in transmit chain.

Edward M Green^1,2, James C Korte^1,3, Bahman Tahayori^1,4,5, Yasmin Blunck^1,2, and Leigh A Johnston^1,2
1Department of Biomedical Engineering, University of Melbourne, Parkville, Australia, ²Melbourne Brain Centre Imaging Unit, University of Melbourne, Parkville, Australia, ³Department of Physical Sciences, Peter MacCallum Cancer Centre, Parkville, Australia, ⁴Department of Medical Physics and Biomedical Engineering, Shiraz University of Medical Sciences, Shiraz, Iran (Islamic Republic of), ⁵Center for Neuromodulation and Pain, Shiraz, Iran (Islamic Republic of)

Inhomogeneity of the RF transmit field results in undesirable shading and brightening in high field imaging due to range of flip angles across the imaged object. A new method is proposed whereby two image volumes with coarse resolution in the slice direction are acquired at different flip angles and combined to produce an image volume at higher resolution and free of B1 inhomogeneity.  Reconstruction quality is comparable to conventional super-resolution imaging, while image inhomogeneity caused by flip angle error is reduced. This is a flexible method applicable to a range of MRI sequences to correct B1 inhomogeneity.

Daisuke Kokuryo¹, Chika Sato², Takashi Itahashi³, Shigeyoshi Saito⁴, Hiroyuki Ueda¹, Etsuko Kumamoto^1,5, Toshiya Kaihara¹, Nobutada Fujii¹, Noriaki Yahata^2,6, and Ichio Aoki^2,6
1Graduate School of System Informatics, Kobe University, Kobe, Japan, ²National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan, ³Medical Institute of Developmental Disabilities Research, Showa University, Tokyo, Japan, ⁴Graduate School of Medicine, Osaka University, Suita, Japan, ⁵Information Science and Technology Center, Kobe University, Kobe, Japan, ⁶Institute for Quantum Life Science, National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan

Establishing data harmonization in fMRI “big data” is necessary to ensure the reliability and reproducibility of fMRI research. Our group recently developed two distinct phantoms: a brain-shaped phantom to correct field heterogeneity and a functional image-specific phantom to calibrate shape distortion and signal irregularity. A preliminary experiment confirmed a shape distortion and signal irregularity caused by field inhomogeneity when using EPI signals, and these were corrected using an affine transformation. Therefore, our developed phantoms have the potential to contribute to achieving fMRI data standardization.

Tzu-Cheng Chao¹, Dinghui Wang¹, Guruprasad Krishnamoorthy², and James G. Pipe^1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States, ²Philips Healthcare, Gainesville, FL, United States

Deblurring with water/fat separation plays a critical role in spiral imaging. The reconstruction quality depends on good off-resonant frequency estimation. A field map before each spiral imaging exam is often acquired to approximate the B₀ of the scanned subject. However, the estimation errors occur due to nonconcurrent collection of the imaging data. The proposed work introduces an iterative method to update the field map based on the acquired images to improve spiral image reconstruction. The results have shown that the blurring can be reduced along with improved fat/water separation after updating the reference B₀ used for reconstruction.

Franz Patzig¹, Bertram Wilm¹, Simon Gross¹, David Brunner¹, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland

We present a novel algorithm capable of determining a B0 map and an off-resonance corrected reconstructed image from a single-shot acquisition. The functionality of the algorithm was shown in-vivo for multiple imaging geometries using regular undersampled single-shot EPI and Spiral readouts showing stable convergence. In addition, the method is tested for the common situation of inter-scan subject movement, in which pre-acquired field maps would be rendered invalid.

Qing-San Xiang¹ and Michael Nicholas Hoff^2
1Radiology, University of British Columbia, Vancouver, BC, Canada, ²Radiology, University of Washington, Seattle, WA, United States

Phase-Cycled (PC) bSSFP imaging is useful for qualitative and quantitative studies of tissue. But the images generated should be properly combined when they are acquired with multiple receiver coils; in particular, phase information in the complex images must be preserved. We describe a straightforward yet optimal coil combination algorithm for PC-bSSFP applications, where the phase is preserved through relative phase alignment along the measurement dimension. The method is demonstrated with experimental results from phantom and volunteer scans.

Uten Yarach^1,2, Matthew Bernstein¹, John Huston III¹, Norbert Campeau¹, Petrice Cogswell¹, Daehun Kang¹, Myung-Ho In¹, Yunhong Shu¹, Nolan Meyer¹, Erin Gray¹, and Joshua Trzasko^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai, Thailand

A recently proposed model-based iterative reconstruction (MBIR) method enables to prospectively manage B0-inhomogeneity and gradient-nonlinearity in EPI, and has been demonstrated to generate images with high SNR and minimal spatial blurring and geometric distortion. However, the clinical significance and degree of benefit remains undetermined. In this study, using commodity EPI acquisition protocols for whole-brain imaging, MBIR was radiologically compared against standard scanner-generated EPI images and post-processed versions. The results show that significant advantage of MBIR (p<0.05) over both the standard scanner-generated EPI results and post-processed variants was observed in three categories: SNR, geometric accuracy, and overall image quality.
 

Uten Yarach^1,2, Matthew Bernstein¹, John Huston III¹, Myung-Ho In¹, Yi Sui¹, Daehun Kang¹, Yunhong Shu¹, Erin Gray¹, Nolan Meyer¹, and Joshua Trzasko^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai, Thailand

Single-polarity reference scan-based paradigms are routinely used to combat Nyquist ghosting artifacts, they often fail to the fully suppress them because of statistical biases in estimated correction coefficients that result from noise and off-resonance effects. Prior work has shown that use of dual-polarity reference scans can mitigate the latter. In this work, we propose that this concept can be generalized to enable robust Nyquist ghost correction (NGC) directly from two reversed-readout EPI acquisitions – without explicit reference scanning. In-vivo results show the similar trends as in phantom examples, with the proposed-NGC mitigating aliasing artifacts representing up to 20% intensity errors.
 

Michael Mullen¹ and Michael Garwood^1
1Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States

Clinical MRI sequences for imaging near metallic implants are mainly multi-spectral approaches, with fast spin-echo acquisitions to achieve clinically relevant scan times. Due to the large bandwidths necessary for refocusing all off-resonance spins near metallic implants, usually the refocusing pulse flip angles must be limited to a sub-optimal value to permit a safe specific absorption rate.  Here, a low peak amplitude, radiofrequency refocused sequence is used to limit energy deposition. Reversed encoding is employed, where two acquisitions are collected with opposite frequency-encoding gradient polarity. An estimate of the displacement field is found using a B-spline basis and the magnitude images.

Naveen Bajaj¹, Jaladhar Neelavalli¹, Rupesh VK¹, Karthik Gopalakrishnan¹, and Marc Van Cauteren^2
1Philips Healthcare, Bangalore, India, ²Philips Healthcare, Tokyo, Japan

A novel approach for mitigating artifacts from localized motion of the eye, during interleaved multi-shot diffusion weighted imaging, is presented. A 2D cylindrical spatial saturation pulse is used to suppress signal from the orbit region, thereby significantly suppressing the ghost artifacts from eye movement in low b-value images. The saturation being localized to the orbit region does not influence the surrounding tissues. Placement of such a cylindrical pulse on the orbit region is relatively straight forward. In addition, the total scan time is not significantly affected by the cylindrical pulse saturation.

Alexander R Toews^1,2, Philip K Lee^1,2, Daehyun Yoon¹, and Brian A Hargreaves^1,2,3
1Radiology, Stanford University, Stanford, CA, United States, ²Electrical Engineering, Stanford University, Stanford, CA, United States, ³Bioengineering, Stanford University, Stanford, CA, United States

Imaging near metal is challenging due to severe metal-induced field inhomogeneities. Multispectral imaging sequences employ view-angle tilting (VAT) to correct in-plane distortions due to nearby metal at the expense of blurring the entire image. We exploit the additional phase-encoding dimension acquired in multispectral imaging in order to reduce the VAT-induced blur. The method primarily consists of regridding k-space measurements to avoid the VAT-induced shear. Results on a grid phantom demonstrate the ability of this method to reduce readout blur. This work highlights an important limitation of VAT and demonstrates strategies for mitigating this effect.

Anjali Datta¹, Dwight Nishimura¹, and Corey Baron^2
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Medical Biophysics, Western University, London, ON, Canada

For banding-free cardiac cine bSSFP imaging, we present a non-Cartesian accelerated frequency-modulated sequence that acquires three phase-cycles within a short breath-hold.  A projection-reconstruction trajectory is used and data is also acquired on the rewinds, enabling generation of a B₀ field map using BMART.  This facilitates field-map combination of the phase-cycle images, which results in more homogeneous blood pool and reduced signal contributions from out-of-slice spins than root-sum-of-squares.

Robert Frost^1,2, Divya Varadarajan^1,2, Jesper Andersson³, Jonathan R Polimeni^1,2, Bruce Fischl^1,2,4, and André J. W. van der Kouwe^1,2
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Department of Radiology, Harvard Medical School, Boston, MA, United States, ³Wellcome Centre for Integrative Neuroimaging, University of Oxford, Oxford, United Kingdom, ⁴Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA, United States

Readout distortion can affect structural imaging with MPRAGE particularly in temporal regions. Interleaved readout polarity MPRAGE allows for estimation of distortion without motion confound between oppositely distorted images. This approach could be useful for single echo MPRAGE imaging with ~200 Hz/px.

Jie Wen¹, Dmitriy A Yablonskiy², Alexander L Sukstanskii², Feiyan Zeng¹, and Ying Liu^1
1Radiology, The First Affiliated Hospital of USTC, Hefei, China, ²Radiology, Washington University in St. Louis, St. Louis, MO, United States

Macroscopic B0 magnetic field inhomogeneity adversely affects Gradient-Recalled-Echo (GRE) MRI images. A previously introduced voxel spread function (VSF) method has been proposed to correct for these adverse effects if data are acquired using multi-GRE (mGRE) sequences. The method accounts for both, through-slice and in-slice field inhomogeneities and accounts for between-voxel signal propagation effects. The direct voxel-wise VSF calculation requires long computation time. We propose a library-driven approach for the VSF calculation that significantly reduces computation time, thus providing a platform for the applications of mGRE-based quantitative techniques in clinical practices.

Venkata Veerendranadh Chebrolu^1,2, Stefan Sommer^3,4, Constantin von Deuster^3,4, and Julien Galley^5
1Siemens Medical Solutions USA, Inc., Rochester, MN, United States, ²Department of Radiology, Mayo Clinic, Rochester, MN, United States, ³Siemens Healthcare AG, Zurich, Switzerland, ⁴SCMI, Swiss Center for Musculoskeletal Imaging, Zurich, Switzerland, ⁵Department of Radiology, Balgrist University Hospital, University of Zurich, Zurich, Switzerland

Ultra-high field (UHF) 7T MRI provides high spatial resolution with significantly better signal-to-noise ratio compared to 3T and C-spine imaging at 7T is being pursued at a few research sites across the globe. MRI of the C-spine at 7T is challenging due to multiple factors.  Recently, an algorithm ‘Uniform Combined Reconstruction’ (UNICORN) was used to correct receive-coil intensity inhomogeneity and improve the uniformity and overall image quality of 7T knee MRI. In this work, we present preliminary results from the application of UNICORN to C-spine imaging and demonstrate the utility of UNICORN in improving uniformity of C-spine MRI at 7T.

Simon Shah¹, Fran Padormo ¹, Kristine Knott¹, Suki Thomson¹, Steve Conner¹, Geoff Charles-Edwards¹, and Phil Touska^1
1Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom

Neurofibromatosis type 2 (NF2) patients commonly have bilateral vestibular schwannomas, which typically require regular monitoring with MRI. However these patients also have cochlear implants which makes MRI challenging. We have used Slice Encoded Metal Artefact Correction (SEMAC) to improve the imaging of IAMs in patients with cochlear implants in-situ. The implementation of SEMAC imaging reduced the geometric distortion and the volume of the signal void around the implants by over half. 

Sina Tafti¹, John P Mugler III², Kevin Vu¹, William J Garrison³, and G Wilson Miller^2
1Department of Physics, University of Virginia, Charlottesville, VA, United States, ²Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, United States, ³Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, United States

Multi-spectral imaging techniques such as MAVRIC, SEMAC, and MAVRIC SL based on 3D TSE sequence significantly reduce metal artifacts. MAVRIC and MAVRIC-SL techniques traditionally employ Gaussian RF pulses to achieve an optimal sum of squares composite image while SEMAC uses windowed-sinc RF pulses. In this work, we implement multi-spectral acquisition into the variable flip-angle TSE with hard RF pulses which yields a desirable sum of squares composite image while achieving high turbo-factor and minimal echo spacing in imaging near metallic screws in phantom and an ex vivo lamb leg.

Kilian Stumpf¹, Andreas Horneff¹, Jan-Bernd Hövener², and Volker Rasche^1
1Department of Internal Medicine II, University Medical Center Ulm, Ulm, Germany, ²Department of Radiology and Neuroradiology, University Medical Center Kiel, Kiel, Germany

Artifacts due to the presence of metallic dental materials often limit the application of MRI. These materials, such as dental implants or fillings, often cause substantial artifacts e.g. in the oral cavity impairing diagnostic accuracy. In this contribution, we present an approach for conducting spin-echo based sequences with significantly reduced flip angles and high excitation bandwidths of up to 17 kHz by using an inductively coupled local coil, which in combination with single-point methods enables almost completely artifact-free local imaging of e.g. dental titanium implants.

Jee Won Kim¹, Kinam Kwon², Byungjai Kim¹, Sunho Kim¹, and Hyunwook Park^1
1Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, Republic of, ²Samsung Advanced Institute of Technology (SAIT), Suwon, Korea, Republic of

We propose a new scheme for EPI distortion correction, which implements unsupervised learning, trained with readily available images, such as ImageNet2012 dataset. The distortion-corrected image is obtained by the MR image generation function using the input distorted images and the frequency-shift maps that are the outputs of the network. Two distorted images obtained with dual-polarity phase-encoding gradients are the inputs of the neural network. The neural network estimates the frequency-shift maps from the distorted images. To train the neural network, unsupervised learning was conducted by minimizing the L1 loss between input distorted images and the estimated distorted images.

Natalie Bnaiahu¹, Ella Wilczynski¹, Shir Levy², Noam Omer¹, Tamar Blumenfeld-Katzir¹, and Noam Ben-Eliezer^1,3,4
1Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, ²School of Chemistry, Tel Aviv University, Tel Aviv, Israel, ³Sagol school of Neuroscience, Tel Aviv University, Tel Aviv, Israel, ⁴Center for Advanced Imaging Innovation and Research, New York, NY, United States

On high-field scanners, strong imaging gradients induce spurious diffusion signal decay, which distorts qT₂ calculation. By modeling the pulse sequence gradients and coherence pathways, an effective b value was calculated to assess signal attenuation caused by diffusion. ADC values were measured, extensive phantom scans and in-vivo experiments were performed using the MSME protocol with varied voxel sizes to examine the effect and the solution. Before correction T₂ values were short with high variability across different voxel sizes, after correction T₂ values increased and became more accurate and consistent. Tissue properties also influenced the correction as their ADC varies.

Jakob Meineke¹ and Tim Nielsen^1
1Philips Research, Hamburg, Germany

A reconstruction method is presented to reduce off-resonance induced artifacts in gradient-echo MRI. The method reconstructs the magnetization without the off-resonance induced phase and in this way reduces the effects of intra-voxel dephasing. The method is applied to simulations and volunteer scans, showing reduced signal voids and improved homogeneity in R2*-maps.

Kerrin J Pine¹, Luke J Edwards¹, and Nikolaus Weiskopf^1
1Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

In gradient echo imaging sequences, transverse coherences persisting across repetitions must be managed to avoid large variations in the steady state signal. Ultra-high amplitudes for gradient spoiling can be effective, however, conventional human MR scanners do not achieve the necessary gradient amplitudes. By using a 3T Connectom MRI scanner with a 300 mT/m gradient amplitude, we demonstrate that by operating in the diffusion spoiling regime, it is now possible to eliminate the contribution of unwanted transverse magnetization to the steady state by gradient spoiling alone. It can serve as a reference standard for validating spoiling schemes and for R1 quantification.

Marina Manso Jimeno^1,2, Sairam Geethanath^1,2, and John Thomas Vaughan Jr.^1,2
1Columbia University, New York, NY, United States, ²Columbia Magnetic Resonance Research Center (CMRRC), New York, NY, United States

3DANCE is a sequence designed to be a good candidate for a whole-body sequence for multiple applicaitons. Phantom and in vivo experiments demonstrated a good spatial resolution and consistent ability to separate water and fat tissues. Off-resonance correction of the water and fat images have showed good results in vitro but needs more testing for in vivo datasets. Future steps include improving the robustness of the methods and testing for motion tolerance.

Silu Han¹, Mahesh Bharath Keerthivasan², Chidi Patrick Ugonna¹, and Nan-kuei Chen^1
1Biomedical Engineering Department, The University of Arizona, Tucson, AZ, United States, ²Medical Imaging Department, The University of Arizona, Tucson, AZ, United States

A coil-signature-based phase cycled correction method has been developed for Nyquist artifact removal in echo planar imaging (EPI).  In our study, we investigated a novel coil-signature-based Nyquist artifact correction method that can be applied to EPI integrating various acceleration schemes including through-plane Multi-band Imaging (MB) and in-plane parallel SENSitivity Encoding Imaging (SENSE). Our method uses a coil-signature-based phase-cycled reconstruction without requiring EPI reference scans, and can inherently correct 2D phase errors. Our results show that the developed method can effectively reduce EPI Nyquist artifacts under different acceleration approaches.

M. Dylan Tisdall^1
1Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States

N/2 ghosts in EPI result from consistent discrepancies between readouts with positive and negative polarities. We present 3D EPI with scrambled readout polarities as a strategy to reduce the coherence of N/2 ghosts in 4D x-f space and reduce their impact on quantitative analyses (e.g., motion tracking or resting state fMRI). We demonstrate that the method can produce either individual volumes with N/2 ghost energy spread out in the partition direction, or complete 4D x-f data with ghosts spread in both partition and frequency directions.

Christopher T Sica¹, Navid Pourramzan Gandji², and Qing X Yang^2
1Radiology, PennState University College of Medicine, Hershey, PA, United States, ²Neurosurgery, PennState University College of Medicine, Hershey, PA, United States

We performed a study to assess the effects of ultra-high dielectric constant material (uHDC) on the static field homogeneity at 3T. We characterized these effects on both a spherical and body phantom with 3D off-resonance field mapping and balanced SSFP imaging. The static field experienced shifts of up to 100 Hz in the presence of uHDC monolithic blocks. Shimming was able to partially compensate for these shifts. Future studies incorporating these materials should take their susceptibility effects into account.

Simon Shah¹, Danoob Dalili², Jan Fritz ³, Geoff Charles-Edwards¹, and Amanda Isaac^1
1Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom, ²King's College London, London, United Kingdom, ³Johns Hopkins University, Baltimore, MD, United States

Musculoskeletal (MSK) imaging of patients with hip implants can be challenging due to metal artefacts. We have quantitatively assessed a number of metal artefact reduction sequences (MARS) on commonly implanted hip implants. The MARS methods used were: high receiver bandwidth, high transmit bandwidth, view angle titling (VAT) and slice encoded metal artefact correction (SEMAC). Signal pile-up and voids were most reduced across implants when SEMAC was employed and also artefacts at the bone metal interface were reduced.

Kohei Yuda¹, Takashige Yoshida¹, Masami Yoneyama², Yuki Furukawa¹, and Nobuo kawauchi^1
1Tokyo Metropolitan Police Hospital, Nakano, Japan, ²Philips healthcare, Tokyo, Japan, minato, Japan

The conventional Dual Inversion Recovery T2-weighted Black Blood (c-DIR-BB) on myocardial MRI is useful for the clinical diagnosis. One of the problems of c-DIR-BB is aliasing artifact, resulting in degradation of image quality. The zoomed method for improved aliasing artifact, orthogonal selection (i.e. phase / slice direction) excites to suppress tissue signals outside with a smaller FOV in phase encoding direction. Hence the DIR-BB using zoomed methods was improved image quality by orthogonal select excitation RF pulse.

Hamzeh Ahmad Mohammad Al Masri^1,2,3, Tonima Ali¹, Katie McMahon⁴, and Markus Barth^1,3,5
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²Medical Imaging Department, The Hashemite University, Al-Zarqa, Jordan, ³ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia, ⁴Royal Brisbane & Women's Hospital, Queensland University of Technology, Brisbane, Australia, ⁵School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia

Quality assurance (QA) is mandatory to ensure the stable performance of MR scanners over time. Automated analysis of QA tests can be useful to increase operator efficiency and overcome the manual processing issues such as time constraints and human bias. In this paper, we compare the manual and automated analysis approaches of the QA image datasets that have been collected from 3T MRI scanners using the American College of Radiology (ACR) accreditation phantom. We found that the automated method can significantly reduce the QA analysis time and the results of both methods were in agreement with each other.

Yan Wu¹, Yajun Ma², Jiang Du², and Lei Xing^1
1Radiation Oncology, Stanford University, Stanford, CA, United States, ²Radiology, University of California San Diego, La Jolla, CA, United States

Inhomogeneity of the radiofrequency field (B1) is one of the main problems in quantitative MRI. Leveraging from the unique ability of deep learning, we propose a data driven strategy to derive quantitative B1 map from a single qualitative MR image without specific requirements on the weighting of the input image. B1 estimation is accomplished using a self-attention deep convolutional neural network, which makes efficient use of local and non-local information. Without additional data acquisition, an accurate estimation of B1 map is achieved, which is useful for the compensation of field inhomogeneity in T1 mapping as well as for other applications.  

Lili Wang¹, Fanwen Wang¹, Yinghua Chu², Xucheng Yu¹, Chengyan Wang³, and He Wang^1,3
1Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China, ²MR Collaboration, Siemens Healthcare Ltd., Shanghai, China, ³Human Phenome Institute, Fudan University, Shanghai, China

The commonly used approach of Nyquist ghost correction in echo planar imaging (EPI) include linear phase correction and model-free 2D phase correction. The recent proposed method termed ‘PEC-SENSE’ incorporates 2D phase error correction with parallel imaging can robustly eliminate Nyquist ghost for EPI data，while does not act well when a distortion mismatch exsisted between the calibration data and image data. The proposed model-based deep learning method can obtain more robust phase maps than PEC-SENSE to remove image ghost and preserve the image SNR in low or high-accelerated EPI data.

John Austin Roberts¹, Henrik Odeen¹, Sunil Patil², Waqas Majeed², Bradley Bolster³, Himanshu Bhat⁴, and Dennis L Parker^1
1Radiology and Imaging Sciences, University of Utah, Salt lake City, UT, United States, ²Siemens Medical Solutions USA, Inc, Baltimore, MD, United States, ³Siemens Medical Solutions USA, Inc, Salt Lake City, UT, United States, ⁴Siemens Medical Solutions USA, Inc, Boston, MA, United States

In magnetic resonance thermometry based on proton resonance frequency shift, temperature is computed based on changes in phase as measured: with respect to previously acquired images (baselines); between regions within the same image (referenceless); or some hybrid of the two approaches. In phase reconstruction algorithms, how multi-coil data is combined affects both computational efficiency and temperature measurement precision.  We modify a hybrid thermometry phase reconstruction algorithm to test several coil combination methods for computational efficiency and to evaluate their effect on temperature measurement precision.  Results suggest applying coil-combination prior to phase extraction both for efficiency and SNR.

Diana Bencikova^1,2, Stephan Kannengiesser³, Gert Reiter⁴, Ahmed Ba-Ssalamah¹, Siegfried Trattnig^1,2, and Martin Krššák^2,5
1Department of Radiology, Medical University Vienna, Vienna, Austria, ²Christian Doppler Laboratory for Clinical Molecular Imaging, MOLIMA, MUW, Vienna, Austria, ³Siemens Healthcare GmbH, Erlangen, Germany, ⁴Siemens Siemens Healthcare Diagnostics GmbH, Graz, Austria, ⁵Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Vienna, Austria

Radial T₂ mapping of the liver is fast and motion insensitive, which is ideal for clinical applications. Here we tested a prototype radial turbo-spin-echo sequence for T₂ mapping of the liver in phantoms and in-vivo in patients. In the phantoms we compared it to conventional Cartesian multi-SE sequence and tested the effect of fat suppression by comparing fat-suppressed and fat-unsuppressed values. From the patient evaluation, comparing it to single-voxel multi-echo MRS, we proved it to be suitable for clinical applications and a promising tool for characterization of diffuse liver disorders, but there are systematic differences between different methods.  

Ke Jiang¹, Jiazheng Wang¹, and Xiaofang Xu^1
1Philips Healthcare Greater China, Beijing, China

T1-weighted imaging is a necessary component of clinical brain MR to provide anatomical information at high spatial resolution. T1w brain image in clinical practice is regularly acquired with two-dimensional turbo-spin-echo sequence, which suffers from the pulsation artifacts in the phase-encode direction from superior sagittal sinus, the straight sinus, and the sigmoid sinus. This study exploits the spiral trajectory for the spin-echo sequence to achieve the T1 weighting and to avoid the pulsation artifacts.