Artifacts & Motion Correction
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Thursday May 12th
Room 513A-D  16:00 - 18:00 Moderators: Joseph Hajnal and Claudia del Carmen Prieto

16:00 641.   Improving Scan Efficiency of Respiratory Gated Imaging Using Compressed Sensing with 3D Cartesian Golden Angle Sampling 
Mariya Doneva1, Christian Stehning1, Kay Nehrke1, and Peter Börnert1
1Philips Research Europe, Hamburg, Germany

Navigator gating is used to reduce motion artifacts during free breathing MRI. To cope with temporal changes of the breathing pattern the PAWS method was proposed using multiple gating bins. The final image is reconstructed from the bin that is completely filled first. All other data are discarded. In this work, we propose a method for improving the efficiency of respiratory gated imaging by using all acquired data in the reconstruction. The method is based on 3D Cartesian golden angle sampling and applies compressed sensing for the reconstruction of images from incompletely sampled bins. Image registration is used to combine the data in the final reconstruction step.

16:12 642.   Metric Optimized Gating for Fetal Cardiac Imaging 
Christopher William Roy1, Mike Seed2, Joshua F van Amerom1,3, Lars Grosse-Wortmann2,3, Shi-Joon Yoo2,3, and Christopher K Macgowan1,3
1Departments of Medical Biophysics and Medical Imaging, University of Toronto, Toronto, Ontario, Canada, 2Division of Cardiology, Department of Paediatrics, The Labatt Family Heart Centre, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada, 3Department of Diagnostic Imaging, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada

A metric-based image reconstruction method is introduced for fetal myocardial imaging. This method, known as metric optimized gating (MOG), is adapted from a previous study of fetal blood flow. It involves oversampling k-space and then reconstructing images according to an iterative heart-rate model until an image metric is minimized (spatial entropy). The accuracy of this approach in the presence of heart-rate variability is investigated through numerical simulation, and the benefit of higher-order heart-rate models is also presented. Finally, MOG results from a healthy adult volunteer are compared directly to those using direct ECG gating to test feasibility in vivo.

16:24 643.   3D Non-Rigid Motion Modeling of the Liver from Undersampled Golden-Radial Phase Encoding (G-RPE) Acquisitions 
Christian Buerger1, Andrew Peter King1, Tobias Schaeffter1, and Claudia Prieto1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom

We propose a method to determine a 3D non-rigid motion model of the liver from a free-breathing MR acquisition. Multiple 3D near motion-free respiratory phases of an average breathing cycle are acquired by taking advantage of the recently introduced self-gated Golden-Radial Phase Encoding (G-RPE) trajectory. Non-rigid image registrations followed by time-wise motion field interpolations are applied to model the continuous deformation of the highest quality image to all other phases allowing us to predict any respiratory phase at arbitrary respiratory positions between end-exhale and end-inhale. The proposed approach was validated on 5 volunteers achieving target registration errors of 1.83mm.

16:36 644.   From Artifact to Merit: Cardiac Gated MRI at 7T and 3T Using Magneto-Hydrodynamic Effects for Synchronization 
Tobias Frauenrath1, Matthias Dieringer1,2, Nishant Patel1, Celal Özerdem1, Jan Hentschel1, Wolfgang Renz1,3, and Thoralf Niendorf1,2
1Berlin Ultrahigh Field Facility, MDC Berlin, Berlin, Germany, 2Charité Campus Buch, Humboldt-University, Experimental and Clinical Research Center (ECRC), Berlin, Germany, 3Siemens Healthcare, Erlangen, Bayern, Germany

ECG is corrupted by magneto-hydrodynamic effects at higher magnetic field strength. Artifacts in the ECG trace and severe T-wave elevation might be mis-interpreted as R-waves. MHD being inherently sensitive to blood flow and blood velocity provides an alternative approach for cardiac gating, even in peripheral target areas far away from the commonly used upper torso positions of ECG electrodes. This feature would be very beneficial to address traveling time induced motion artifacts and trigger latency related issues raised by ECG-gated peripheral MR angiography. For all those reasons, this work proposes the use of MHD-trigger for cardiac gated MR.

16:48 645.   Steady-State B1 mapping of dynamically changing RF fields 
Shaihan J Malik1, Francesco Padormo1, and Joseph V Hajnal1
1Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, London, United Kingdom

Actual flip angle imaging (AFI) is a fast B1 mapping method consisting of a steady-state spoiled gradient echo imaging sequence with TR periods of alternating duration. Temporal variation of B1 field is known to occur due to, for example, physiological motion and it would be desirable to measure these variations or to avoid artifacts resulting from them. We have studied the behaviour of the AFI sequence’s steady-state in response to oscillatory B1 field amplitudes, using both simulation and experiment, and show that under certain conditions such modulations can be faithfully measured using AFI.

17:00 646.   Frequency correction for MR Spectroscopy in the human breast at 7 Tesla with external field monitoring 
Bart Lowie van de Bank1, Vincent Oltman Boer1, Mariska P Luttje1, Jannie Petra Wijnen1, Gerard van Vliet1, J M Hoogduin1, Peter R Luijten1, and Dennis W. Klomp1
1Beeld, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

Variations in the frequency of the main magnetic field hamper applications in MR imaging and spectroscopy. We demonstrate the feasibility of real time observation of B0 fluctuations in the human breast with a field probe at a 7T MR system. In addition, we demonstrate that direct observation of field distortions may substantially improve frequency correction, compared to the indirect calibration method based on respiratory belt synchronization. The field probes can be used to accurately and directly measure dynamic frequency offsets caused by breathing.

17:12 647.   Real Time Dynamic Shimming for MR Spectroscopy Using 2-dimensional Rf Excitations 
Brian Keating1, and Thomas Ernst2,3
1Deptartment of Medicine, University of Hawaii, Honolulu, HI, United States, 2Department of Medicine, University of Hawaii, Honolulu, HI, United States, 3University of Hawaii

Patient motion can compromise the shim quality in MR spectroscopy. Therefore, we incorporated a dynamic shimming module into the “dead time” in a standard PRESS sequence. 2-dimensional spatial rf pulses excite 3 columns, parallel to the coordinate axes. Two echoes are read out for each column along the direction of the column axes. One-dimensional field maps are computed for each column. Shim corrections are fed back into the sequence, where they are applied as shim gradients during the following PRESS read out. Phantom and in vivo experiments confirm that dynamic shimming improved spectral quality in the presence of B0 inhomogeneities.

17:24 648.   Bowtie PROPELLER: A fast and efficient motion correction method in MRI 
Hisamoto Moriguchi1,2, Shin-ichi Urayama3, Yutaka Imai1, Manabu Honda4, and Takashi Hanakawa4,5
1Radiology, Tokai University, Isehara, Kanagawa, Japan, 2Radiology, Hiratsuka municipal hospital, Hiratsuka, Kanagawa, Japan, 3Human Brain Research Center, Kyoto University, Kyoto, Kyoto, Japan, 4Functional Brain Research, National Center of Neurology and Psychiatry, Kodaira, Tokyo, Japan, 5Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Japan

PROPELLER has shown to have significantly reduced sensitivity to motion artifacts. A primary disadvantage of PROPELLER is extended scan time. In this study, a novel sampling and reconstruction technique that can significantly reduce the scan time of PROPELLER has been demonstrated. This new technique is referred to as ebowtie PROPELLERf since the shape of each blade appears to be a ebowtief. The total scan time of bowtie PROPELLER is usually shorter than 50% of the conventional PROPELLER. Bowtie PROPELLER is a very useful motion correction technique with reduced scan time while maintaining the image quality.

17:36 649.   Prospective Motion Correction for Diffusion Imaging Using FID Navigators 
Tobias Kober1,2, Rolf Gruetter1,3, and Gunnar Krueger2
1Laboratory for functional and metabolic imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 2Advanced Clinical Imaging Technology, Siemens Suisse SA - CIBM, Lausanne, Switzerland, 3Departments of Radiology, Universities of Lausanne and Geneva, Switzerland

17:48 650.   A Robust MR-based Rigid-Body Motion Correction for Simultaneous MR-PET  -permission withheld
Marcus Goerge Ullisch1, Christoph Weirich1, Juergen Scheins1, Elena Rota Kops1, Avdo Celik1, Tony Stöcker1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

Motion poses a significant problem for PET imaging. Here, we present an MR-based rigid-body motion correction approach for neurological MR-PET studies with hybrid MR-PET scanners. Motion data are extracted from an EPI time-series and are used to correct the PET images for motion with minimal additional processing time required. Preliminary in vivo results show a clear resolution recovery in the PET images.