|Motion Artifact Correction|
An Alternative Concept of Non-Sequence-Interfering
Patient Respiration Monitoring
Ingmar Graesslin1, Dennis Glaesel1, Peter Börnert1, Henry Stahl1, Peter Koken1, Kay Nehrke1, Henk Dingemans2, Giel Mens2, Jürgen Götze3, Paul Harvey2
1Philips Research Europe, Hamburg, Germany; 2Philips Medical Systems, Best, Netherlands; 3TU Dortmund, Dortmund, Germany
Patient motion is still challenging in MRI, especially in the abdominal region. The use of advanced motion artifact reduction techniques can improve diagnostic image quality. Motion sensing and correction approaches cope with this problem. However, e.g. navigators influence the steady state of SSFP sequences and are, therefore, not inherently compatible with this technique. This paper describes the application of respiratory motion detection from changes of the coil properties for steady state imaging, using a simple retrospective gating approach. Motion information is obtained in real-time. The method is compatible with almost any pulse sequence and no extra patient preparation is necessary.
Prospective Self-Gating for Simultaneous Compensation
of Cardiac and Respiratory Motion
Jelena Curcic1, Martin Buehrer1, Peter Boesiger1, Sebastian Kozerke1
1Institute for Biomedical Engineering, ETH Zurich, Zurich, Switzerland
A prospective self-gated approach for time-efficient free breathing cardiac imaging was successfully implemented and evaluated. Motion data needed for synchronization were accurately extracted in real-time from the repeatedly acquired k-space center thereby eliminating the need for external cardiac and respiratory signal detection. Using real-time filtering, cardiac and respiratory variations were separated and used for prospective triggering and gating. Image quality obtained with the proposed method was found to be comparable to the ECG triggered breathheld acquisitions as well as retrospective self-gating methods. The scan efficiency however could be significantly increased with respect to retrospective self-gating.
A New Respiratory Gating Technique for
Whole Heart Cine MRI
Sergio Andres Uribe1, Tarinee Tangcharoen1, Reza Razavi1, Tobias Schaeffter1
1Kings College London, London, UK
In this work we present a new respiratory gating technique for whole heart cine imaging. In this approach, we integrate the acquisition of an extra “slice navigator” within a b-SSFP sequence. The slice navigator in conjunction with a dedicated coil to read out the navigator signal makes the respiratory navigation more robust and sensitive to motion. A breathing signal was derived and used to gate the scan, which drastically reduced motion artifacts. The acquisition requires minimal planning and allows us to reformat the data in any view. The method represents a step forward for an easier cardiac MR examination.
Spherical Navigator Echoes Using GRAPPA for Rapid 3D
Rigid-Body Motion Detection
Junmin Liu1, Maria Drangova1
1Imaging Lab, Robarts Research Institute, Schulich School of Medicine, University of Western Ontario, London, Canada
The spherical navigator echo (SNAV) is ideal for tracking rigid body motion in all six degrees of freedom simultaneously. However, the relatively long time required to acquire a spherical navigator echo limits the utility of SNAV for short TR pulse sequence used in cardiac and functional MRI. A parallel imaging approach, based on the generalized auto calibrating partially parallel acquisition (GRAPPA) algorithm, was implemented to speed up SNAV acquisition. Using this SNAV-GRAPPA approach, hemispherical SNAV trajectories could be acquired as fast as 2.5 ms (at a bandwidth of 125kHz) with and acceleration factor R=4 while maintaining accuracy.
Real-Time Navigator Processing Using Kalman Filtering
Pascal Spincemaille1, Thanh Dang Nguyen1, Martin Prince1, Yi Wang1
1Weill Medical College of Cornell University, New York, USA
Free breathing self-gated CINE acquisitions mostly rely on retrospective gating. A better suppression of motion artifacts and higher scanning efficiency can be achieved using prospective data acquisition gating. This abstract proposes the use of a commonly used real time filtering technique called the Kalman filter for processing noisy navigator data in real time. The Kalman filter adaptively estimates motion and suppresses measurement noise using Bayesian statistics and a motion model. Its ability to reduce noise and separate cardiac and respiratory components is studied in simulations, in-vivo data and in a free-breathing prospectively self-gated CINE SSFP acquisition of the heart.
Cardiac Gating Free of Interference with
Electro-Magnetic Fields at 1.5T, 3.0T and 7.0T
Tobias Frauenrath1, 2, Sebastian Kozerke2, Peter Boesiger2, Thoralf Niendorf1
1RWTH Aachen University, Aachen, Germany; 2University and ETH Zurich, Switzerland
In clinical MRI cardiac motion is commonly dealt with using ECG based synchronization. ECG is prone to interference with electromagnetic fields and to magneto-hydrodynamic effects, in particular at (ultra)high magnetic field strengths. For all these reasons, a non-invasive, fully MR compatible cardiac monitoring and gating approach which presents immunity to electro-magnetic field interferences is conceptually appealing. For this purpose a cardiac monitoring and gating device that employs acoustic signals was proposed. The chief aim of the current study is to explore the suitability of acoustic cardiac gating (ACG) for (ultra)high magnetic field strengths.
A Novel Technique Used to Detect Swallowing in Volume
Selective TSE for Carotid Artery Wall Imaging
Cheuk Fan Chan1, Raymond L. Hughes1, Peter Gatehouse1, Dudley J. Pennell2, David Firmin2
1Royal Brompton Hospital, London, UK; 2Royal Brompton Hospital, UK
Atherosclerotic carotid artery disease and the associated sequelae are the commonest cause of morbidity and mortality from cerebrovascular events in the Western world. Various MRI techniques have been established to image the vessel wall and to characterize plaque. Significant work to reduce scan times without compromising image quality has been undertaken. Artifacts associated with swallowing and heart rate variability lead to blurring and a reduction in vessel wall clarity. Using a novel anatomically positioned device linked with a k-space data rejection algorithm, we can demonstrate the improvement in the image quality.
Prospective Motion Correction Via Real-Time Active
Marker Tracking: An Image Quality Assessment
Melvyn Boon King Ooi1, Sascha Krueger2, William Thomas3, S. V. Swaminathan4, Truman R. Brown1,3
1Dept of Biomedical Engineering, Columbia University, New York City, USA; 2Philips Research, Hamburg, Germany; 3Dept of Radiology, Columbia University, New York City, USA; 4Philips Medical Systems, Cleveland, Ohio, USA
Subject motion is a fundamental problem in MRI. We present here continuing work on prospective motion correction using micro RF-coils for fast motion tracking, followed by real-time scan geometry update. In particular, this work provides evidence, in quantitative metrics, that highlights the potential improvements in image quality allowed by this technique.
Velocity-Compensated DENSE MRI
Xiaodong Zhong1, Florent Sureau1, Frederick H. Epstein1
1University of Virginia, Charlottesville, Virginia , USA
In DENSE, tissue displacement during the time between displacement encoding and the excitation RF pulse is intended to be measured. However, phase shifts unrelated to the desired displacement-induced shift can occur during the displacement-encoding period and the readout period due to tissue velocity. The purpose of this study was to investigate the errors caused by tissue velocity during these two periods on DENSE displacement estimates, and to show that these errors can be eliminated using velocity-compensated (first moment nulled) gradient waveforms.
Reduction of Flow Artifacts in Balanced SSFP Imaging
J. Andrew Derbyshire1, Michael A. Guttman2, Robert J. Lederman2, Elliot R. McVeigh2
1National Institutes of Health, DHHS, Bethesda, Maryland, USA; 2NHLBI, National Institutes of Health, DHHS, Bethesda, Maryland, USA
Balanced SSFP imaging often suffers from severe artifacts due to (e.g. blood) spins that flow from one spectral band into an adjacent phase-opposed band. The flowing spins yield oscillating transient signals for the following several hundred TRs and hence imaging artifacts. The S5FP sequence provides balanced SSFP-like contrast for on-resonance spins, but destroys magnetization depending on the phase of the magnetization at TE = TR/2. Here we demonstrate that S5FP is an effective, robust and efficient method to suppress flow artifacts in balanced SSFP imaging.