|Quantitative Flow Imaging|
Assessment of Stroke Volume Variability Using
Real-Time Spiral Phase Contrast
Joao Luiz Azevedo de Carvalho1, Hervaldo Sampaio Carvalho2, Krishna S. Nayak1
1University of Southern California, Los Angeles, California , USA; 2University of Brasilia, Brasilia, Brazil
Stroke volume variability provides information about the activity of the autonomic nervous system, connecting heart rate variability to blood pressure and venous return variabilities. There is currently no non-invasive gold-standard for measuring stroke volume. Recent MR methods can measure cardiac output by integrating flow volume through several cardiac cycles. We propose a method that is capable of measuring changes in stroke volume on a beat-to-beat basis, using real-time spiral phase contrast. We present and discuss measured dynamic changes in stroke volume during stimuli such as the Valsalva maneuver, handgrip, facial cooling, mental stress and cold pressor.
Real-Time and Cardiac Gated CINE MR Doppler
Juan Manuel Santos1, Adam B. Kerr1, Daeho Lee1, Michael V. McConnell1, Phillip C. Yang1, Bob S. Hu2, John M. Pauly1
1Stanford University, Stanford, USA; 2Palo Alto Medical Foundation, Palo Alto, USA
The examination of valvular heart disease includes the assessment of valvular morphology, cardiac output, intracardiac pressures, ventricular volume and volume regurgitations. Magnetic resonance imaging (MRI) is potentially the most appropriate technique for addressing all of these areas in a single examination. We have previously implemented an MRI subsystem that seamlessly integrates most of the capabilities needed for a comprehensive valve evaluation. In this work, we have expanded this system to include a cardiac gated CINE MR Doppler sequence to improve the resolution and velocity range of our previously demonstrated Real-Time MR Doppler sequence.
Reference-Less Flow Measurements Using
Jon-Fredrik Nielsen1, Krishna S. Nayak1
1University of Southern California, Los Angeles, California , USA
Phase-contrast (PC) MRI is an established flow quantitation technique, but suffers from limited spatio-temporal resolution, and inferior SNR compared to balanced SSFP sequences. Recently, several groups have proposed PC-MRI methods based on SSFP, which achieve accurate flow quantitation with high SNR efficiency. However, the total acquisition time for any phase-contrast-based method is intrinsically high, since one or more separate phase reference scans must be acquired. We propose a flow quantitation approach that exploits the intrinsic refocusing property of SSFP, to achieve 50% reductions in scan time.
Accelerated Phase-Contrast MR Imaging: Comparison of
SENSE, K-T BLAST and Doppler Ultrasound for Velocity and Flow
Measurements of the Aorta
Andreas Stadlbauer1, Wilma van der Riet2, Sebastian Globits3, Gerard Crelier4, Erich Salomonowitz1
1Landesklinikum St.Poelten, St. Poelten, Austria; 2European MRI Consultancy (EMRIC), Strasbourg, France; 3Landesklinikum St. Poelten, St. Poelten, Austria; 4GyroTools, Zurich, Switzerland
To evaluate differences in aortic velocity and flow measurements between accelerated phase-contrast MRI using SENSE and k-t BLAST, and were correlated to continuous wave (CW) Doppler. 2D PC-MRI was performed using SENSE (R=2) and k-t BLAST (2-, 4-, 6-, and 8-fold). Peak and mean velocity, and stroke volume of accelerated PC-MRIs were compared. Strong correlations between SENSE and k-t BLAST were found for all parameters. Significant differences between SENSE and 4-, 6-, and 8-fold k-t BLAST were found in peak velocity and stroke volume. Peak velocities was underestimated by PC-MRI but correlated significant with CW-Doppler.
Improved Velocity-To-Noise Ratio in Time-Resolved 3D
Blood Flow Measurements for Cardiac Imaging
Jochen von Spiczak1, Robert Manka1, Gérard Crelier1, Peter Boesiger1, Sebastian Kozerke1
1University and ETH Zurich, Zurich, Switzerland
Time-resolved phase-contrast imaging permits the assessment of volumetric, multi-directional blood flow velocities. The objective of this work was to improve the velocity-to-noise ratio by lowering the encoding velocity in conjunction with an automatic phase unwrapping algorithm suited for time-resolved 3D blood flow measurements. The gain in VNR was used to compensate for SNR loss in accelerated scans using parallel imaging and concurrently increase spatial resolution. Comparing relative VNR of the normal and accelerated acquisitions resulted in a factor close to the theoretical prediction. A patient with a dilated ascending aorta was scanned demonstrating the feasibility of such technique.
MRI Determination of Pulse Wave Velocity in the
Christopher J. Hardy1, Luca Marinelli1, Daniel J. Blezek1, Robert D. Darrow1
1GE Global Research, Niskayuna, New York, USA
Fourier-velocity-encoded M-mode MRI provides a fast, non-invasive measure of pulse wave velocity, and thus arterial distensibility. In this technique, a movie of blood velocity distributions is generated, in which the velocity wave can be seen propogating along the artery. Several improvements have been made to this technique to allow its use in shorter segments of smaller vessels, such as the carotid arteries. A new analysis method has been developed for more accurate semi-automated calculation of PWV. Pencil excitation pulses employing more spiral turns and using stronger gradients have also been developed to reduce pencil diameters to 5 mm.
Aortic Pulse Wave Velocity Assessed with
Velocity-Encoded MRI: Validation with Catheterization and Clinical
Jos J.M. Westenberg1, Heynric B. Grotenhuis1, Paul Steendijk1, Dennis Hendriksen1, Theodorus A.M. Kaandorp1, Rob J. van der Geest1, J. W. Jukema1, Jeroen J. Bax1, Johan H.C. Reiber1, Albert de Roos1
1Leiden University Medical Center, Leiden, Netherlands
Aortic Pulse Wave Velocity (PWV), a surrogate marker for arterial wall compliance, is assessed non-invasively with Velocity-Encoded MRI and compared with invasive pressure measurements during catheterization. Reproducibility as well as physiological variation in PWV is tested and clinically applied to define cut-off values for discriminating coronary disease.
Hemodynamics and Wall Shear Stress in the Pulmonary
Arteries of Hypertension Patients Using Phase Contrast MRI
Alex J. Barker1, Craig Lanning2, Robin Shandas, 12
1University of Colorado, Boulder, Colorado , USA; 2The Children's Hospital, Denver, Colorado , USA
Pulmonary arterial hypertension (PAH) is an important determinant of morbidity and mortality in children with congenital heart disease. In order to further understand this complex disease, and, since hemodynamic factors are known pathophysiological stimuli in the production of molecules that alter vascular tone and matrix properties, this study attempted to quantify these effects in the proximal left, right and main pulmonary arteries (LPA, RPA, & MPA) of control and hypertensive patients using phase-contrast magnetic resonance imaging (PC-MRI). Preliminary results show that PAH patients demonstrate a marked difference in both their flow pulse and WSS waveforms when compared to normotensive patients.
Temporal Stability of the Background Velocity Error
Supports Automated Correction of Flow Measurements
Peter D. Gatehouse1, Ajmal Nafisa, Philip J. Kilner, David N. Firmin
1Royal Brompton Hospital, London, UK
Background errors even smaller than 1% of the VENC can seriously affect measurements of regurgitant fraction and shunt flow. This abstract investigates the feasibility of using stored background error corrections acquired once in a set of relevant planes and sequence parameters. This approach assumes that the background offset error is stable with time. In the absence of any published data on this stability, we tested it over 40 days and found that the background is stable enough to support this approach.
Magnetic Field Monitoring for Improved Phase Contrast
Florian Wiesinger1, Silke Maria Lechner1, 2, Pekka Sipilae1, 2, Thomas K. Foo3
1GE Global Research, Munich, Germany; 2Munich University of Technology, Munich, Germany; 3GE Global Research, Niskayuna, New York, USAPhase contrast (PC) based flow quantification is prone to magnetic field imperfections caused by Eddy currents and concomitant fields. This problem is known to result in inaccurate quantification of volume flow rates, with the potential implication of misleading diagnosis. In this work, a novel correction technique is presented based on magnetic field monitoring (MFM). Dedicated magnetic field sensors are utilized to measure the actual magnetic fields during the execution of the pulse sequence. Phantom results indicate a significant improvement of PC-based flow quantification using MFM.