MR Elastography
Thursday 23 April 2009
Room 315 16:00-18:00


Richard L. Ehman and Donald B. Plewes

16:00 709. Validity of a 2-D Wave Field Model in MR Elastography of the Liver
    Meng Yin1, Kevin J. Glaser1, Jayant A. Talwalkar2, Armando Manduca1, Richard L. Ehman1
Department of Radiology, Mayo Clinic, Rochester, MN, USA; 2Division of Gastroenterology & Hepatology, Mayo Clinic, Rochester, MN, USA
    One advantage of liver MRE over biopsy or ultrasound-based transient elastography is its ability to reduce sampling error by measuring liver stiffness in multiple areas of the liver. While full 7-D wave imaging offers valid measurement of stiffness throughout the liver, the 2-D approach may also provide valid results in a significant part of the volume, with a substantially reduced imaging time. This investigation compared these two approaches, validated the key element of the protocol that makes this possible – the optimized acoustic driver system can provide a wave propagation geometry that is suitable for reliable 2-D wave imaging.
16:12 710. Vitreal Viscoelasticity Revealed by Motion-Encoded MRI
    Marco Piccirelli1,2, Oliver Bergamin2, Klara Landau2, Peter Boesiger1, Roger Luechinger1
Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 2Department of Ophthalmology, University Hospital, Zurich, Switzerland
    The vitreous shear stress can damage the retina and induce visual loss. Up to now, the vitreous viscoelasticity has only been measured ex-vivo. However, the intravitreal membranes may impact on the shear stress. We determined the vitreous deformation properties in-vivo with intact intravitreal membranes, using peak-combination HARP on CSPAMM images. The vitreous viscoelasticity was determined by fitting the deformation with an analytic model. We were able to split the subjects into 4 groups: gel-like, intermediate, liquefied, and polyphasic vitreous. Our results contrasted with ex-vivo data, which do not include the intravitreal membranes.
16:24 711. Application of DENSE MR-Elastography to the Human Heart: First in Vivo Results
    Benjamin Robert1, Ralph Sinkus1, Jean-Luc Gennisson1, Mathias Fink1
Laboratoire Ondes et Acoustique, Ecole Supérieure de Physique et Chimie Industrielles, Paris, France
    Cardiac MR-Elastography presents several challenges due to short T2* and periodic myocardium activity. Moreover, low frequency elastic waves should be used as the heart is located deeply within the chest. Thus, conventional MRE has failed to be implemented to myocardium. A new MRE sequence has been derived from DENSE sequence, and it is applied to two healthy volunteers. In vivo cardiac feasibility is shown, and elastograms are estimated for four different heart phases during diastole for both volunteers. The shear modulus maps are characterized by an increase during diastole as the heart wall becomes stiffer during the ventricle blood filling.
16:36 712. Auto-Elastography of the Brain
    Sha Zhao1, Alan Jackson1, Geoffrey J. Parker1
ISBE, University of Manchester, Manchester, England, UK
    We present our findings of using a phase contrast imaging technique to detect brain tissue’s motion induced by blood and CSF pulsation. We present methods to enable the calculation of elasticity from this motion, which allows elastography with no external driving device. We demonstrate that our measurements are compatible with previous measurements of shear modulus in the brain.
16:48 713. Anomalous Shear Wave Propagation Reveals Micro-Architectural Properties - Potential Implications for Diagnostic Imaging
    Ralph Sinkus1, Benoit Larrat1, Najat Salameh2, Katja Siegmann3, Bernard Van Beers2, Mathias Fink1
Laboratoire Ondes et Acoustique, ESPCI, Paris, France; 2Radiodiagnostic Unit, Université Catholique de Louvain, Brussels, Belgium; 3Abteilung Radiologische Diagnostik, Universitätsklinikum Tübingen, Tübingen, Germany
    Anomalous shear wave propagation reveals micro-architectural properties of underlying hard scattering structures. This is shown via simulations, phantom experiments, in-vivo liver fibrosis and breast cancer data. Thereby, unique information about the vascular architecture of tumours at the clinical imaging scale are accessible.
17:00 714. High Resolution MR-Elastography Mouse Brain Study: Towards a Mechanical Atlas
    Elsa Diguet1, Elijah van Houten2, Michael Green3, Ralph Sinkus1
Laboratoire Ondes et Acoustique, ESPCI, Paris, France; 2University of Canterbury, Christchurch, New Zealand; 3Prince of Wales Medical Research Institute, Sydney, Australia
    High resolution MR-elastography is applied to image the mechanical properties of mice brain in particular the corpus callosum at 1000Hz. A reproducibility study shows that the obtained values for the complex shear modulus are stable (Gd:7%, Gl:25%) and that also other myelinated structures are well visible like the optic tract or the superior cerebellar peduncle.
17:12 715. A Protocol for Assessing Hepatic Fibrosis in Iron-Overloaded Liver Tissue with MR Elastography
    David W. Stanley1, Meng Yin2, Kevin J. Glaser2, Richard L. Ehman2
GE Healthcare, Proctor, MN, USA; 2Department of Radiology, Mayo Clinic, Rochester, MN, USA
    Patients that have had high iron concentration in their liver tissue, which leads to severely, shortened T2/T2*, can be problematic at 3.0T because it produces poor MR signal in the liver and MRE liver stiffness measurements may not be valid due to the extremely low SNR. We explored the relationship between the SNR and the motion sensitivity of MRE by varying the time duration of the motion-encoding gradients (MEG) in the MRE pulse sequence. A modified MRE protocol with broader receive bandwidth and fractional period MEG was developed for use in patients with iron-overloaded liver tissue.
17:24 716. TREMR: Table-Resonance Elastography with MR
    Daniel Gallichan1, Matthew D. Robson2, Andreas J. Bartsch3, Karla L. Miller1
FMRIB Centre, University of Oxford, Oxford, Oxon, UK; 2OCMR, University of Oxford; 3Neuroradiology, University of Würzburg
    Low-frequency gradient switching leads to substantial vibration of the patient table. Here we successfully demonstrate that these vibrations can be used to image the propagation of vibrational shear waves through the brain. This suggests a method allowing MR Elastography to be performed without the need for purpose-built hardware to generate the vibrations.
17:36 717. MR Acoustic Radiation Force Imaging: In Vivo Comparison to Ultrasound Motion Tracking
    Yuexi Huang1, Laura Curiel2, Aleksandra Kukic1, Rajiv Chopra1, Kullervo Hynynen1,3
Sunnybrook Health Sciences Centre, Toronto, ON, Canada; 2Thunder Bay Regional Research Institute, Thunder Bay, ON, Canada; 3Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
    MR acoustic radiation force imaging (MR-ARFI) was applied in vivo on rabbit thigh muscle simultaneously with real-time ultrasound motion tracking, by which time-resolved displacement values during the MR measurement were measured. Square-modulated focused ultrasound pulses at 50 Hz were applied at 25W acoustical power with 1% duty cycle during the measurements. Time-averaged results from the two modalities were compared. Results showed general agreement between MR-ARFI and the calculated ultrasound data.
17:48 718. Proper Orthogonal Decomposition for Improved Assessment of Brain MR Elastography: Initial Results
    Curtis L. Johnson1, Dimitrios C. Karampinos1,2, Danchin Chen1, Bradley P. Sutton2,3, William C. Olivero2,4, John G. Georgiadis1,2
Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, IL, USA; 2Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA; 3Bioengineering Department, University of Illinois at Urbana-Champaign, Urbana, IL, USA; 4Department of Neurosurgery, University of Illinois at Urbana-Champaign, Urbana, IL, USA
    The Proper Orthogonal Decomposition (POD) method is proposed to extract shear wave modes from human brain Magnetic Resonance Elastography (MRE) data sets. The POD method allows for mode extraction from a dynamic system regardless of linearity. This is an improvement over current MRE post-processing techniques which assume that the harmonically actuated brain is a linear system, possibly leading to variations in results between studies. It is shown that POD can be used to extract dynamic modes in the human brain during MRE experiments, and can be used to improve data analysis and create a simple, dynamic model of the brain.