title: Overhauser-enhanced magnetic resonance elastography.
abstract: Magnetic resonance elastography (MRE) is a powerful technique to assess the mechanical properties of living tissue. However, it suffers from reduced sensitivity in regions with short T2 and T2 * such as in tissue with high concentrations of paramagnetic iron, or in regions surrounding implanted devices. In this work, we exploit the longer T2 * attainable at ultra-low magnetic fields in combination with Overhauser dynamic nuclear polarization (DNP) to enable rapid MRE at 0.0065 T. A 3D balanced steady-state free precession based MRE sequence with undersampling and fractional encoding was implemented on a 0.0065 T MRI scanner. A custom-built RF coil for DNP and a programmable vibration system for elastography were developed. Displacement fields and stiffness maps were reconstructed from data recorded in a polyvinyl alcohol gel phantom loaded with stable nitroxide radicals. A DNP enhancement of 25 was achieved during the MRE sequence, allowing the acquisition of 3D Overhauser-enhanced MRE (OMRE) images with (1.5 × 2.7 × 9) mm(3) resolution over eight temporal steps and 11 slices in 6 minutes. In conclusion, OMRE at ultra-low magnetic field can be used to detect mechanical waves over short acquisition times. This new modality shows promise to broaden the scope of conventional MRE applications, and may extend the utility of low-cost, portable MRI systems to detect elasticity changes in patients with implanted devices or iron overload.
authors.affiliation: Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Radiology, Harvard Medical School, Boston, MA, USA.|Department of Physics, Harvard University, Cambridge, MA, USA.|Institute of Physics of Biological Systems, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Najat
authors.initials: N
authors.lastname: Salameh
authors.affiliation: Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Radiology, Harvard Medical School, Boston, MA, USA.|Department of Physics, Harvard University, Cambridge, MA, USA.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Sarracanie
authors.affiliation: Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Physics, Harvard University, Cambridge, MA, USA.
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Armstrong
authors.affiliation: Department of Radiology, A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.|Department of Radiology, Harvard Medical School, Boston, MA, USA.|Department of Physics, Harvard University, Cambridge, MA, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Rosen
authors.affiliation: Institute of Physics of Biological Systems, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Comment
mesh_terms: D003198:Computer Simulation; D054459:Elasticity Imaging Techniques / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
keywords: Electron Spin Resonance (ESR); MR Elastography (MRE); Overhauler MRI; iron overload; magnetic susceptibility; ultra-low magnetic field