title: Whole brain mapping of water pools and molecular dynamics with rotating frame MR relaxation using gradient modulated low-power adiabatic pulses.
abstract: Nuclear magnetic resonance (NMR) relaxation in the rotating frame is sensitive to molecular dynamics on the time scale of water molecules interacting with macromolecules or supramolecular complexes, such as proteins, myelin and cell membranes. Hence, longitudinal (T1ρ) and transverse (T2ρ) relaxation in the rotating frame may have a great potential to probe the macromolecular fraction of tissues. This stimulated a large interest in using this MR contrast to image brain under healthy and disease conditions. However, experimental challenges related to the use of intense radiofrequency irradiation have limited the widespread use of T1ρ and T2ρ imaging. Here, we present methodological development to acquire 3D high-resolution or 2D (multi-)slice selective T1ρ and T2ρ maps of the entire human brain within short acquisition times. These improvements are based on a class of gradient modulated adiabatic pulses that reduce the power deposition, provide slice selection, and mitigate artifacts resulting from inhomogeneities of B1 and B0 magnetic fields. Based on an analytical model of the T1ρ and T2ρ relaxation we compute the maps of macromolecular bound water fraction, correlation and exchange time constants as quantitative biomarkers informative of tissue macromolecular content. Results obtained from simulations, phantoms and five healthy subjects are included.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA. Electronic address: ovidiu@nmr.mgh.harvard.edu.
authors.forename: Ovidiu C
authors.initials: OC
authors.lastname: Andronesi
authors.affiliation: Siemens Medical Solutions USA Inc, Charlestown, MA 02129, USA.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Bhat
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Reuter
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Shreya
authors.initials: S
authors.lastname: Mukherjee
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Caravan
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Rosen
mesh_terms: D000328:Adult; D001923:Brain Chemistry; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D008297:Male; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water
keywords: Bound water fraction; Correlation time; Exchange time; Macromolecular content; Neurodegeneration; Rotating frame relaxation (T1ρ, T2ρ)