title: Solid-State Quantitative (1)H and (31)P MRI of Cortical Bone in Humans.
abstract: Magnetic resonance imaging (MRI) plays a pivotal role for assessment of the musculoskeletal system. It is currently the clinical modality of choice for evaluation of soft tissues including cartilage, ligaments, tendons, muscle, and bone marrow. By comparison, the study of calcified tissue by MRI is still in its infancy. In this article, we review the potential of the modality for assessment of cortical bone properties known to be affected in degenerative bone disease, with focus on parameters related to matrix and mineral densities, and porosity, by means of emerging solid-state (1)H and (31)P MRI techniques. In contrast to soft tissues, the MRI signal in calcified tissues has very short lifetime, on the order of 100 μs to a few milliseconds, demanding customized imaging approaches that allow capture of the signal almost immediately after excitation. The technologies described are suited for quantitatively imaging human cortical bone in specimens as well as in vivo in patients on standard clinical imagers, yielding either concentrations in absolute units when measured against a reference standard, or more simply, in the form of surrogate biomarkers. The two major water fractions in cortical bone are those of collagen-bound and pore water occurring at an approximately 3:1 ratio. Collagen-bound water density provides a direct quantitative measure of osteoid density. While at an earlier stage of development, quantification of mineral phosphorus by (31)P MRI yields mineral density and, together with knowledge of matrix density, should allow quantification of the degree of bone mineralization.
authors.affiliation: Laboratory for Structural, Physiologic, and Functional Imaging, Department of Radiology, University of Pennsylvania Medical Center, MRI Education Center, 1st Floor Founders, 3400 Spruce St., Philadelphia, PA, 19104, USA.
authors.forename: Alan C
authors.initials: AC
authors.lastname: Seifert
authors.affiliation: Laboratory for Structural, Physiologic, and Functional Imaging, Department of Radiology, University of Pennsylvania Medical Center, MRI Education Center, 1st Floor Founders, 3400 Spruce St., Philadelphia, PA, 19104, USA. wehrli@mail.med.upenn.edu.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D015519:Bone Density; D001857:Bone Matrix / Q000000981:diagnostic imaging*; D001842:Bone and Bones / Q000000981:diagnostic imaging; D002113:Calcification, Physiologic; D003094:Collagen; D000071538:Cortical Bone / Q000000981:diagnostic imaging*; D005109:Extracellular Matrix; D006801:Humans; D006859:Hydrogen; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010759:Phosphorus Isotopes; D016062:Porosity; D014867:Water
chemical_list: D010759:Phosphorus Isotopes; D014867:Water; D006859:Hydrogen; D003094:Collagen
keywords: Bone mineral density; Bone water; Cortical bone; Solid-state MRI; UTE; ZTE