title: Evaluation of bound and pore water in cortical bone using ultrashort-TE MRI.
abstract: Bone water exists in different states with the majority bound to the organic matrix and to mineral, and a smaller fraction in 'free' form in the pores of cortical bone. In this study, we aimed to develop and evaluate ultrashort-TE (UTE) MRI techniques for the assessment of T2*, T1 and concentration of collagen-bound and pore water in cortical bone using a 3-T clinical whole-body scanner. UTE MRI, together with an isotope study using tritiated and distilled water (THO-H2O) exchange, as well as gravimetric analysis, were performed on ten sectioned bovine bone samples. In addition, 32 human cortical bone samples were prepared for comparison between the pore water concentration measured with UTE MRI and the cortical porosity derived from micro-computed tomography (μCT). A short T2* of 0.27 ± 0.03 ms and T1 of 116 ± 6 ms were observed for collagen-bound water in bovine bone. A longer T2* of 1.84 ± 0.52 ms and T1 of 527 ± 28 ms were observed for pore water in bovine bone. UTE MRI measurements showed a pore water concentration of 4.7-5.3% by volume and collagen-bound water concentration of 15.7-17.9% in bovine bone. THO-H2O exchange studies showed a pore water concentration of 5.9 ± 0.6% and collagen-bound water concentration of 18.1 ± 2.1% in bovine bone. Gravimetric analysis showed a pore water concentration of 6.3 ± 0.8% and collagen-bound water concentration of 19.2 ± 3.6% in bovine bone. A mineral water concentration of 9.5 ± 0.6% was derived in bovine bone with the THO-H2O exchange study. UTE-measured pore water concentration is highly correlated (R(2) = 0.72, p < 0.0001) with μCT porosity in the human cortical bone study. Both bovine and human bone studies suggest that UTE sequences could reliably measure collagen-bound and pore water concentration in cortical bone using a clinical scanner.
authors.affiliation: Department of Orthopedics, Peking Union Medical College, Beijing, China.|Department of Radiology, University of California, San Diego, CA.
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.affiliation: Shiley Center for Orthopedic Research and Education at Scripps Clinic, La Jolla, CA.
authors.forename: Shawn P
authors.initials: SP
authors.lastname: Grogan
authors.affiliation: Department of Radiology, University of California, San Diego, CA.
authors.forename: Hongda
authors.initials: H
authors.lastname: Shao
authors.affiliation: Shiley Center for Orthopedic Research and Education at Scripps Clinic, La Jolla, CA.
authors.forename: Darryl
authors.initials: D
authors.lastname: D'Lima
authors.affiliation: Department of Radiology, University of California, San Diego, CA.
authors.forename: Graeme M
authors.initials: GM
authors.lastname: Bydder
authors.affiliation: Department of Orthopedics, Peking Union Medical College, Beijing, China.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Department of Radiology, University of California, San Diego, CA.
authors.forename: Jiang
authors.initials: J
authors.lastname: Du
mesh_terms: D000818:Animals; D001834:Body Water / Q000378:metabolism*; D002417:Cattle; D003094:Collagen / Q000378:metabolism*; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000378:metabolism*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D016062:Porosity; D011485:Protein Binding; D011859:Radiography; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D003094:Collagen
keywords: UTE; bone; bound water; organic matrix; pore water