title: A Surrogate Measure of Cortical Bone Matrix Density by Long T2 -Suppressed MRI.
abstract: Magnetic resonance has the potential to image and quantify two pools of water within bone: free water within the Haversian pore system (transverse relaxation time, T2 > 1 ms), and water hydrogen-bonded to matrix collagen (T2 ∼ 300 to 400 μs). Although total bone water concentration quantified by MRI has been shown to scale with porosity, greater insight into bone matrix density and porosity may be gained by relaxation-based separation of bound and pore water fractions. The objective of this study was to evaluate a recently developed surrogate measurement for matrix density, single adiabatic inversion recovery (SIR) zero echo-time (ZTE) MRI, in human bone. Specimens of tibial cortical bone from 15 donors (aged 27 to 97 years; 8 female and 7 male) were examined at 9.4T field strength using two methods: (1) (1)H ZTE MRI, to capture total (1)H signal, and (2) (1)H SIR-ZTE MRI, to selectively image matrix-associated (1)H signal. Total water, bone matrix, and bone mineral densities were also quantified gravimetrically, and porosity was measured by micro-CT. ZTE apparent total water (1)H concentration was 32.7 ± 3.2 M (range 28.5 to 40.3 M), and was correlated positively with porosity (R(2) = 0.80) and negatively with matrix and mineral densities (R(2) =  0.90 and 0.82, respectively). SIR-ZTE apparent bound water (1)H concentration was 32.9 ± 3.9 M (range 24.4 to 39.8 M), and its correlations were opposite to those of apparent total water: negative with porosity (R(2) = 0.73) and positive with matrix density (R(2) = 0.74) and mineral density (R(2) = 0.72). Porosity was strongly correlated with gravimetric matrix density (R(2) = 0.91, negative) and total water density (R(2) = 0.92, positive). The strong correlations of SIR-ZTE-derived apparent bound water (1)H concentration with ground-truth measurements suggest that this quantitative solid-state MRI method provides a nondestructive surrogate measure of bone matrix density.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Alan C
authors.initials: AC
authors.lastname: Seifert
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.affiliation: NMR Core Facility, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Wehrli
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001857:Bone Matrix / Q000033:anatomy & histology*; D001842:Bone and Bones / Q000033:anatomy & histology*; D003094:Collagen / Q000737:chemistry; D005260:Female; D006801:Humans; D006860:Hydrogen Bonding; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016062:Porosity; D011522:Protons; D013818:Thermogravimetry; D013977:Tibia / Q000033:anatomy & histology; D014867:Water / Q000737:chemistry; D055114:X-Ray Microtomography
chemical_list: D011522:Protons; D014867:Water; D003094:Collagen
keywords: BONE DENSITY; BONE POROSITY; BONE WATER; MRI; ZERO ECHO-TIME (ZTE)