title: Ultrashort echo time magnetization transfer (UTE-MT) imaging of cortical bone.
abstract: Magnetization transfer (MT) imaging is one way to indirectly assess pools of protons with fast transverse relaxation. However, conventional MT imaging sequences are not applicable to short T2 tissues such as cortical bone. Ultrashort echo time (UTE) sequences with TE values as low as 8 µs can detect signals from different water components in cortical bone. In this study we aim to evaluate two-dimensional UTE-MT imaging of cortical bone and its application in assessing cortical bone porosity as measured by micro-computed tomography (μCT) and biomechanical properties. In total, 38 human cadaveric distal femur and proximal tibia bones were sectioned to produce 122 rectangular pieces of cortical bone for quantitative UTE-MT MR imaging, μCT, and biomechanical testing. Off-resonance saturation ratios (OSRs) with a series of MT pulse frequency offsets (Δf) were calculated and compared with porosity assessed with μCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation and linear regression. A moderately strong negative correlation was observed between OSR and μCT porosity (R(2)  = 0.46-0.51), while a moderate positive correlation was observed between OSR and yield stress (R(2)  = 0.25-0.30) and failure stress (R(2)  = 0.31-0.35), and a weak positive correlation (R(2)  = 0.09-0.12) between OSR and Young's modulus at all off-resonance saturation frequencies. OSR determined with the UTE-MT sequence provides quantitative information on cortical bone and is sensitive to μCT porosity and biomechanical function.
authors.affiliation: Department of Radiology, VA San Diego Healthcare System, La Jolla, CA, USA.|Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Eric Y
authors.initials: EY
authors.lastname: Chang
authors.affiliation: Department of Radiology, VA San Diego Healthcare System, La Jolla, CA, USA.
authors.forename: Won C
authors.initials: WC
authors.lastname: Bae
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Hongda
authors.initials: H
authors.lastname: Shao
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Reni
authors.initials: R
authors.lastname: Biswas
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Shihong
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.|Department of Orthopedics, Peking Union Medical College Hospital, Beijing, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.affiliation: Shiley Center for Orthopaedic Research and Education, Scripps Clinic, La Jolla, CA, USA.
authors.forename: Shantanu
authors.initials: S
authors.lastname: Patil
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Healey
authors.affiliation: Shiley Center for Orthopaedic Research and Education, Scripps Clinic, La Jolla, CA, USA.
authors.forename: Darryl D
authors.initials: DD
authors.lastname: D'Lima
authors.affiliation: Department of Radiology, VA San Diego Healthcare System, La Jolla, CA, USA.|Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Christine B
authors.initials: CB
authors.lastname: Chung
authors.affiliation: Department of Radiology, University of California, San Diego, CA, USA.
authors.forename: Jiang
authors.initials: J
authors.lastname: Du
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000502:physiology*; D002102:Cadaver; D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D016062:Porosity; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology
keywords: UTE; cortical bone; magnetization transfer; off-resonance saturation ratio; porosity