title: Magnetization transfer imaging of cortical bone in vivo using a zero echo time sequence in mice at 4.7 T: a feasibility study.
abstract: OBJECTIVE
  To investigate the feasibility of magnetization transfer (MT) imaging in mice in vivo for the assessment of cortical bone.
  
  
  METHODS
  MT-zero echo time data were acquired at 4.7 T in six mice using MT preparation pulses with two different flip angles (FAs) and a series of ten different off-resonance frequencies (500-15000 Hz). Regions of interest were drawn at multiple levels of the femoral cortical bone. The MT ratio (MTR) was computed for each combination of FAs and off-resonance frequencies. T1 measurements were used to estimate the direct saturation (DS) using a Bloch equation simulation. Estimation of the absorption line width of cortical bone from T2* measurements was also performed.
  
  
  RESULTS
  MTR values were higher using 3000° FA than 1000° FA. MTR values decreased toward higher off-resonance frequencies. Maximum mean MTR ± standard deviation (SD) of 58.57 ± 5.22 (range 50.44-70.61) was measured with a preparation pulse of 3000° and off-resonance frequency of 500 Hz. Maximum "true" MT effect was estimated at around 2-3 and 5 kHz, respectively, for 1000° and 3000° FA. Mean full width at half maximum ± SD of 577 ± 91 Hz was calculated for the absorption spectral line of the cortical bone.
  
  
  CONCLUSIONS
  MT imaging can be used for the assessment of cortical bone in mice in vivo. DS effects are negligible using preparation pulses with off-resonance frequencies greater than 3 kHz.
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland. magda.marcon@usz.ch.
authors.forename: Magda
authors.identifier: http://orcid.org/0000-0003-3923-8115
authors.initials: M
authors.lastname: Marcon
authors.affiliation: Institute for Biomedical Engineering, University of Zurich and Swiss Federal Institute for Technology, Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Weiger
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland.|Department of Urology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Keller
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland.
authors.forename: Moritz C
authors.initials: MC
authors.lastname: Wurnig
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Eberhardt
authors.affiliation: Department of Urology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Eberli
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Boss
mesh_terms: D000465:Algorithms; D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000503:physiopathology; D003198:Computer Simulation; D000071538:Cortical Bone / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005240:Feasibility Studies; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D051379:Mice; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D057170:Translational Research, Biomedical
keywords: Bone; Magnetization transfer imaging; Translational medical research