title: Improved cortical bone specificity in UTE MR Imaging.
abstract: Methods for direct visualization of compact bone using MRI have application in several "MR-informed" technologies, such as MR-guided focused ultrasound, MR-PET reconstruction and MR-guided radiation therapy. The specificity of bone imaging can be improved by manipulating image sensitivity to Bloch relaxation phenomena, facilitating distinction of bone from other tissues detected by MRI.
  
  
  
  From Bloch equation dynamics, excitation pulses suitable for creating specific sensitivity to short-T2magnetization from cortical bone are identified. These pulses are used with UTE subtraction demonstrate feasibility of MR imaging of compact bone with positive contrast.
  
  
  
  MR images of bone structures are acquired with contrast similar to that observed in x-ray CT images. Through comparison of MR signal intensities with CT Hounsfield units of the skull, the similarity of contrast is quantified. The MR technique is also demonstrated in other regions of the body that are relevant for interventional procedures, such as the shoulder, pelvis and leg.
  
  
  
  Matching RF excitation pulses to relaxation rates improves the specificity to bone of short-T2contrast. It is demonstrated with a UTE sequence to acquire images of cortical bone with positive contrast, and the contrast is verified by comparison with x-ray CT. Magn Reson Med 77:684-695, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Ethan M
authors.initials: EM
authors.lastname: Johnson
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Urvi
authors.initials: U
authors.lastname: Vyas
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Pejman
authors.initials: P
authors.lastname: Ghanouni
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Kim Butts
authors.initials: KB
authors.lastname: Pauly
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Pauly
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging; D000071538:Cortical Bone / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D064847:Multimodal Imaging / Q000379:methods; D019047:Phantoms, Imaging; D012815:Signal Processing, Computer-Assisted; D012886:Skull / Q000000981:diagnostic imaging
keywords: MR image-guided radiation therapy; MR-guided focused ultrasound planning; MR/PET attenuation correction; bone MRI; ultrashort echo time; zero echo time