title: Susceptibility mapping of air, bone, and calcium in the head.
abstract: OBJECTIVE
  To demonstrate the mapping of structures with high susceptibility values, such as the sinuses, bones and teeth, using short echo times.
  
  
  METHODS
  Four in vivo datasets were collected with a gradient-echo sequence (TE1 = 2.5 ms, TE2 = 5 ms and TE3 = 7.5 ms). Complex division was performed to remove the phase offset term and generate the phase at TE = 2.5 ms. Susceptibility maps were generated from unwrapped phase images, using a geometry-constrained iterative algorithm, by preserving phase information in the extracerebral tissues. The susceptibility results were improved by updating the missing phase information inside structures with no signal using the predicted phase at each iteration step. Simulated phase images of a three-dimensional brain model and tooth phantom were used to validate the proposed method.
  
  
  RESULTS
  Improved susceptibility maps were obtained once the phase information in the extracerebral tissue region was incorporated, for both the model and in vivo data. For in vivo data, the average susceptibilities of air (sphenoid sinus), bone and calcium (teeth) were found to be (in ppm): Δχ(sinus-tissue)  = +9.2 ± 1.3, Δχ(bone-tissue)  = -2.1 ± 0.6 and Δχ(teeth-tissue)  = -3.3 ± 1.2, respectively.
  
  
  CONCLUSIONS
  High susceptibility structures with little or no signal can be imaged using quantitative susceptibility mapping and can be used to improve background field removal.
authors.affiliation: School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada.
authors.forename: Sagar
authors.initials: S
authors.lastname: Buch
authors.affiliation: School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada.
authors.forename: Saifeng
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Radiology, Wayne State University, Detroit, Michigan, USA.
authors.forename: Yongquan
authors.initials: Y
authors.lastname: Ye
authors.affiliation: Department of Radiology, Wayne State University, Detroit, Michigan, USA.
authors.forename: Yu-Chung Norman
authors.initials: YC
authors.lastname: Cheng
authors.affiliation: Department of Radiology, Wayne State University, Detroit, Michigan, USA.
authors.forename: Jaladhar
authors.initials: J
authors.lastname: Neelavalli
authors.affiliation: School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada.|Department of Radiology, Wayne State University, Detroit, Michigan, USA.|The MRI Institute for Biomedical Research, Detroit, Michigan, USA.
authors.forename: E Mark
authors.initials: EM
authors.lastname: Haacke
mesh_terms: D000388:Air; D000465:Algorithms; D001931:Brain Mapping / Q000379:methods; D002118:Calcium / Q000032:analysis*; D003198:Computer Simulation; D006257:Head / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012886:Skull / Q000033:anatomy & histology
chemical_list: D002118:Calcium
keywords: air-tissue interfaces; imaging bone; imaging sinuses; imaging teeth; phase imaging; quantitative susceptibility mapping