title: Calibration of cone beam CT using relative attenuation ratio for quantitative assessment of bone density: a small animal study.
abstract: OBJECTIVE
  Cone beam computed tomography (CBCT) has the disadvantage of providing non-quantitative results for bone density determination. The aim of this study is to calibrate CBCT results by using an internal reference (such as muscle) for quantitatively assessing bone density.
  
  
  METHODS
  We developed a new method using the relative attenuation ratio between two nearby materials (such as bone and muscle) for systemic error correction in CBCT that depends on the relative object position in the image volume. Phantom calibration was performed to calculate the acquired attenuation ratio in Hounsfield units (HU), comparable to the results from clinical multislice spiral computed tomography (MSCT). In addition, a small animal study with an osteoporotic rat model was evaluated to show the feasibility of this presented method to quantitatively assess bone density using a CBCT system.
  
  
  RESULTS
  The phantom study results showed that the calibration process successfully corrected the systemic inaccuracy from CBCT, and the calibrated HU values agreed with the values measured from MSCT. In the small animal study, the quantitative bone densities assessed from the calibrated CBCT results were consistent with the results from MSCT data.
  
  
  CONCLUSIONS
  A practical method to quantitatively estimate attenuation (HU) values for bone tissues from CBCT scans that are comparable to MSCT scans is proposed. The method may improve the quantification ability of CBCT scanning without any additional hardware requirements.
authors.affiliation: Department of Medical Physics in Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, 69120 , Heidelberg, Germany.
authors.forename: Yifei
authors.initials: Y
authors.lastname: Liu
authors.forename: Tobias
authors.initials: T
authors.lastname: Bäuerle
authors.forename: Leyun
authors.initials: L
authors.lastname: Pan
authors.forename: Antonia
authors.initials: A
authors.lastname: Dimitrakopoulou-Strauss
authors.forename: Ludwig G
authors.initials: LG
authors.lastname: Strauss
authors.forename: Christian
authors.initials: C
authors.lastname: Heiss
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schnettler
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Semmler
authors.forename: Liji
authors.initials: L
authors.lastname: Cao
mesh_terms: D000818:Animals; D015519:Bone Density; D002138:Calibration; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D004195:Disease Models, Animal; D008962:Models, Theoretical; D010024:Osteoporosis / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D051381:Rats; D015203:Reproducibility of Results; D012447:Sacrum / Q000000981:diagnostic imaging*