title: Deriving Hounsfield units using grey levels in cone beam computed tomography.
abstract: OBJECTIVE
  an in vitro study was performed to investigate the relationship between grey levels in dental cone beam CT (CBCT) and Hounsfield units (HU) in CBCT scanners.
  
  
  METHODS
  a phantom containing 8 different materials of known composition and density was imaged with 11 different dental CBCT scanners and 2 medical CT scanners. The phantom was scanned under three conditions: phantom alone and phantom in a small and large water container. The reconstructed data were exported as Digital Imaging and Communications in Medicine (DICOM) and analysed with On Demand 3D(R) by Cybermed, Seoul, Korea. The relationship between grey levels and linear attenuation coefficients was investigated.
  
  
  RESULTS
  it was demonstrated that a linear relationship between the grey levels and the attenuation coefficients of each of the materials exists at some "effective" energy. From the linear regression equation of the reference materials, attenuation coefficients were obtained for each of the materials and CT numbers in HU were derived using the standard equation.
  
  
  CONCLUSIONS
  HU can be derived from the grey levels in dental CBCT scanners using linear attenuation coefficients as an intermediate step.
authors: University of Texas Health Science Center at San Antonio (UTHSCSA), Dental Diagnostic Science, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. mah@uthscsa.edu
authors: P
authors: P
authors: Mah
authors: T E
authors: TE
authors: Reeves
authors: W D
authors: WD
authors: McDavid
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D003765:Models, Dental; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement; D019252:Radiography, Dental, Digital / Q000295:instrumentation* / Q000379:methods; D011873:Radiology Information Systems; D012016:Reference Values