title: Performance Evaluation of Material Decomposition With Rapid-Kilovoltage-Switching Dual-Energy CT and Implications for Assessing Bone Mineral Density.
abstract: OBJECTIVE
  The purpose of this article is to quantitatively investigate the accuracy and performance of dual-energy CT (DECT) material density images and to calculate the areal bone mineral density (aBMD) for comparison with dual-energy x-ray absorptiometry (DEXA).
  
  
  METHODS
  A rapid-kilovoltage-switching DECT scanner was used to create material density images of various two-material phantoms of known concentrations under different experimental conditions. They were subsequently also scanned by single-energy CT and DEXA. The total uncertainty and accuracy of the DECT concentration measurements was quantified by the root-mean-square (RMS) error, and linear regression was performed to evaluate measurement changes under varying scanning conditions. Alterations to accuracy with concentric (anthropomorphic) phantom geometry were explored. The sensitivity of DECT and DEXA to changes in material density was evaluated. Correlations between DEXA and DECT-derived aBMD values were assessed.
  
  
  RESULTS
  The RMS error of DECT concentration measurements in air ranged from 9% to 244% depending on the materials. Concentration measurements made off-isocenter or with a different DECT protocol were slightly lower (≈ 5%), whereas measurement in scattering conditions resulted in a reduction of 8-27%. In concentric phantoms, higher-attenuating material in the outer chamber increased measured values of the inner material for all methods. DECT was more sensitive than DEXA to changes in BMD at 2 mg/mL K2HPO4. Measurements of aBMD using DECT and DEXA were highly correlated (R(2) = 0.98).
  
  
  CONCLUSIONS
  DECT material density images were linear in response but prone to poor accuracy and biases. DECT-based aBMD could be used to monitor relative change in bone density.
authors.affiliation: 1 Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, 1155 Pressler, Unit 1352, Houston, TX 77030.
authors.forename: John M S
authors.initials: JM
authors.lastname: Wait
authors.forename: Dianna
authors.initials: D
authors.lastname: Cody
authors.forename: Aaron K
authors.initials: AK
authors.lastname: Jones
authors.forename: John
authors.initials: J
authors.lastname: Rong
authors.forename: Veerabhadran
authors.initials: V
authors.lastname: Baladandayuthapani
authors.forename: S Cheenu
authors.initials: SC
authors.lastname: Kappadath
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation / Q000379:methods*; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000000981:diagnostic imaging* / Q000502:physiology*; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
keywords: bone mineral density; dual-energy CT; dual-energy x-ray absorptiometry; osteoporosis