title: Time dependency of bone density estimation from computed tomography with intravenous contrast agent administration.
abstract: Our study has demonstrated that in contrast-enhanced multi-detector computed tomography (MDCT)-based bone density measurements, the scan delay time after contrast agent administration is a statistically significant variable for the derivation of quantitative computed tomography (QCT)-equivalent bone mineral density (BMD) values.
  
  
  BACKGROUND
  Earlier investigators have proposed to derive QCT-equivalent BMD values from contrast-enhanced MDCT scans by using a merely density-based conversion equation. The purpose of this study was to investigate whether the scan delay after intravenous (IV) contrast agent administration might affect BMD values derived in this way.
  
  
  METHODS
  A retrospective data analysis was performed on 198 subjects who underwent standardized biphasic MDCT. Average densities values (in Hounsfield units) of lumbar vertebral bodies 1 to 3 (L1-L3) were compared between phases I and II of the biphasic MDCT scan. Furthermore, QCT-equivalent BMD (BMDQCT) values were calculated using a previously published conversion equation.
  
  
  RESULTS
  Paired t-test analysis revealed that IV contrast agent administration leads to a statistically significant increase (8.6 %; p < 0.0001) in overall density of L1-L3 from phases I to II. Moreover, comparison of BMDQCT values between phases I and II reveals a change from osteoporotic to osteopenic in 4.5 % of the study population and from osteopenic to normal for 11.1 % of the subjects. Furthermore, it was revealed that the density increase from phases I to II shows a weak, yet statistically significant (p < 0.001) age dependency.
  
  
  CONCLUSIONS
  Our study demonstrates that the use of a mere density-based conversion equation for deriving BMDQCT from MDCT scans ignores time dependency as an important variable. Furthermore, our results indicate that the actual age-dependent BMD itself might be another relevant variable that needs to be included in a MDCT-to-QCT conversion equation.
authors.affiliation: Department of Radiology, Charite Campus Mitte, Universitaetsmedizin Berlin, Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Acu
authors.forename: M
authors.initials: M
authors.lastname: Scheel
authors.forename: A S
authors.initials: AS
authors.lastname: Issever
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015519:Bone Density / Q000502:physiology; D003287:Contrast Media / Q000008:administration & dosage; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D015663:Osteoporosis, Postmenopausal / Q000000981:diagnostic imaging / Q000503:physiopathology; D012189:Retrospective Studies; D012737:Sex Factors; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003287:Contrast Media