title: Inverse Correlation at the Hip Between Areal Bone Mineral Density Measured by Dual-Energy X-ray Absorptiometry and Cortical Volumetric Bone Mineral Density Measured by Quantitative Computed Tomography.
abstract: Quantitative computed tomography (QCT) is considered to measure true volumetric bone mineral density (vBMD; mg/cm3) and enables differentiation between cortical and trabecular bone. We aimed to determine the value of QCT by correlating areal BMD (aBMD) by dual-energy X-ray absorptiometry (DXA) with vBMD when using a fixed threshold to delineate cortical from trabecular bone. In a cross-sectional study, 98 postmenopausal women had their hip scanned by DXA and by QCT. At the total hip and the trabecular bone compartment, aBMD correlated significantly with vBMD (r=0.74 and r=0.63; p<0.01, respectively). A significant inverse correlation was found between aBMD and cortical vBMD (r=-0.57; p<0.01). Total hip volume by QCT did not change with aBMD. However, increased aBMD was associated with a decreased trabecular bone volume (r=-0.36; p<0.01) and an increased cortical volume (r=0.69; p<0.01). Changing the threshold used to delineate cortical from trabecular bone from default 350 mg/cm3 to either 300 or 400 mg/cm3 did not affect integral vBMD (p=89) but had marked effects on estimated vBMD at the cortical (p<0.001) and trabecular compartments (p<0.001). Furthermore, increasing the threshold decreased cortical thickness (p<0.001), whereas the strength parameter in terms of buckling ratio increased (p<0.001). Our results show good agreement between aBMD and integral vBMD. However, using a fixed threshold to differentiate cortical from trabecular bone causes an apparent increase in cortical volume with a decrease in cortical density as aBMD increases. This may be caused by the classification of a larger part of the transition zone as cortical bone with increased aBMD.
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark. Electronic address: anne_kristine_am@hotmail.com.
authors.forename: Anne Kristine
authors.initials: AK
authors.lastname: Amstrup
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Niels Frederik Breum
authors.initials: NF
authors.lastname: Jakobsen
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Lomholt
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Tanja
authors.initials: T
authors.lastname: Sikjaer
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Leif
authors.initials: L
authors.lastname: Mosekilde
authors.affiliation: Osteoporosis Clinic, Department of Endocrinology and Internal Medicine (MEA), THG Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Rejnmark
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000368:Aged; D015519:Bone Density; D001851:Bone Diseases, Metabolic / Q000175:diagnosis*; D057186:Comparative Effectiveness Research; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008875:Middle Aged; D009929:Organ Size; D015203:Reproducibility of Results; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: DXA; QCT; aBMD; vBMD