title: Volumetric measurements of bone mineral density of the lumbar spine: comparison of three geometrical approximations using dual-energy X-ray absorptiometry (DXA)
abstract: Measurements of bone mineral density using dual-energy X-ray absorptiometry (DXA) gives area values (g cm-2) rather than true volumetric values (g cm-3). To calculate the vertebral volume using planar postero-anterior and lateral DXA values, several different geometrical approximations were used: cubic, cylindrical with a circular cross-section and cylindrical with an elliptical cross-section. The aim of this study was to compare these geometrical approximations with each other and with a reference standard, defined as the volume found on a computed tomographic (CT) scan. L2 and L3 were evaluated in a phantom study. Volume approximations by the cube or cylinder with circular cross-section geometry showed more than a 50% overestimation (range 54-74%). However, the elliptical cylinder approach showed very good agreement: 2.1% and 1.2% for L2 and L3, respectively, when compared to the CT volumes. In addition, we performed four patient studies with both CT and DXA to evaluate the elliptical cylinder estimate in a clinical setting. For L2 and L3, the mean relative difference was less than 2%. We conclude that the elliptical cylinder approach results in the most accurate bone volume estimates in both the phantom and patients.
authors.affiliation: Department of Endocrinology, Free University Hospital, Amsterdam, The Netherlands.
authors.forename: M F
authors.initials: MF
authors.lastname: Schreuder
authors.forename: A P
authors.initials: AP
authors.lastname: van Driel
authors.forename: A
authors.initials: A
authors.lastname: van Lingen
authors.forename: J C
authors.initials: JC
authors.lastname: Roos
authors.forename: C M
authors.initials: CM
authors.lastname: de Ridder
authors.forename: R A
authors.initials: RA
authors.lastname: Manoliu
authors.forename: E F
authors.initials: EF
authors.lastname: David
authors.forename: J C
authors.initials: JC
authors.lastname: Netelenbos
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods* / Q000706:statistics & numerical data; D000328:Adult; D015519:Bone Density; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D014057:Tomography, X-Ray Computed