title: Generation of 3D shape, density, cortical thickness and finite element mesh of proximal femur from a DXA image.
abstract: Areal bone mineral density (aBMD), as measured by dual-energy X-ray absorptiometry (DXA), predicts hip fracture risk only moderately. Simulation of bone mechanics based on DXA imaging of the proximal femur, may help to improve the prediction accuracy. Therefore, we collected three (1-3) image sets, including CT images and DXA images of 34 proximal cadaver femurs (set 1, including 30 males, 4 females), 35 clinical patient CT images of the hip (set 2, including 27 males, 8 females) and both CT and DXA images of clinical patients (set 3, including 12 female patients). All CT images were segmented manually and landmarks were placed on both femurs and pelvises. Two separate statistical appearance models (SAMs) were built using the CT images of the femurs and pelvises in sets 1 and 2, respectively. The 3D shape of the femur was reconstructed from the DXA image by matching the SAMs with the DXA images. The orientation and modes of variation of the SAMs were adjusted to minimize the sum of the absolute differences between the projection of the SAMs and a DXA image. The mesh quality and the location of the SAMs with respect to the manually placed control points on the DXA image were used as additional constraints. Then, finite element (FE) models were built from the reconstructed shapes. Mean point-to-surface distance between the reconstructed shape and CT image was 1.0 mm for cadaver femurs in set 1 (leave-one-out test) and 1.4 mm for clinical subjects in set 3. The reconstructed volumetric BMD showed a mean absolute difference of 140 and 185 mg/cm(3) for set 1 and set 3 respectively. The generation of the SAM and the limitation of using only one 2D image were found to be the most significant sources of errors in the shape reconstruction. The noise in the DXA images had only small effect on the accuracy of the shape reconstruction. DXA-based FE simulation was able to explain 85% of the CT-predicted strength of the femur in stance loading. The present method can be used to accurately reconstruct the 3D shape and internal density of the femur from 2D DXA images. This may help to derive new information from clinical DXA images by producing patient-specific FE models for mechanical simulation of femoral bone mechanics.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland, POB 1627, Kuopio 70211, Finland; Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, Kuopio, Finland, POB 1777, Kuopio 70211, Finland; Diagnostic Imaging Centre, Kuopio University Hospital, Kuopio, Finland, POB 100, Kuopio 70029, Finland; Department of Biomedical Engineering, Lund University, Lund, Sweden, Box 118, Lund 221 00, Sweden. Electronic address: sami.vaananen@uef.fi.
authors.forename: Sami P
authors.initials: SP
authors.lastname: Väänänen
authors.affiliation: Department of Biomedical Engineering, Lund University, Lund, Sweden, Box 118, Lund 221 00, Sweden. Electronic address: lorenzo.grassi@bme.lth.se.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Grassi
authors.affiliation: Department of Orthopaedics, Clinical Sciences, Lund University, Lund, Sweden, Lund 221 85, Sweden. Electronic address: gunnar.flivik@med.lu.se.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Flivik
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland, POB 1627, Kuopio 70211, Finland; Diagnostic Imaging Centre, Kuopio University Hospital, Kuopio, Finland, POB 100, Kuopio 70029, Finland. Electronic address: jukka.jurvelin@uef.fi.
authors.forename: Jukka S
authors.initials: JS
authors.lastname: Jurvelin
authors.affiliation: Department of Biomedical Engineering, Lund University, Lund, Sweden, Box 118, Lund 221 00, Sweden; Department of Orthopaedics, Clinical Sciences, Lund University, Lund, Sweden, Lund 221 85, Sweden. Electronic address: hanna.isaksson@bme.lth.se.
authors.forename: Hanna
authors.initials: H
authors.lastname: Isaksson
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000502:physiology*; D002102:Cadaver; D003198:Computer Simulation; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging* / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D064847:Multimodal Imaging / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: Bone mineral density; DXA; Finite element; Proximal femur; Shape reconstruction; Statistical appearance model