title: Assessing bone status beyond BMD: evaluation of bone geometry and porosity by quantitative ultrasound of human finger phalanges.
abstract: In an in vitro study, we found significant associations between QUS variables and properties and geometrical parameters of the compact bone of human finger phalanges. QUS variables were not only related to BMD but also to other skeletal properties, which explained 70% of the variability of speed of sound.
  
  
  BACKGROUND
  Transverse transmission quantitative ultrasound (QUS) measurements at the finger phalanges are known to be correlated with BMD and to predict osteoporotic fractures. To determine which other skeletal properties are affected by ultrasound, we investigated the impact of density, geometry, and porosity on QUS variables in vitro.
  
  
  METHODS
  Ultrasound variables were correlated with density, porosity, and geometrical characteristics of cortical bone. Additionally, we tested which combinations of geometry and bone properties best predicted the ultrasound results observed. Forty-four proximal phalanges from the middle finger were investigated at their distal metaphysis, similar to the typical clinical measurement procedure. Donor age ranged from 52 to 98 years (15 males and 29 females; mean age, 80.9 +/- 9.4 years). QUS variables were measured on the metaphysis of the phalanges using the DBMSonic 1200. Quantitative CT was used for the measurement of BMD, and high-resolution MRI was used for the measurement of porosity and geometrical variables.
  
  
  RESULTS
  Speed of sound (SOS) and the clinically used variable AD-SOS correlated significantly with area, relative area, density, and porosity of the compact bone (R2 = 0.28-0.58, p < 0.0001). Signal amplitude correlated significantly only with relative area of the compact bone and area of the medullary canal (R2 = 0.18-0.20, p < 0.01). The combination of cortical area, density, and porosity improved the determination of SOS to R2 = 0.70, with a residual unexplained variability of 54 m/s (3.2%).
  
  
  CONCLUSIONS
  These results clarify the impact of skeletal properties on QUS variables. SOS is affected by cortical area, cortical bone density, and cortical porosity, whereas attenuation only depends on geometry of the medulla. AD-SOS, the variable routinely measured in clinical practice, is primarily affected by cortical area. QUS of the finger phalanges is not only related to BMD but also to other skeletal properties.
authors.affiliation: Medizinische Physik, Klinik für Diagnostische Radiologie, Universitätsklinikum Schleswig-Holstein, Kiel, Germany.
authors.forename: Satoru
authors.initials: S
authors.lastname: Sakata
authors.forename: Reinhard
authors.initials: R
authors.lastname: Barkmann
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Lochmüller
authors.forename: Martin
authors.initials: M
authors.lastname: Heller
authors.forename: Claus-Christian
authors.initials: CC
authors.lastname: Glüer
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D005385:Fingers / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D008875:Middle Aged; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography