title: The pattern of trabecular bone microarchitecture in the distal femur of typically developing children and its effect on processing of magnetic resonance images.
abstract: BACKGROUND
  Magnetic resonance imaging (MRI) is used to assess trabecular bone microarchitecture in humans; however, image processing can be labor intensive and time consuming. One aim of this study was to determine the pattern of trabecular bone microarchitecture in the distal femur of typically developing children. A second aim was to determine the proportion and location of magnetic resonance images that need to be processed to yield representative estimates of trabecular bone microarchitecture.
  
  
  METHODS
  Twenty-six high resolution magnetic resonance images were collected immediately above the growth plate in the distal femur of 6-12year-old typically developing children (n=40). Measures of trabecular bone microarchitecture [i.e., apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th) and trabecular separation (appTb.Sp)] in the lateral aspect of the distal femur were determined using the twenty most central images (20IM). The average values for appBV/TV, appTb.N, appTb.Th and appTb.Sp from 20IM were compared to the average values from 10 images (10IM), 5 images (5IM) and 3 images (3IM) equally dispersed throughout the total image set and one image (1IM) from the center of the total image set using linear regression analysis. The resulting mathematical models were cross-validated using the leave-one-out technique.
  
  
  RESULTS
  Distance from the growth plate was strongly and inversely related to appBV/TV (r(2)=0.68, p<0.001) and appTb.N (r(2)=0.92, p<0.001) and was strongly and positively related to appTb.Sp (r(2)=0.86, p<0.001). The relationship between distance from the growth plate and appTb.Th was not linear (r(2)=0.06, p=0.28), but instead it was quadratic and statistically significant (r(2)=0.54, p<0.001). Trabecular bone microarchitecture estimates from 10IM, 5IM, 3IM and 1IM were not different from estimates from 20IM (p>0.05). However, there was a progressive decrease in the strength of the relationships as a smaller proportion of images were used to predict estimates from 20IM (r(2)=0.98 to 0.99 using 10IM, 0.94 to 0.96 using 5IM, 0.87 to 0.90 using 3IM and 0.66 to 0.72 using 1IM; all p<0.001). Using the resulting mathematical models and the leave-one-out cross-validation analysis, measures of trabecular bone microarchitecture estimated from the 10IM and 5IM partial image sets agreed extremely well with estimates from 20IM.
  
  
  CONCLUSIONS
  The findings indicate that partial magnetic resonance image sets can be used to provide reasonable estimates of trabecular bone microarchitecture status in the distal femur of typically developing children. However, because the relative amount of trabecular bone in the distal femur decreases with distance from the growth plate due to a decrease in trabecular number, careful positioning of the region of interest and sampling from throughout the region of interest is necessary.
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. Electronic address: modlesky@udel.edu.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Modlesky
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. Electronic address: dwhitney@udel.edu.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Whitney
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. Electronic address: pcarter@udel.edu.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Carter
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. Electronic address: brianne.mulrooney@gmail.com.
authors.forename: Brianne M
authors.initials: BM
authors.lastname: Allerton
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. Electronic address: jothki@udel.edu.
authors.forename: Joshua T
authors.initials: JT
authors.lastname: Kirby
authors.affiliation: Department of Orthopedics, Nemours AI duPont Hospital for Children, Wilmington, DE, USA. Electronic address: fmiller@nemours.org.
authors.forename: Freeman
authors.initials: F
authors.lastname: Miller
mesh_terms: D002648:Child; D005260:Female; D005269:Femur / Q000033:anatomy & histology*; D006132:Growth Plate / Q000033:anatomy & histology; D048788:Growth and Development; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008954:Models, Biological; D009929:Organ Size
keywords: Bone microarchitecture; Children; Magnetic resonance imaging; Pediatrics