The pattern of trabecular bone microarchitecture in the distal femur of typically developing children and its effect on processing of magnetic resonance images

Abstract

Introduction: 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.

Materials and 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.

Keywords: Bone microarchitecture; Children; Magnetic resonance imaging; Pediatrics.

Conflict of interest statement

Conflicts of interest: The authors declare that they have no conflicts of interest.

Copyright © 2013 Elsevier Inc. All rights reserved.

Figures

Figure 1

A visual depiction of the procedure used to assess trabecular bone microarchitecture in the distal femur. Coronal (A) and sagittal (B) scout images show the region of interest in the distal femur where 26 magnetic resonance images were collected immediately above the growth plate. The 20 most central raw images (C) were filtered using low-pass filter-based correction algorithm and then reversed in gray scale to optimize visualization (D). The lateral aspect of the trabecular bone in the distal femur was masked by identifying the trochlear groove (large arrow), extending perpendicular to the posterior portion of the bone (medium arrow) and then following the boundary between the trabecular bone from the cortical shell (small arrows). In each image, eight samples were taken from the cortical shell (E) and the three samples with the highest signal intensity were used to separate the region of interest into bone and marrow phases (binarized; F). As described by Majumdar et al. [5], measures of trabecular bone microarchitecture were calculated for each of the twenty binarized images and the averages are reported.

Figure 2

Scatter plots show the relationships between proximal distance from the growth plate in the distal femur and A) apparent trabecular bone volume to total bone volume, B) apparent trabecular number, C) apparent trabecular thickness and D) apparent trabecular separation in typically developing children.

Figure 3

Scatter plots show the relationships between estimates of apparent trabecular bone volume to total bone volume (appBV/TV) from a total image set in the distal femur (i.e., 20 images, 20IM) and estimates from A) 10 images (10IM), B) 5 images (5IM), C) 3 images (3IM), and 1 image (1IM).

Figure 4

Scatter plots show the relationships between estimates of apparent trabecular bone number (appTb.N) from a total image set in the distal femur (i.e., 20 images, 20IM) and estimates from A) 10 images (10IM), B) 5 images (5IM), C) 3 images (3IM), and 1 image (1IM).

Figure 5

Scatter plots show the relationships between estimates of apparent trabecular bone thickness (appTb.Th) from a total image set in the distal femur (i.e., 20 images, 20IM) and estimates from A) 10 images (10IM), B) 5 images (5IM), C) 3 images (3IM), and 1 image (1IM).

Figure 6

Scatter plots show the relationships between estimates of apparent trabecular bone separation (appTb.Sp) from a total image set in the distal femur (i.e., 20 images, 20IM) and estimates from A) 10 images (10IM), B) 5 images (5IM), C) 3 images (3IM), and 1 image (1IM).