In this study we introduce two non-linear structural measures based on the Standard Hough-Transform (SHT) that are applied to high resolution MR-images of human trabecular bone specimens in order to predict biomechanical properties. The results are compared to bone mineral density (BMD) and linear morphometric parameters.
Axial MR-images (voxel-size: 117x156x300 mm3) of 33 human femoral and 10 spinal specimens are obtained using a 3D-gradient-echo-sequence. After measurement of BMD by quantitative computed tomography (QCT) all specimens are tested destructively for maximum compressive strength (MCS). The SHT is applied to the binarized and Sobel-filtered images and the peak-value (maxH) and its corresponding bin (posH) of the normalized Hough-spectrum are determined as well as linear measures (apparent bone fraction (app.BV/TV), apparent trabecular separation (app.Tb.Sp), apparent trabecular perimeter per unit area (app.Tb.Perim)).
For the spinal [femoral] specimens, R2 for MCS vs. maxH is 0.72 (p=0.004) [0.49 (p<0.001)], R2 for MCS vs. posH is 0.56 (p=0.013) [0.55 (p<0.001)], and R2 for MCS vs. BMD is 0.43 (p=0.041) [0.72 (p<0.001)].
Correlations of the conventional, linear morphometric parameters and MCS are lower than those for the SHT-based measures or BMD, ranging from 0.20 (p=0.003) for app.BV/TV to 0.46 (p<0.001) for app.Tb.Sp.
Prediction of MCS by maxH, posH, or BMD alone is improved by combination with the linear morphometric parameters in a linear regressional model (R2 =0.79).
In conclusion, the biomechanical strength of human trabecular bone in vitro can effectively be predicted from High-Resolution MR-images by structural measures based on SHT. In the vertebral specimens these are superior to BMD or conventional structural measures in predicting bone strength.