UCSF

Introduction

Trabecular bone score (TBS) was proposed as a method to indirectly assess the vertebral microarchitecture from Dual X-ray Absorptiometry (DXA) images, which are have a projectional geometry that does not reflect 3D structure. In this study, we evaluated the extent to which TBS is affected by the variable angulation of the vertebra in the body and the presence of aortic calcifications that overly the vertebra.

Methods

All programming was done on Matlab. The CT data was provided by Dr Sundeep Khosla’s group at the Mayo Clinic from their study of age-related bone loss and fracture. Partial vertebral masks, calibration data, and coordinate transforms, were provided by Professor Engelke’s group. Calcified aorta was removed from each slice manually. We computed the TBS of a pure trabecular bone region in a standardized (“bone fixed”) vertebral coordinate system as a gold standard. This was compared via linear regression to the TBS of the entire vertebra in the bone fixed coordinate system and then to the entire vertebra in the native scanner coordinate system. Both comparisons were done with and without the aortic calcium removed.

Results

There was a modest but significant correlation observed between the TBS of pure trabecular bone region and the TBS of the image set in bone-fixed coordinate with the calcified aorta removed. The correlation degraded slightly when calcified aorta was added back in, and degraded heavily when the images were rotated back to their original scanner coordinates. There was a correlation observed between rotation angle and the TBSs between the original and rotated image sets.

Conclusion

There was a significant reduction of correlation between TBS of pure trabecular bone region and the TBS calculated from native images in the scanner coordinate system with aortic calcification. As the angle of rotation increased, greater deviation was noticed between the TBS of the original and the rotated image. We conclude that the poor correlation between the pure trabecular bone and the native TBS raises significant questions about the clinical utility of this technique.