E-Poster Presentation 30th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2020

Automated regional segmentation of the murine bone cortex exposes microstructural diversity in porosity

Jacob Trend, Alisha Sharma, Katrin Deinhardt, Philipp Schneider and Claire Clarkin

Objective: Cortical bone is densely vascularised and exceptional to study as it provides physical compartmentalisation of mineral and vascular compartments allowing 3D reconstruction of vessel spatial heterogeneity. Previously, we provided the first evidence that age-related effects on murine bone porosity depend on the locality of the intracortical vasculature^(1). Herein, our aim was to develop an automated means to segment cortical bone for regional assessment of microstructural heterogeneity.

Method: Synchrotron X-Ray computed tomography scans were undertaken at the tibiofibular junction of 13-month c57BL6 mice and reconstructed to form 8-bit greyscale image stacks. To standardise region separation across bone samples into anterior posterior, lateral, and medial regions, the Bone J moment of interia function⁽²⁾ was used to align each bone to its principle axis (Fig.1). Porosity was extracted as described⁽¹⁾ and sorted into osteocyte lacunae (La.) and vascular canals (Ca.).

Results: Cortical porosity was identified as highest within the posterior (2.04%±0.008) and medial regions (1.65%±0.339) and lowest in the lateral (1.19%±0.192) and anterior (1.09%±0.1198) compartments. Intra-region variability was further exposed in Ca. circumference, with posterior Ca. larger than medial (65.39µm±3.03 vs 36.37µm± 6.22; p<0.01). Ca. circularity was less in the anterior versus all other regions, while Ca. volume density was greater in the posterior than the medial (0.51% ±0.099 vs 0.29%±0.056, p<0.05). La. circumference was greatest in the medial and lowest in the anterior region (23.27µm ±1.43 vs 18.3µm ± 1.17, p<0.05). La. volume density and La. number density were also highest in the medial and lowest in the anterior region (1.64±0.34 vs 2.47±0.11, p=0.019, and 0.66±0.13, 1.81±0.028, p=0.001, respectively).

Conclusion: Our study highlights an importance for regional assessment of cortical heterogeneity in the study of bone phenotypes, which could improve understanding into alterations in structure-function characteristics of cortical porosity during disease progression.

References

(1) Núñez, J., Goring, A., Javaheri, B., Razi, H., Gomez-Nicola, D., Hesse, E., Pitsillides, A., Thurner, P., Schneider, P. and Clarkin, C., 2018. Regional diversity in the murine cortical vascular network is revealed by synchrotron X-ray tomography and is amplified with age. European Cells and Materials, 35, pp.281-299.

(2) Doube, M., Kłosowski, M., Arganda-Carreras, I., Cordelières, F., Dougherty, R., Jackson, J., Schmid, B., Hutchinson, J. and Shefelbine, S., 2010. BoneJ: Free and extensible bone image analysis in ImageJ. Bone, 47(6), pp.1076-1079.