Micro-computed tomography (microCT) offers a three-dimensional (3D), high-resolution technique for the visualisation and analysis of bone microstructure. With carefully designed longitudinal studies, it can be expanded to capture time-lapse changes in microstructure (4D) and using contrast-enhanced microCT also capture cartilage morphometry and whole joint measures - known together as quantitative morphometric analysis (QMA). However, one of the main challenges in quantitative analysis of joint images is sensitivity to joint pose and alignment, which may influence measures related to both joint space and joint biomechanics. This challenge requires reproducible protocols in both the data acquisition and image processing stages of the study workflow.
In this presentation, I present a comprehensive microCT imaging protocol for reproducible and efficient QMA of in situ mouse tibio-femoral joint. This work consists of a diffusion kinetics study for a known cationic iodinated contrast agent (CA4+) for QMA of the cartilage, and a joint positioning and image processing workflow for whole joint QMA. Secondly, I demonstrate a novel automatic, efficient, and model-invariant image preprocessing pipeline that allows for highly reproducible 3D QMA of the joint.
The joint positioning and image processing workflow was established by developing a novel positioning device to control joint pose during scanning, and a spherical harmonics-based image processing workflow to ensure consistent alignment during image processing. The pipeline addresses the joint pose problem by deploying two modules: an alignment module and a subdivision module. Alignment is achieved by representing the tibia in its basic form using lower degree spherical harmonic basis functions and aligning using principal component analysis. The second module subdivides the joint into lateral and medial VOIs via a watershedding approach based on persistence homology. Joint QMA evaluation of the workflow showed excellent reproducibility; intraclass correlation coefficients ranged from 0.794 to 0.930, confirming that the imaging protocol enables reproducible and efficient QMA of joint structures in preclinical models, and that contrast agent injection did not cause significant alteration to the measured parameters. Furthermore, processing time and technical requirements were reduced compared to manual processing in previous studies.