Cortical bone vessel identification and quantification on contrast-enhanced MR images

Area of Science:

• Biomedical Engineering
• Bone Biology
• Medical Imaging

Background:

• Cortical bone porosity significantly impacts bone strength, but its biological drivers remain unclear.
• Vessels and adipocytes within cortical pores are implicated in pore expansion mechanisms.
• Existing imaging techniques like Dynamic Contrast-Enhanced MRI (DCE-MRI) have not been applied to visualize vessels within cortical bone.

Purpose of the Study:

• To develop and validate a multimodal imaging pipeline combining DCE-MRI and high-resolution peripheral quantitative computed tomography (HR-pQCT) for detecting vessel-filled cortical bone pores.
• To quantify vessel characteristics within cortical bone, such as vessel volume fraction, density, and average volume.
• To investigate the biological drivers of cortical porosity and pore expansion.

Main Methods:

• A cohort of 19 healthy volunteers (mean age 63) underwent simultaneous HR-pQCT and 3T DCE-MRI of the tibia.
• A novel image processing pipeline was developed to register DCE-MRI data to HR-pQCT bone structure and identify vessel-filled voxels using a hierarchical k-means clustering algorithm.
• A validation phantom with known channel sizes was used to assess the pipeline's spatial resolution and accuracy.

Main Results:

• The developed pipeline successfully detected vessels within cortical bone pores in human subjects, with a mean vessel volume fraction of 2.2%.
• Quantified metrics included mean vessel density (0.68 vessel/mm³) and average vessel volume (0.032 mm³/vessel).
• The imaging technique demonstrated high accuracy for detecting channels ≥250 µm in diameter, with performance degradation for smaller vessels.

Conclusions:

• A multimodal imaging and processing pipeline was successfully established for detecting vessels in cortical bone.
• The technique's effectiveness is limited by the in-plane spatial resolution of DCE-MRI for detecting very small vessels (<250 µm).
• This approach offers a novel tool for investigating the biological systems contributing to cortical bone porosity and expansion.