T2* mapping in an equine articular groove model: Visualizing changes in collagen orientation

Area of Science:

• Biomedical Imaging
• Orthopedics
• Biomaterials Science

Background:

• Articular cartilage collagen evaluation is crucial for diagnosing joint diseases.
• Post-traumatic arthritis can lead to subtle cartilage damage that is difficult to detect.
• T2* mapping is an emerging magnetic resonance imaging (MRI) technique with potential for non-invasive cartilage assessment.

Purpose of the Study:

• To investigate the utility of T2* mapping in differentiating healthy, subtly damaged, and associated lesion sites in articular cartilage.
• To assess T2* relaxation times in an equine groove model of post-traumatic arthritis.
• To correlate T2* mapping findings with collagen orientation changes observed via polarized light microscopy.

Main Methods:

• Utilized an equine groove model with surgically induced cartilage damage in carpal joints.
• Performed 7.0-T whole-body MRI with gradient echo multi-echo sequences for T2* mapping.
• Analyzed T2* relaxation times in grooved, contralateral control, and "kissing site" cartilage areas.
• Assessed collagen fiber orientation using Picrosirius Red staining and polarized light microscopy (PLM).

Main Results:

• T2* relaxation times were significantly lower in surgically grooved cartilage compared to contralateral healthy sites.
• "Kissing sites" (opposite to grooves) exhibited higher average T2* relaxation times than the grooved areas.
• PLM revealed mild alterations in collagen fiber orientation, particularly around blunt grooves, correlating with T2* changes.

Conclusions:

• T2* mapping effectively distinguishes between healthy and early-stage damaged articular cartilage in the equine groove model.
• The technique can differentiate T2* relaxation times between damaged cartilage and associated "kissing lesions."
• T2* mapping shows promise as a non-invasive tool for evaluating subtle cartilage damage and associated pathologies in joint diseases.