Depth-dependent changes in cartilage T2 under compressive strain: a 7T MRI study on human knee cartilage

Area of Science:

• Biomedical Engineering
• Orthopedics
• Medical Imaging

Background:

• Articular cartilage is a load-bearing tissue susceptible to damage from mechanical strain.
• Accurate assessment of cartilage strain is crucial for understanding joint health and disease.
• Magnetic Resonance Imaging (MRI) offers non-invasive methods for tissue characterization.

Purpose of the Study:

• To evaluate the potential of T2 relaxation time changes (ΔT2) as an indirect measure of in situ cartilage strain.
• To investigate the relationship between local compressive strain and ΔT2 across the full depth of human tibial and femoral articular cartilage.

Main Methods:

• Human osteochondral samples were subjected to controlled compressive strains in a 7T MRI scanner.
• T2 values were calculated from 3D double echo steady state (DESS) images at various strain levels.
• Depth-dependent strains were estimated, and ΔT2 was determined by subtracting unloaded from strained images.
• Linear modeling was used to correlate local strain with ΔT2.

Main Results:

• Bulk average T2 values showed minimal changes under strain, masking local variations.
• Local ΔT2 varied significantly with depth within the cartilage.
• Significant correlations were found between in situ strain and ΔT2 in both tibial and femoral cartilage.
• Higher correlation coefficients were observed for tibial cartilage compared to femoral cartilage.

Conclusions:

• Bulk average T2 changes are inadequate for quantifying cartilage strain due to the loss of local information.
• High-resolution, local ΔT2 measurements show promise as a surrogate for cartilage strain.
• Further research is needed to understand confounding factors like age, joint surface, and degeneration on the strain-ΔT2 relationship.