Angle-sensitive MRI for quantitative analysis of fiber-network deformations in compressed cartilage

To demonstrate the feasibility of a novel experimental method to quantitatively analyze fiber-network deformation in compressed cartilage by angle-sensitive magnetic resonance imaging (MRI) of cartilage.

Three knee cartilage samples of an adult sheep were imaged in a high-resolution MRI scanner at 7 T. Main fiber orientation and its "offset" from the direction perpendicular to the bone-cartilage boundary were derived from MR images taken at different orientations with respect to B0. Bending of the collagen fibers was determined from weight-bearing MRI with the load (up to 1.0 MPa) applied over the whole sample surface. A "fascicle" model of the cartilage ultrastructure was assumed to analyze characteristic intensity variations in T2-weighted images under load.

T2-weighted MR images showed a strong variation of the signal intensities with sample orientation. In the T2-weighted weight-bearing series, regions of high signal intensity underwent shifts from the lateral to the central parts in all three cartilage samples. The bending of the collagen fibers was determined to be 27.2°, 35.4°, and 40.0° per MPa, respectively.

Assuming a "fascicle" model, the presented MRI method provides quantitative measures of structural adjustments in compressed cartilage. Our preliminary analysis suggests that cartilage fiber deformation includes both bending and crimping.