Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments

Tendons and ligaments are dense, fibrous connective tissues that facilitate transmission of loads from muscle to bone (tendon) or from bone to bone (ligament). These tissues are subjected to wear and tear from day-to-day mechanical usage leading to sprains, tendinopathies, or ruptures, each of which is a major source of musculoskeletal disability. Clinically, the diagnosis of tendon and ligament injury is based on a clinical examination as well as magnetic resonance imaging (MRI) of the relevant tissues. MRI is a reliable, non-invasive tool for detecting large and complete tears; however, conventional T1 and T2-weighted grayscale images exhibit poor contrast and a low signal-to-noise ratio which makes identification of low-grade injuries more challenging to delineate. Therefore, there exists a need for reliable, quantitative and more robust imaging approaches to assess tendon and ligament microstructure and integrity. One of these MR approaches is diffusion tensor imaging (DTI), an advanced MRI technique primarily used in neuroimaging applications. DTI assesses tissue microstructural organization by quantifying the 3D diffusion of water molecules within tissues. It relies on the basic diffusion principle that water molecules diffuse more readily along (i.e., parallel to), rather than across physical barriers (e.g., collagen fibers). Diffusion of water molecules can be quantified by the diffusion tensor in each voxel, whereby the magnitude and orientation of water diffusion can be computed throughout the tissue, thus revealing the fiber microstructure. The primary aims of the proposed studies are to demonstrate applicability and reliability of the DTI technique for tendons and ligaments, and determine the sensitivity of b-values to DTI derived parameters of tissue integrity. This is the first study to show feasibility and applicability of DTI on Tendons and Ligaments at ultra-high magnetic fields with high resolutions and measure DTI metrics from both tissue types. High Fractional Anisotropy values of 0.67 for semitendinosus tendons and 0.66 for medial collateral ligaments shows the highly anisotropic nature of these soft connective tissues.Axial diffusivity is about 3 times the radial diffusivity which shows diffusion directional anisotropy indicating diffusion preference along the fibers then across them. The present study showed fiber tractography of these tissues at ultra-high magnetic fields with a histological correlation confirming the highly-organized parallel collagen fiber microstructure. Diffusion tensor imaging is sensitive to the diffusional anisotropy differences and can show microstructural differences between tendons and ligaments through DTI metrics at 11. 7 T field strength. The current work also found the most feasible range of b-values of 300-600 s/mm2 which will be best suited for these tissue types at the given magnetic field strength of 11.7T and get more reliable DTI measurements. DTI metrics can provide insight into 3D tissue integrity and organization. Fiber tractography graphically supplements the quantitative DTI data. The quantitative and graphical capabilities of DTI provide more rigorous information regarding tendon and ligament structural integrity in comparison to conventional MRI.