Diffusion tensor imaging of the anterior cruciate ligament graft

Purpose: A great need exists for objective biomarkers to assess graft healing following ACL reconstruction to guide the time of return to sports. The purpose of this study was to evaluate the feasibility and reliability of diffusion tensor imaging (DTI) to delineate the anterior cruciate ligament (ACL) graft and to investigate its diffusion properties using a clinical 3T scanner. Materials and Methods: DTI of the knee (b = 0, 400, and 800 s/mm ², 10 diffusion directions, repeated 16 times for a total of 336 diffusion-weighted volumes) was performed at 3T in 17 patients between 3 and 7 months (mean, 4 months) following ACL reconstruction. Tractography was performed by two independent observers to delineate the ACL graft. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated within the graft. Interrater reliability was assessed using the intraclass correlation coefficient (ICC) and the scan–rescan reproducibility was evaluated based on the percentage coefficient of variance (%CV) across 20 repetition bootknife samples. Results: In all subjects, tractography of the ACL graft was feasible. Quantitative evaluation of the diffusion properties of the ACL graft yielded the following mean ± SD values: FA = 0.23 ± 0.04; MD = 1.30 ± 0.11 × 10 ⁻³ mm ²/s; AD = 1.61 ± 0.12 × 10 ⁻³ mm ²/s, and RD = 1.15 ± 0.11 × 10 ⁻³ mm ²/s. Interrater reliability for the DTI parameters was excellent (ICC = 0.91–0.98). Mean %CVs for FA, MD, AD, and RD were 4.6%, 3.5%, 3.7%, and 4.4%, respectively. Conclusion: We demonstrated the feasibility and reliability of DTI for the visualization and quantitative evaluation of the ACL graft at 3T. Level of Evidence: 3. Technical Efficacy: Stage 1. J. Magn. Reson. Imaging 2017;46:1423–1432.