Abbreviated quantitative UTE imaging in anterior cruciate ligament reconstruction

Abstract

Background: Existing ultrashort echo time magnetic resonance imaging (UTE MRI) methods require prohibitively long acquisition times (~ 20-40 min) to quantitatively assess the clinically relevant fast decay T2 component in ligaments and tendons. The purpose of this study was to evaluate the feasibility and clinical translatability of a novel abbreviated quantitative UTE MRI paradigm for monitoring graft remodeling after anterior cruciate ligament (ACL) reconstruction. Methods: Eight patients who had Graftlink™ hamstring autograft reconstruction were recruited for this prospective study. A 3D double-echo UTE sequence at 3.0 Tesla was performed at 3- and 6-months post-surgery. An abbreviated UTE MRI paradigm was established based on numerical simulations and in vivo validation from healthy knees. This proposed approach was used to assess the T2 for fast decay component (T 2 s {T}-{2s}^{\ast } and bound water signal fraction (f bw ) of ACL graft in regions of interest drawn by a radiologist. Results: Compared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for T 2 s {T}-{2s}^{\ast } and f bw over a range of clinically relevant values for ACL grafts. A decrease in T 2 s {T}-{2s}^{\ast } of the intra-articular graft was observed in 7 of the 8 ACL reconstruction patients from 3- to 6-months (- 0.11 ± 0.16 ms, P = 0.10). Increases in T 2 s {T}-{2s} and f bw from 3- to 6-months were observed in the tibial intra-bone graft (ΔT 2 s {\varDelta T}-{2s}^{\ast } : 0.19 ± 0.18 ms, P < 0.05; Δf bw : 4% ± 4%, P < 0.05). Lower T 2 s {T}-{2s}^{\ast } (- 0.09 ± 0.11 ms, P < 0.05) was observed at 3-months when comparing the intra-bone graft to the graft/bone interface in the femoral tunnel. The same comparisons at the 6-months also yielded relatively lower T 2 s {T}-{2s} 0.09 ± 0.12 ms, P < 0.05). Conclusion: The proposed abbreviated 3D UTE MRI paradigm is capable of assessing the ACL graft remodeling process in a clinically translatable acquisition time. Longitudinal changes in T 2 s {T}-{2s}^{\ast } and f bw of the ACL graft were observed.