Abbreviated quantitative UTE imaging in anterior cruciate ligament reconstruction

Abstract

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 ($$ {T}_{2s}^{\ast } $$ T 2 s ∗ ) and bound water signal fraction (fbw) 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 $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw over a range of clinically relevant values for ACL grafts. A decrease in $$ {T}_{2s}^{\ast } $$ T 2 s ∗ 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 $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw from 3- to 6-months were observed in the tibial intra-bone graft ($$ {\varDelta T}_{2s}^{\ast } $$ ΔT 2 s ∗ : 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower $$ {T}_{2s}^{\ast } $$ T 2 s ∗ (− 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 $$ {T}_{2s}^{\ast } $$ T 2 s ∗ (− 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 $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw of the ACL graft were observed.