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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 T<inf>2</inf> 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 T<inf>2</inf> for fast decay component (T 2 s {T}-{2s}^{\ast } and bound water signal fraction (f <inf>bw</inf> ) 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 <inf>bw</inf> 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 <inf>bw</inf> 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 <inf>bw</inf> : 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 <inf>bw</inf> of the ACL graft were observed.