Abstract
BackgroundExisting 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.MethodsEight 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 } ) and bound water signal fraction (fbw) of ACL graft in regions of interest drawn by a radiologist.ResultsCompared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for {T}_{2s}^{ast } and fbw over a range of clinically relevant values for ACL grafts. A decrease in {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}_{2s}^{ast } and fbw from 3- to 6-months were observed in the tibial intra-bone graft ( {varDelta T}_{2s}^{ast } : 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower {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}_{2s}^{ast } (− 0.09 ± 0.12 ms, P < 0.05).ConclusionThe 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 } and fbw of the ACL graft were observed.
Highlights
Existing ultrashort echo time magnetic resonance imaging (UTE Magnetic resonance imaging (MRI)) methods require prohibitively long acquisition times (~ 20–40 min) to quantitatively assess the clinically relevant fast decay T2* component in ligaments and tendons
Magnetic resonance imaging (MRI) enables non-invasive evaluation of anterior cruciate ligament (ACL) grafts with high tissue contrast, and has been widely used for detecting impingement and graft tears after ACL reconstruction
We proposed and evaluated a novel abbreviated quantitative ultrashort echo time magnetic resonance imaging (UTE MRI) paradigm to characterize the fast decay short graft remodeling
Summary
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 development and validation of robust and objective biomarkers to evaluate the individual graft healing status is critical These biomarkers may aid in implementing optimal rehabilitation protocols to reduce the risk of graft re-rupture and to allow for quick return-to-play. Contrast enhanced and diffusion tensor imaging (DTI) MRI have been utilized to evaluate the revascularization and collagen remodeling of implanted grafts, respectively [13,14,15]. Most of these studies were only conducted at a single time point without longitudinal assessment. In connective tissues including tendons and ligaments, ultrashort echo time (UTE), variable
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