T2* MR Relaxometry and Ligament Volume Are Associated with the Structural Properties of the Healing ACL

Our objective was to develop a non-invasive magnetic resonance (MR) method to predict the structural properties of a healing anterior cruciate ligament (ACL) using volume and T-2* relaxation time. We also compared our T-2*-based structural property prediction model to a previous model utilizing signal intensity, an acquisition-dependent variable. Surgical ACL transection followed by no treatment (i.e., natural healing) or bio-enhanced ACL repair was performed in a porcine model. After 52 weeks of healing, high-resolution MR images of the ACL tissue were collected. From these images, ligament volumes and T-2* maps were established. The structural properties of the ligaments were determined via tensile testing. Using the T-2* histogram profile, each ligament voxel was binned based on its T-2* value into four discrete tissue sub-volumes defined by specific T-2* intervals. The linear combination of the ligament sub-volumes binned by T-2* value significantly predicted maximum load, yield load, and linear stiffness (R-2=0.92, 0.82, 0.88; p<0.001) and were similar to the previous signal intensity based method. In conclusion, the T-2* technique offers a highly predictive methodology that is a first step towards the development of a method that can be used to assess ligament healing across scanners, studies, and institutions. (c) 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:492-499, 2014.