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. 2014 Apr;32(4):492-9.
doi: 10.1002/jor.22563. Epub 2013 Dec 16.

T2 * MR relaxometry and ligament volume are associated with the structural properties of the healing ACL

Alison M Biercevicz  1 , Martha M Murray, Edward G Walsh, Danny L Miranda, Jason T Machan, Braden C Fleming
Affiliations

T2 * MR relaxometry and ligament volume are associated with the structural properties of the healing ACL

Alison M Biercevicz et al. J Orthop Res. 2014 Apr.

Abstract

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 T2 * relaxation time. We also compared our T2 *-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 T2 * maps were established. The structural properties of the ligaments were determined via tensile testing. Using the T2 * histogram profile, each ligament voxel was binned based on its T2 * value into four discrete tissue sub-volumes defined by specific T2 * intervals. The linear combination of the ligament sub-volumes binned by T2 * 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 T2 * 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.

Keywords: ACL; MRI; biomechanics; ligament healing; structural properties.

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Figures

Figure 1
Figure 1
Example ligament histogram showing (A) the bimodal distribution for T2* with associated T2* first quartile (Q1), median (Q2) and third quartile (Q3) summary statistics, (B) the T2* ligament map, and (C) the original DICOM image. Note the ligament voxels illustrated in a red (B) represent voxels with a T2* value of 0 ms. The MR images are a sagittal view of the femoral notch with the femur at the top of the image and the tibia at the bottom. For the MR images shown TE = 7.36 ms.
Figure 2
Figure 2
T2* model: (A) Actual versus predicted maximum load calculated using the linear combination of Vol1, Vol2, Vol3 and Vol4. The dotted lines represent the 95% confidence intervals. Gray shapes represent transected ligaments while black shapes represent repaired ligaments. The highest (star, B), median (square, C) and lowest (hexagon, D) maximum load ligaments and their corresponding histogram profile are also represented with associated T2* first quartile (Q1), median (Q2) and third quartile (Q3) summary statistics.
Figure 3
Figure 3
T2* model: (A) Actual versus predicted yield load (B) and actual versus predicted linear stiffness plots calculated using the linear combination of Vol1, Vol2, Vol3 and Vol4. The dotted lines represent the 95% confidence intervals.
Figure 4
Figure 4
Signal intensity model: (A) Actual versus predicted maximum load calculated using linear combination of VWSI and MGVSI. The dotted lines represent the 95% confidence intervals. Gray shapes represent transected ligaments while black shapes represent repaired ligaments. The highest (star, B), median (square, C) and lowest (hexagon, D) maximum load ligaments and their corresponding histogram profile are also represented with associated SI first quartile (Q1), median (MGVSI, Q2) and third quartile (Q3) summary statistics.
See this image and copyright information in PMC

References

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