4835
Elastic modulus of acetabular labrum correlates with UTE apparent spin-spin (T2*) and spin-lattice (T1) magnetic resonance relaxation times
Dina Moazamian1, Takehito Hananouchi2,3, Hamidreza Shaterian Mohammadi1, Arya Suprana1, Alireza Tayarani4, Erik W Dorthe3, Darryl W D’Lima3, Yajun Ma5, and Saeed Jerban5
1Radiology, University of California San Diego, San Diego, CA, United States, 2Academia-Government-Industry Collaboration, Office of Research and Academia-Government-Community Collaboration Hiroshima University, Hiroshima, Japan, 3Orthopedic, Shiley Center for Orthopedic Research and Education at Scripps Clinic, San Diego, CA, United States, 4Pathology, University of California San Diego, San Diego, CA, United States, 5Radiology, Radiology, University of California San Diego, San Diego, CA, United States, San Diego, CA, United States
1Radiology, University of California San Diego, San Diego, CA, United States, 2Academia-Government-Industry Collaboration, Office of Research and Academia-Government-Community Collaboration Hiroshima University, Hiroshima, Japan, 3Orthopedic, Shiley Center for Orthopedic Research and Education at Scripps Clinic, San Diego, CA, United States, 4Pathology, University of California San Diego, San Diego, CA, United States, 5Radiology, Radiology, University of California San Diego, San Diego, CA, United States, San Diego, CA, United States
Synopsis
Keywords: High-Field MRI, Cartilage, Acetabular Labrum, UTE
Motivation: The acetabulum labrum plays a critical role in the hip function. Medical imaging techniques for detecting labral degeneration may help improve our knowledge of its role in hip osteoarthritis (OA).
Goal(s): This study aimed to explore the correlation between the mechanical properties of the acetabulum labrum and MRI properties.
Approach: The correlations of UTE-T2* and -T1 sequences with the tensile elastic modulus of human acetabular labrum specimens have been investigated.
Results: There was a significant correlation between quantitative UTE-T2*, and UTE-T1 techniques and the mechanical properties of the labrum.
Impact: UTE-T2* and -T1 sequences showed the potential to evaluate acetabulum labrum mechanical assessment, which is needed to improve labrum degeneration detection and monitoring, a primary unmet need in areas where hip osteoarthritis is common and conventional MRI is being implemented.
Background
The acetabular labrum is a C-shaped fibrocartilaginous rim that outlines the bony acetabulum’s ring in the hip joint 1. It is crucial in maintaining normal hip joint biomechanics and function 2,3.Labral damage can lead to abnormal joint mechanics, increasing the risk of osteoarthritis (OA) 7–9. Therefore, a non-invasive assessment of the labrum quality and its mechanical status may help detect OA-related changes in the hip joint.
The labrum appears dark on conventional T1- and T2-weighted MR images due to its short spin-spin (T2) relaxation time 11,12. Therefore, employing ultrashort echo time (UTE) MRI sequences may be suitable for quantitative labrum imaging. Apparent spin-spin (T2*) and Spin-lattice (T1) relaxation times are common quantitative MRI techniques used for musculoskeletal tissue evaluation 13,14, which have been investigated in this study.
Methods
Acetabular labrum specimens were dissected from 12 fresh-frozen human cadaveric hip joints (64.6±11.6 years old at the time of death, 7 female). All specimens were placed separately in 5-ML syringes for MR imaging (Fig 1A-B). The dissected acetabular labrum specimens were soaked in phosphate-buffered saline for 1 hour before scanning. All syringes were filled with perfluoropolyether (Fomblin, Ausimont, USA) to minimize dehydration and susceptibility artifacts during MRI scans.The UTE-MRI scans were performed on a 3T MRI scanner (MR750, GE Healthcare Technologies, USA) using a standard 8 channels transmit/receive knee coil. All MRI images were acquired in the axial plane. Two following sets of 3D UTE Cones MRI sequences were performed, 1) 3D UTE Cones T2* sequence with multiple TEs to measure T2* values and 2) actual flip angle (FA) sequences with variable FA (AFA-VFA)-based 3D UTE Cones to measure T1 values 15. Data acquisition parameters for the two quantitative UTE-MRI protocols are presented in Table 1.
UTE-MRI biomarkers were calculated in three representative slices at the middle of each specimen (volume of interest (VOI) is indicated in Figure 1A) within global regions of interest (ROIs) covering the entire cross-sectional area. For each slice, average signal values within the ROI were used for T2* and T1 measurements using single-component exponential fitting models developed in MATLAB (The Mathworks Inc., Natick, USA).
The stiffness and the elastic modulus (E) of the specimens were measured before MRI scans. The mechanical setup with a representative-mounted acetabular labrum specimen is shown in Figure 1C. Both ends of the specimens were mounted on the stainless-steel grippers of an in-house developed benchtop uniaxial loading device. The initial distance between the fixed and actuated gripper was set to 10 mm. After initial alignment and 0.02 newton (N) preloading to straighten the specimens, a 1-mm tensile displacement (maximum strain = 0.1 N) was applied at a 0.3 mm/sec rate, and the applied force was recorded. The average maximum stiffness and stress were calculated as the maximum force divided by the tissue’s effective length (10 mm) and cross-sectional area, respectively. The average tensile elastic modulus was calculated as the average maximum stress divided by the average maximum strain.
The Spearman’s rank correlations were calculated between average UTE-MRI quantifications and the acetabular labrum mechanical properties. Statistical analyses were performed in SPSS. P values below 0.05 were considered significant.
Results
Figure 2 shows single-component exponential T2* and T1 fittings for a representative human acetabular labrum specimen (from a 68-year-old male donor). The high signal obtained by UTE MRI leads to a well-fitting of the actual data points.Table 2 summarizes the mean, standard deviation (SD) of the age, BMI, and UTE-T2* and -T1 values and mechanical properties in the studied acetabular labrum specimens.
Figure 3 shows the scatter plots, linear regression trendlines, and Spearman’s rank correlation coefficients of the elastic modulus and stiffness on UTE-T2* and UTE-T1 techniques. Elastic modulus showed a significant inverse correlation with UTE-T2* (R=-0.66, P<0.01) and with UTE-T1 (R=-0.56, P=0.05). The stiffness of the specimens showed significant inverse correlations with UTE-T2* (R=-0.53, P=0.01) and UTE-T1 (R=-0.63, P=0.02).
Conclusion
Mechanical properties of the acetabular labrums showed significant inverse correlations with UTE-T2* and UTE-T1. This study highlighted the potential of UTE-MRI techniques for the acetabular labrum mechanical assessment which can help improve labrum degeneration detection and monitoring which requires further investigations.Acknowledgements
The authors acknowledge grant support from NIH (K01AR080257, R01AR079484) and JSPS KAKENHI (JP19K09658, JP18KK0104).References
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Figures
Table1.
Data acquisition parameters for quantitative UTE-MRI protocols.
Table 2. Average, standard deviation, and range of the UTE-MRI, mechanical in the studied labrum specimens.
Figure 1: (A) A representative fresh hip labrum specimen harvested from the hip
joint of a 60-year-old female. The middle third of the specimen is highlighted
as the volume interest region (VOI) analyzed in MRI. (B) Each hip labrum
specimen was placed in a standard 5-ml syringe filled with Fomblin. (C) hip
labrum specimen mounted on the grippers of the in-house developed benchtop
uniaxial loading device for mechanical tensile tests.
Figure 2: Quantitative UTE-MRI analyses in a representative human Labrum specimen (from a 68-year-old male donor). (A) selected region of interest (ROI) for the same sample depicted schematically on the UTE-MRI image. (B) Single-component exponential fitting of T2* decay, (C) T1 recovery
Figure 3: Scatter plot and linear regressions of mechanical characteristics on quantitative UTE-MRI analyses in human Labrum specimen. (A, B) T2* (ms) values which showed a significant inverse correlation with Young Modulus (Mpa) and Stiffness (N/mm) of the hip labrum, respectively, (C, D) T1 (ms) values with a significant inverse correlation with Young Modulus (Mpa) and Stiffness (N/mm) of the hip labrum, respectively. Significance levels for these correlations were below 0.05.
DOI: https://doi.org/10.58530/2024/4835