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Intervertebral Disc Elastography to Relate Shear Modulus and Relaxometry in Compression and Bending.
Zachary R Davis1, Paull C Gossett1, Robert L Wilson2
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA.
Biorxiv : the Preprint Server for Biology
|September 21, 2023
Summary
This study explored MRI-based methods to assess intervertebral disc degeneration. Findings suggest strain imaging and relaxometry can serve as biomarkers for disc health and function.
Area of Science:
- Biomedical Engineering
- Radiology
- Orthopedics
Background:
- Intervertebral disc degeneration is a primary cause of low back pain, involving tissue structural and mechanical decline.
- Current assessment methods for disc degeneration lack ideal measures of function, such as mechanical parameters like strain and stiffness.
- The predictive capability of MRI relaxometry (T1 and T2) for disc strain and stiffness remains largely unknown.
Purpose of the Study:
- To quantify T1 and T2 relaxation times and in-plane strains using displacement-encoded MRI.
- To estimate shear modulus and compare it with relaxation times and strains under compression and bending.
- To investigate the potential of MRI-based elastography and relaxometry as biomarkers for disc degeneration.
Main Methods:
- Displacement-encoded MRI was used to measure T1 and T2 relaxation times and in-plane strains in the intervertebral disc.
- Physiological compression and bending loads were applied to the disc during imaging.
- Shear modulus was estimated in orthogonal planes and correlated with MRI relaxation times and strain measurements.
Main Results:
- Intratissue strain varied with loading mode (compression vs. bending).
- Nucleus pulposus shear modulus was significantly lower than annulus fibrosus, except under bending, where stiffness was load-dependent.
- Correlation between shear moduli estimated from compression and bending was poor, highlighting the need for multi-modal loading in future models.
Conclusions:
- Strain imaging and strain-based material property estimation can serve as imaging biomarkers to differentiate healthy from degenerated discs.
- Image-based elastography and relaxometry offer complementary assessments of disc structure and function for longitudinal degeneration studies.
- Future inverse models for disc mechanics should integrate data from multiple loading conditions for improved accuracy.
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