Nucleus pulposus structure and function assessed in shear using magnetic resonance elastography, quantitative MRI,...

Area of Science:

• Biomedical Engineering
• Quantitative Imaging
• Musculoskeletal Research

Background:

• Quantitative MRI and Magnetic Resonance Elastography (MRE) offer in vivo assessment of intervertebral disc (IVD) structure-function.
• MRE measures tissue shear properties, complementing quantitative MRI metrics for IVD composition analysis.
• Understanding the IVD's structure-function relationship is crucial for disease stratification and evaluating restorative therapies.

Purpose of the Study:

• Compare MRE-derived and rheometry-derived shear modulus in agarose gels and nucleus pulposus (NP) tissue.
• Correlate MRE and rheological measures of NP tissue with biochemical composition and quantitative MRI parameters.
• Validate MRE as a tool for assessing IVD mechanical properties and their relationship to tissue composition.

Main Methods:

• Agarose gels and bovine caudal IVDs were assessed using MRE and MRI (T1ρ and T2 mapping).
• Torsional mechanical testing (frequency sweep 1-100 Hz) and creep/stress relaxation tests were performed on NP tissue.
• Linear mixed-effects models and regression analyses were used to evaluate testing methods, sample properties, and correlations.

Main Results:

• Shear moduli increased with frequency (100 Hz > 80 Hz) for both MRE and rheometry in all samples.
• Lower water content correlated with higher complex shear moduli.
• T1ρ and T2 relaxation times negatively correlated with complex shear modulus; NP tissue shear modulus positively correlated with GAG/wet-weight and negatively with water content.

Conclusions:

• MRE effectively assesses hydration-induced changes in IVD shear properties.
• This study highlights the structure-function relationship between NP tissue composition and its mechanical behavior.
• MRE shows promise for non-invasively evaluating IVD health and therapeutic responses.