Magnetic Resonance Elastography for Mechanical Modeling of the Human Lumbar Intervertebral Disc.

Magnetic Resonance Elastography (MRE) is a phase-contrast imaging technique that allows for determination of mechanical properties of tissue in-vivo. Due to physiological and morphological changes leading to changes in tissue mechanical properties, MRE may be a promising imaging tool for detection of intervertebral disc degeneration. We therefore performed a preliminary study to determine the frequency dependent mechanical properties of the lumbar intervertebral discs. Six healthy volunteers underwent multifrequency MRE (50, 80, and 100 Hz) to measure the mechanical properties of the intervertebral discs between the L3 and L4, and L4 and L5 vertebrae. Frequency-independent disc mechanical properties and best-fit mechanical model were determined from the frequency-dependent disc data by comparing four different linear viscoelastic material models (Maxwell, Kelvin-Voigt, Springpot, and Zener). A seventh individual with a history of a discectomy on the disc between the L4 and L5 vertebrae was also scanned to provide a preliminary analysis about how degeneration impacts disc mechanical properties. Our findings show that the Zener model may best represent the disc's frequency-dependent mechanical response. Additionally, we observed a significantly lower complex shear modulus in the degenerated disc than the healthy discs at each frequency, demonstrating the potential for MRE to detect early signs of degeneration and pinpoint the cause of chronic back pain.