Assessing Intervertebral Disk Tissue Mechanics Using Dual-Actuator Multifrequency Magnetic Resonance Elastography: Case Reports.

Degenerative disk disease (DDD) is a progressive condition that occurs when the intervertebral discs (IVDs), which act as shock absorbers between the vertebrae, degenerate or wear out. Due to this degeneration process, the mechanical properties of the IVD, providing flexibility between adjacent vertebrae, can change. Thus, assessing these mechanical properties may improve diagnosis and treatment guidance for DDD. In this article, we tested in vivo multifrequency magnetic resonance elastography (MMRE) of the human IVD in identifying progressively DDD in three asymptomatic male volunteers aged 32, 50, and 60 years. MMRE of the lumbar spine was acquired using a dual-actuator setup and operated at four frequencies from 60 to 90 Hz. MMRE data were postprocessed using multifrequency wave-number recovery (k-MDEV) inversion algorithm. The resulting shear wave speed (SWS) values were used as a surrogate parameter of tissue stiffness and then compared to Pfirrmann grading (Pf) of disc degeneration (1-5) performed by an experienced MRI spine researcher. Morphological Pf demonstrated an inverse relationship between increasing IVD stiffness and progressive IVD degeneration by a Spearman's rank correlation coefficient of  = -0.792, < 0.001. MMRE allows measurement of in vivo mechanical properties of IVDs and may provide additional information in disc degeneration beyond standard morphological changes. Prior to the clinical use of this technique, future studies should be conducted to evaluate the reproducibility and repeatability of spinal MMRE in the spine, and particularly its potential confounders.