PREDICTION OF RHEOLOGICAL MECHANICAL PROPERTIES OF INTERVERTEBRAL DISC USING QUANTITATIVE T2 MR IMAGING METHOD
Institute of Biomedical Engineering, National Taiwan Univsersity, Taiwan
Background: The disc is an anisotropic biphasic organ. The time-dependent behavior may result from interactions between the solid and fluid phase of tissue. The T2 mapping techniques can provide information about the interaction of water and the collagen networks, hence may be an indicator for the biomechanical properties of disc. The purpose of this study is to find the correlation of T2 relaxation time in respect to the rheological and viscoelastic properties of disc.
Materials and Methods: 55 healthy porcine thoracic discs were imaged using a 3T MRI scanner. The T2 relaxation time of NP and AF were acquired. After MRI scanning, discs were dissected for mechanical tests. To find the rheological properties of discs, the creep tests were performed (1 hour 0.8 MPa) and the linear biphasic model was used to find the aggregate modulus and hydraulic permeability. The Dynamic Mechanical Analysis tests were conducted to find the viscoelastic properties. The discs were applied with 0.1~0.8 MPa compressive stress at frequencies from 0.03 to 10Hz. The phase angle of discs was acquired after the test. Pearson correlation was performed to correlate between T2 and disc biomechanical properties. A p-value less than 0.05 was considered to be significant.
Result: Significant correlations were found between the disc permeability and T2 value of NP, but not in AF. No significant correlations were found between the aggregate modulus and T2 values of both NP and AF. The phase angle significantly correlates with the T2 values of AF, particularly at 0.03, 0.1, and 0.3Hz.