ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

The total length of the segment describing the intervertebral disc was adapted to the
anatomy of each investigated disc, based on MRI assessment. As boundary condition, a
logarithmic function approximating the T1 relative signal enhancement determined by
contrast-enhanced MRI was assigned to the cranial and caudal BEPs. Diffusion
response was assumed to be dominated by the CEPs; therefore, diffusion coefficients of
vertebral bone, BEPs and nucleus pulposus were assumed to be fixed.
The diffusion coefficients of the two CEPs were optimized in order to minimize the sum
of the differences between the predicted T1 signal enhancement inside the intervertebral
disc and the CEPs and the actual T1 signal enhancement determined by MRI
acquisitions. The NOMAD open source package (5) was used for the optimization;
simulations were carried out in ABAQUS 6.10 (SIMULIA, Providence, RI, USA)
driven by a purposely developed Python script.
4. RESULTS
Figure 2 shows the average T1 signal enhancement profiles obtained 5 minutes, 10
minutes, 2, 4 and 6 hours after injection of the contrast agent in the 68 discs.
Figure 2. Average profiles of the relative T1 signal enhancement measured at different
time points
At 5 minutes, the contrast agent concentration is maximal in the bony regions close to
the endplates, due to the blood supply (Fig. 3). With progressing time, the contrast agent
diffuses first into the CEPs and then into the intervertebral disc, reaching the peak in the
centre of the disc 6 hours after injection. By this time, its concentration into blood and
therefore into vertebral bone decreases to negligible values.