Study Design. Animal experimental study.
Objective. To evaluate a novel quantitative imaging technique for assessing disc degeneration.
Summary of Background Data. T2-relaxation time (T2-RT) measurements have been used to assess disc degeneration quanti-tatively. T2 values correlate with the water content of intervertebral disc tissue and thereby allow for the indirect measurement of nucleus pulposus (NP) hydration.
Methods. We developed an algorithm to subtract out magnetic resonance imaging (MRI) voxels not representing NP tissue on the basis of T2-RT values. Filtered NP voxels were used to measure nuclear size by their amount and nuclear hydration by their mean T2-RT. This technique was applied to 24 rat-tail intervertebral discs (IVDs), which had been punctured with an 18-gauge needle according to different techniques to induce varying degrees of degeneration. NP voxel count and average T2-RT were used as parameters to assess the degeneration process at 1 and 3 months postpuncture. NP voxel counts were evaluated against radiograph disc height measurements and qualitative MRI studies on the basis of the Pfirrmann grading system. Tails were collected for histology to correlate NP voxel counts to histological disc degeneration grades and to NP cross-sectional area measurements.
Results. NP voxel count measurements showed strong correlations to qualitative MRI analyses (R2 = 0.79, P < 0.0001), histological degeneration grades (R2 = 0.902, P < 0.0001), and histological NP cross-sectional area measurements (R2 = 0.887, P < 0.0001).
In contrast to NP voxel counts, the mean T2-RT for each punctured group remained constant between months 1 and 3. The mean T2-RTs for the punctured groups did not show a statistically significant difference from those of healthy IVDs (63.55 ms ± 5.88 ms mo 1 and 62.61 ms ± 5.02 ms) at either time point.
Conclusion. The NP voxel count proved to be a valid parameter to assess disc degeneration quantitatively in a needle puncture model. The mean NP T2-RT does not change significantly in needle-puncture–induced degenerated IVDs. IVDs can be segmented into different tissue components according to their innate T2-RT.
Level of Evidence: N/A
A magnetic resonance imaging measurement technique developed to quantitatively assess intervertebral disc degeneration. The method is based on T2-relaxation time measurements allowing us to quantify the size and hydration of the nucleus pulposus. The viability of this technique was evaluated in a needle puncture rat-tail model. This technique allowed us to establish a sensitive and continuous scale of disc degeneration that correlates to other established disc degeneration assessments.
*Weill Cornell Brain and Spine Institute, Department of Neurological Surgery, Weill Cornell Medical College, NYPH, New York, NY
†Department of Biomedical Engineering, Cornell University, Ithaca, NY
‡Citigroup Biomedical Imaging Center, Weill Cornell Medical College, New York, NY; and
§Department of Radiology, Weill Cornell Medical College, New York, NY.
Address correspondence and reprint requests to Roger Härtl, MD, Weill Cornell Brain and Spine Institute, Department of Neurological Surgery, Weill Cornell Medical College, NYPH, 525 East 68th St, Box 99, New York, NY 10065; E-mail: firstname.lastname@example.org
Acknowledgment date: April 2, 2013. First revision date: September 14, 2013. Second revision date: October 17, 2013. Acceptance date: October 22, 2013.
The manuscript submitted does not contain information about medical device(s)/drug(s).
AOSpine, AOSpine International, HHMI, NFL, and NIH grant funds were received to support this work.
Relevant financial activities outside the submitted work: employment, consultancy, expert testimony, grants.