Non-invasive quantification of age-related changes in the vertebral endplate in rats using in vivo DCE-MRI

Abstract

Background: Small animal models that can mimic degenerative disc disease (DDD) are commonly used to examine DDD progression. However, assessments such as histological studies and macroscopic measurements do not allow for longitudinal studies because they can only be completed after the animal is sacrificed. Dynamic contrast-enhanced MRI (DCE-MRI) may provide a reliable, non-invasive in vivo method for detecting the progression.

Methods: The present study investigated the progression of changes in lumbar discs and the effect of endplate conditions on diffusion into the lumbar discs of aging sand rats after intravenous administration of gadolinium-containing contrast medium through the tail vein. Contrast enhancement was measured in the lumbar intervertebral discs on each image. The results were compared with those from conventional histological characterizations.

Results: T2-weighted images revealed that with aging, the shape of L3-L4, L4-L5, L5-L6, and L6-S1 nucleus pulposus (NP) became irregular, while the mean areas, signal intensities, and T2 values of the NP were significantly decreased. Each of the observed disc changes demonstrated a progressive increase in phase during 2-min scout scans. Post-contrast MRI showed impaired endplate nutritional diffusion to the disc with aging, enhancement was significantly greater in young animals than in old animals. Endplate calcification or sclerosis was histologically confirmed; histologic score was correlated with the age. We found the histological score of the endplate negatively corresponded to the DCE-MRI results.

Conclusions: DCE-MRI studies offer a non-invasive in vivo method for investigating the progress of diffusion into the discs and the functional conditions of the endplate. We conclude that quantitative DCE-MRI can identify the severity of disc degeneration and efficiently reflect the progression of vertebral endplate changes in the aging sand rat lumbar spine via the NP contrast enhancement patterns.

Keywords: Degenerative disc disease; Dynamic contrast-enhanced magnetic resonance imaging; Intervertebral disc endplate; Lumbar spine.

Fig. 1

Computer screen captures showing a raw, T2-weighted magnetic resonance image of a rat lumbar spine (a) and the same image with NP outlined to define ROI (b).The measured NP area and signal intensity are shown (L3–L4 represent the intervertebral disc between the third and the fourth lumbar vertebra, and so on)

Fig. 2

The nucleus pulposus area in different levels of the T2-weighted magnetic resonance images. *Indicates significant differences between different months, P < 0.05. No significant differences were observed in the intervertebral discs of different levels between 6- and 9-month-old groups (L3–L4 represent the intervertebral disc between the third and the fourth lumbar vertebra, and so on)

Fig. 3

The signal intensity of the nucleus pulposus in different levels of the T2-weighted magnetic resonance images. *Indicates significant differences between different months, P < 0.05. No significant differences were observed in the intervertebral discs of different levels between 6- and 9-month-old groups (L3–L4 represent the intervertebral disc between the third and the fourth lumbar vertebra, and so on)

Fig. 4

Measured T2 values from regions of interest (ROIs) in the nucleus pulposus plotted over the L3–L4 to L6–S1 disc levels from sagittal mid-axial images of rats of different ages. Comparison of T2 values between the different lumbar levels revealed differences statistically with age (P < 0.05, respectively) (L3–L4 represent the intervertebral disc between the third and the fourth lumbar vertebra, and so on)

Fig. 5

Sagittal T2-weighted images (gray images) and corresponding T2 maps (colored images) of discs with different levels. Relaxation times (ms) are displayed on the right of each T2 map image. a Intervertebral disc in L3–L4. b Intervertebral disc in L4–L5. c Intervertebral disc in L5–L6. d Intervertebral disc in L6–S1

Fig. 6

Dynamic MRI enhancement curve of different lumbar levels in different ages. Disc enhancement patterns show progressive increase within 2 min. Similar enhancement curve is seen in lumbar levels with different ages (L3–L4 represent the intervertebral disc between the third and the fourth lumbar vertebra, and so on)

Fig. 7

Representative histologic sections (H&E staining) of the disc and endplate (original magnification, ×10). a Young group. b Middle-aged group. c Old group. With aging, rats show loss of cellularity in the endplate, and the articular cartilage undergoes endochondral ossification and is replaced by bone

Fig. 8

Representative histologic sections (Safranin O/Fast Green stain) of the disc and endplate (original magnification, ×10). a Young group. b Middle-aged group. c Old group. With aging, the concentration of sulfated glycosaminoglycans (sGAG, arrows) was decreased and resorption of the articular cartilage was replaced by bone in the endplate