Objective: To analyze the relationship between the bone mineral density (BMD) and lumbar intervertebral disc degeneration in rhesus macaques by using T1ρ-MRI.
Methods: Twenty female rhesus macaques at the age of 10.9 years on average (rang, 4-20 years) were selected. The lumbar intervertebral discs were classified by Pfirrmann grading system and the T1ρ relaxation time (T1ρ value) was examined by using MRI (Philips 1.5 Tesla), and then BMD values of the L4,5 vertebrae and femoral ward's triangle were detected by using Osteocore dual energy X-ray absorptiometry. Finally, the relationship of T1ρ value of the lumbar intervertebral discs and Pfirrmann grading with age, weight, BMD of lumbar vertebrae and femoral ward's triangle was analyzed.
Results: The BMD values of lumbar vertebrae and femoral ward's triangle were (0.64 ± 0.17) g/cm2 and (0.67 ± 0.19) g/cm2 respectively, showing no significant difference (t = 2.893, P = 0.128). According to Pfirrmann grading system, there were 7 cases of grade I, 8 cases of grade II, and 5 cases of grade III at L4,5 intervertebral discs. The T1ρ value of the lumbar intervertebral disc was (104.08 ± 18.65) ms; the T1ρ values of grades I, II, and III were (121.31 ± 13.44), (104.73 ± 15.01), and (77.41 ± 11.87) ms, respectively. There was a negative correlation between T1ρ value and the age and the BMD of lumbar vertebrae and femoral ward's triangle. There was a positive correlation between Pfirrmann grading and the variables as listed above. Significant negative linear correlation was also observed between T1ρ value and Pfirrmann grading.
Conclusion: The T1ρ value is a reliable index when quantifying lumbar intervertebral disc degeneration, and there is a significant positive correlation between BMD and lumbar intervertebral disc degeneration in rhesus macaques.