Sodium MR imaging of the lumbar intervertebral disk at 7 T: Correlation with T2 mapping and modified Pfirrmann score at 3 T - Preliminary results

Purpose: To compare sodium imaging of lumbar intervertebral disks in asymptomatic volunteers at 7-T magnetic resonance (MR) imaging with quantitative T2 mapping and morphologic scoring at 3 T. Materials and Methods: Following ethical board approval and informed consent, the L2-3 to L5-S1 disks were examined in 10 asymptomatic volunteers (nine men, one woman; mean age, 30 years; range, 23-43 years). At 7 T, normalized sodium signal-to-noise ratios were calculated, by using region-of-interest analysis. At 3 T, T2 mapping was performed with a multiecho spin-echo sequence (repetition time msec/echo times msec, 1500/24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156). T2 values were calculated over the nucleus, with a pixelwise, monoexponential nonnegative least-squares-fit analysis. Morphologic grading according to a modified Pfirrmann score was assessed independently by three experienced musculoskeletal radiologists, and Pearson correlation analysis of the covariates was performed. Results: The mean normalized sodium signal intensity was 275.5 ± 115.4 (standard deviation). The T2 mapping showed a mean value of 89.8 msec ± 19.34. The median modified Pfirrmann score was 2b (90% had score ≤ 3c). The Pearson correlation coefficient showed a cubic function between sodium imaging and the modified Pfirrmann score, a moderate inverse correlation between T2 mapping and the modified Pfirrmann score (r = 20.62), and no correlation between sodium imaging and T2 mapping (r = 0.06). Conclusion: The results suggest that MR imaging of the intervertebral disk, using sodium imaging and T2 mapping, can help characterize different component changes and that both of these methods are to some degree related to the Pfirrmann score.