100 patients presenting with complaint of low back pain were examined, of which 49 patients were male and 51 female (figure 5).
A total of 494 discs were examined of 100 patients, 5 discs from each patient from L1-L2 to L5-S1. Sacralisation of L5 vertebral body was noted in 6 patients.
According to the Pfirrmann grading system, 70 discs (14%) were classified as grade I, 130 discs (26%) as grade II, 134 discs (27%) as grade III, 145 discs (30%) as grade IV and 15 discs (5%) had a collapsed disc space (grade V) [figure 6]. Of these, the collapsed disc spaces (grade V) were excluded from T2 mapping measurements due to insufficient space to place ROIs. As such, 479 intervertebral discs served as study sample in order to obtain normative T2 values.
The mean T2 values for all lumbar disc levels for nucleus pulposus were 210.14 ± 32.19 ms (mean ± standard deviation) for grade I, 128.99 ± 18.64 ms for grade II, 84.1 ± 10.34 ms for grade III and 51.2 ± 9.29 ms for grade IV. There was a significant stepwise decrease in NP T2 values from grade I to grade IV, with highly significant differences between each grade (all p < 0.001; figure 7 and 8).
The mean T2 values for all lumbar disc levels for annulus fibrosus anterior fibers were 54.76 ± 6.27 ms (mean ± standard deviation) for grade I, 49.99 ± 5.72 ms for grade II, 45.29 ± 5.05 ms for grade III and 36.74 ± 6.31 ms for grade IV (figure 7).
The mean T2 values for all lumbar disc levels for annulus fibrosus posterior fibers were 61.97 ± 7.02 ms (mean ± standard deviation) for grade I, 53.83 ± 5.8 ms for grade II, 48.2 ± 6.26 ms for grade III and 39.51 ± 5.55 ms for grade IV (figure 7).
Similar mild decrease in AF anterior and posterior T2 values from grade I to grade IV is noted with highly significant differences between each grade (p < 0.0001; figure 9 and 10).
The graphical representation of the mean T2 relaxation values (in milliseconds, ms) of anterior AF fibres, NP as well as posterior AF fibres for all lumbar intervertebral disc levels for different Pfirrmann grades is summarised in figure 7 and graphed in figure 11.
The representative cases with Pfirrmann morphological grading and T2 mapping at respective lumbar discs is shown in figure 12, 13 and 14.
The limitations of this study includes the lack of a gold standard to confirm or classify the degeneration and no standard values for Indian population. A multi-centric approach with a larger cohort of symptomatic patients as well as asymptomatic population will be beneficial in attaining a normal/normative data. Secondly, inter-observer and diurnal variation has not been assessed in this study. Thirdly, morphological grading might change from centre to centre with MRI at different field strengths due to variations in image quality.