Abstract

Plots of differences of T2 time in milliseconds (y-axis) of 604 lumbar IVDs with Pfirrmann grades of ≤2 (blue), 3 (red), and 4 (green) relative to mean T2 time (or T2 time when single) of other healthy lumbar IVDs from same individual (I), all other healthy IVDs in 101 study participants without (X) and with (Xs) stratification for the segmental level, 6 randomly selected healthy IVDs representing T12–S1 segments (Xc), and a single randomly selected IVD from same segmental levels (Xcs). Horizontal bars show means with standard errors. The variation in T2 times of healthy IVDs, as represented by the spread along the y-axis, is least for healthy IVDs with Pfirrmann grade of ≤2. Notice that the measure I provides the most and the measure Xcs provides the least discrimination between healthy and degenerated IVDs with Pfirrmann grades of 3 or 4, as indicated by separation of means along the y-axis.

BACKGROUND AND PURPOSE

When one uses T2 relaxometry to classify lumbar intervertebral discs as degenerated, it is unclear whether the normative data should be based on other intervertebral discs from the same individual or from a pool of extraneous controls. This study aimed to explore the extent of intra- versus intersubject variation in the T2 times of healthy intervertebral discs.

MATERIALS AND METHODS

Using prospectively acquired T2-relaxometry data from 606 intervertebral discs in 101 volunteers without back pain (47 men, 54 women) in a narrow age range (25–35 years), we calculated intra- and intersubject variation in T2 times of intervertebral discs graded by 2 neuroradiologists on the Pfirrmann scale. Intrasubject variation of intervertebral discs was assessed relative to other healthy intervertebral discs (Pfirrmann grade, ≤2) in the same individual. Multiple intersubject variability measures were calculated using healthy extraneous references ranging from a single randomly selected intervertebral disc to all healthy extraneous intervertebral discs, without and with segmental stratification. These variability measures were compared for healthy and degenerated (Pfirrmann grade ≥3) intervertebral discs.

RESULTS

The mean T2 values of healthy (493/606, 81.3%) and degenerated intervertebral discs were 121.1 ± 22.5 ms and 91.5 ± 18.6 ms, respectively (P < .001). The mean intrasubject variability for healthy intervertebral discs was 9.8 ± 10.7 ms, lower than all intersubject variability measures (P < .001), and provided the most pronounced separation for healthy and degenerated intervertebral discs. Among intersubject variability measures, using all segment-matched healthy discs as references provided the lowest variability (P < .001).

CONCLUSIONS

Normative measures based on the T2 times of healthy intervertebral discs from the same individual are likely to provide the most discriminating means of identifying degenerated intervertebral discs on the basis of T2 relaxometry.

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jross

Jeffrey Ross

• Mayo Clinic, Phoenix

Dr. Jeffrey S. Ross is a Professor of Radiology at the Mayo Clinic College of Medicine, and practices neuroradiology at the Mayo Clinic in Phoenix, Arizona. His publications include over 100 peer-reviewed articles, nearly 60 non-refereed articles, 33 book chapters, and 10 books. He was an AJNR Senior Editor from 2006-2015, is a member of the editorial board for 3 other journals, and a manuscript reviewer for 10 journals. He became Editor-in-Chief of the AJNR in July 2015. He received the Gold Medal Award from the ASSR in 2013.



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