Delineation of Inner Annulus Fibrosus and Nucleus Pulposus on Routine T2-weighted MR Images

Study design: Retrospective study of 150 IVDs.

Objective: Assessment of costume algorithm ability to delineate the IAF and NP on routine T2 images.

Summary of background data: Central hyperintense region on T2-weighted MR images of normal lumbar IVDs represents a combination of IAF and NP. Ability to identify NP as distinct from IAF can help improve our understanding of IVD morphology in-vivo.

Methods: Sagittal T2-weighted TSE MR images of 150 lumbar IVDs from 25 patients were analyzed. MR images were processed using a custom algorithm that markedly increased the signal intensity of structures with inherent signal intensity within 2 defined intensity thresholds. Signal intensity and contrast-to- noise ratio between outer annulus fibrosus, IAF, and NP were assessed at baseline and after processing. To assess consistency of underlying T2 differences, similar analysis was done on 108 discs from 18 patients in whom additional sagittal T2-weighted STIR images were available.

Results: Following image processing, apparent IAF and NP were rendered visible in 86% and 84.3% IVDs on T2-weighted TSE and STIR images respectively. While signal intensity of these 2 regions was inherently different (P< 0.001) before processing on TSE and STIR images, their visualization was facilitated by a significant increase (P<0.001) in contrast-to-noise ratio after processing. Nonvisualization of NP was associated with disc degeneration (P<0.001).

Conclusion: Inherent differences exist in signal intensities of normal NP and IAF on T2-weighted MR images. Accentuating these differences using image postprocessing techniques can render these 2 structures visible.