Value of chemical shift imaging in the evaluation of neural foramen stenosis

Abstract

Background: Chemical shift Magnetic Resonance Imaging (MRI) is often routinely acquired to assess a spectrum of spinal lesions due to its ability versatility to obtain rapid sequences at the expense of spatial resolution images. It is one of the quickest sequences to acquire at the expense of spatial resolution.

Objective: In this study we assess the diagnostic efficacy of Chemical shift Magnetic Resonance Imaging (MRI) in the evaluation of Neural Foraminal stenosis.

Materials and methods: Conventional T2, T1 and STIR sagittal and axial images as well as 'in' and 'out' phase chemical shift sagittal MRI sequences of 25 consecutive patients presenting with back pain and radiculopathy were reviewed. The degree of neural stenosis in the lumbar spine foramina on both sides was graded using the Lee classification on T2 and 'in' and 'out' phase MRI sequences by two independent MSK radiologists. Statistical analysis was performed using paired T-Test and Cohen's weighted kappa test was applied as a measure of agreement between the two observed raters.

Results: A total of 250 lumbar neural foramina were assessed. There was substantial agreement (Cohen's weighted kappa) for both raters between 'in' and 'out' phase chemical shift sagittal MRI sequences (rater 1 = 0.699, rater 2 = 0.718), as well as good agreement between raters for both 'in' and 'out' phase chemical shift sagittal MRI sequences (in phase = 0.656, 'out' phase = 0.576). However, when compared to the gold standard rating on a T2 based sequence, ratings on in' and 'out' phase MRI sequences overestimated the degree of stenosis. When comparing 'in' and 'out' ratings to the T2 ratings, agreement was poor with kappa ranging from 0.132 to 0.202.

Conclusion: Though both 'in' and 'out' phase chemical shift sagittal MRI sequences can be used to analyse neural foraminal stenosis, given its propensity to over-estimate the degree of stenosis in comparison to the T2 based images, assessment of the condition on these complementary limited sequences technique should be avoided/should be undertaken with caution.

Keywords: Chemical shift; Lumbar vertebrae; Magnetic resonance imaging; Neuroforaminal stenosis; Radiculopathy.

Fig. 1

Chemical shift in phase (a) and out phase (b) and T2 sagittal (c) showing neural foramen which are patent.(short arrows) Note the apparent narrowing of neural foramen (long arrow) on out phase but patent on in phase and T2.

Fig. 2

Chemical shift in phase (a) and out phase (b) and T2 sagittal (c) showing apparent narrowing of neural foramen (arrow) on in phase and out phase but patent on T2.

Fig. 3

Chemical shift in phase (a) and out phase (b) and T2 sagittal (c) showing apparent narrowing of neural foramen (arrow) on out phase but patent on in phase and T2.

Fig. 4

Average ratings of values on in phase, out phase and T2. SD- Standard deviation.

Fig. 5

Comparison of Kappa values for both raters for in vs out of phase, in-phase vs T2, out-phase vs T2. T2 refers to the gold-standard "answer" stenosis rating as determinated on T2 weighted sequences.