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. 2020 Oct;33(5):713-724.
doi: 10.1007/s10334-020-00832-w. Epub 2020 Feb 11.

T2 mapping of the distal sciatic nerve in healthy subjects and patients suffering from lumbar disc herniation with nerve compression

Nico Sollmann  1   2 , Dominik Weidlich  3 , Elisabeth Klupp  4 , Barbara Cervantes  3 , Carl Ganter  3 , Claus Zimmer  4   5 , Ernst J Rummeny  3 , Thomas Baum  4 , Jan S Kirschke  4   5 , Dimitrios C Karampinos  3
Affiliations

T2 mapping of the distal sciatic nerve in healthy subjects and patients suffering from lumbar disc herniation with nerve compression

Nico Sollmann et al. MAGMA. 2020 Oct.

Abstract

Objective: To measure T2 values for magnetic resonance neurography (MRN) of the healthy distal sciatic nerve and compare those to T2 changes in patients with nerve compression.

Materials and methods: Twenty-one healthy subjects and five patients with sciatica due to disc herniation underwent MRN using a T2-prepared turbo spin echo (TSE) sequence of the distal sciatic nerve bilaterally. Six and one of those healthy subjects further underwent a commonly used multi-echo spin-echo (MESE) sequence and magnetic resonance spectroscopy (MRS), respectively.

Results: T2 values derived from the T2-prepared TSE sequence were 44.6 ± 3.0 ms (left) and 44.5 ± 2.6 ms (right) in healthy subjects and showed good inter-reader reliability. In patients, T2 values of 61.5 ± 6.2 ms (affected side) versus 43.3 ± 2.4 ms (unaffected side) were obtained. T2 values of MRS were in good agreement with measurements from the T2-prepared TSE, but not with those of the MESE sequence.

Discussion: A T2-prepared TSE sequence enables precise determination of T2 values of the distal sciatic nerve in agreement with MRS. A MESE sequence tends to overestimate nerve T2 compared to T2 from MRS due to the influence of residual fat on T2 quantification. Our approach may enable to quantitatively assess direct nerve affection related to nerve compression.

Keywords: Magnetic resonance spectroscopy; Peripheral nervous system diseases; Sciatica; Spine.

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Conflict of interest statement

Jan S. Kirschke received speaker honoraria from Philips Healthcare. Dimitrios C. Karampinos received grant support from Philips Healthcare. Nico Sollmann, Dominik Weidlich, Elisabeth Klupp, Barbara Cervantes, Carl Ganter, Claus Zimmer, Ernst J. Rummeny, and Thomas Baum declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
T2 mapping of the distal sciatic nerve and placement of the region of interest (ROI). Representative axial slices of the two-dimensional (2D) T2-weighted DIXON turbo spin echo (TSE) sequence and the T2 map derived from the three-dimensional (3D) T2-prepared TSE sequence in a healthy volunteer (lower thigh region of the left leg). The red arrow points to the lower sciatic nerve in the 2D T2-weighted DIXON TSE sequence (a), the red square encloses the nerve in the T2 map (b). Polygonal ROIs were placed in the three consecutive axial slices depicting the distal sciatic nerve, with ROIs contouring the whole sciatic nerve caliber without the inclusion of surrounding soft tissue or blood vessels (c). The 2D T2-weighted DIXON TSE sequence is scaled with arbitrary units (a.u.), T2 values were extracted in ms. The same approach of ROI placement was followed for the measurements of T2 values in T2 maps derived from a 2D multi-echo spin-echo (MESE) sequence
Fig. 2
Fig. 2
Comparison of T2 maps of the distal sciatic nerve. Comparison between the two-dimensional (2D) T2-weighted DIXON turbo spin echo (TSE) sequence [scaled with arbitrary units (a.u.)], the T2 map derived from the 2D multi-echo spin-echo (MESE) sequence (T2 map MESE), and the T2 map derived from the three-dimensional (3D) T2-prepared TSE sequence (T2 map T2Prep 3D TSE) in a healthy volunteer (lower thigh region of the left leg). Note the higher T2 values (in ms) in the T2 maps of the 2D MESE sequence for structures with fat (particularly the thigh musculature) in comparison to the T2 maps of the 3D T2-prepared TSE sequence
Fig. 3
Fig. 3
T2 values of the distal sciatic nerve. Scatter dot plots with lines indicating means and standard deviation for T2 values (in ms) of the distal sciatic nerve as measured in T2 maps derived from the three-dimensional (3D) T2-prepared turbo spin echo (TSE) sequence and the two-dimensional (2D) multi-echo spin-echo (MESE) sequence. Respective values are separately shown for the left (L) and right (R) distal sciatic nerves
Fig. 4
Fig. 4
T2-weighted raw images and nerve signal decay curves. Comparison of the raw T2-weighted images [scaled with arbitrary units (a.u.)] for the two-dimensional (2D) multi-echo spin-echo (MESE) sequence (upper row) and the three-dimensional (3D) T2-prepared turbo spin echo (TSE) sequence (middle row) in a healthy volunteer (lower thigh region of the left leg). For the 2D MESE sequence, the echo times (TEs) that approximately match the effective T2 weighting times of the 3D T2-prepared TSE sequence are shown. The bottom row shows the acquired spectrum of the distal sciatic nerve (scaled with a.u.). In the right column, the nerve signal decay is shown for the three sequences with the corresponding T2 fit incorporating all available TEs (black dotted line) or matched TEs (green dashed line). When the TEs are matched, a good agreement between magnetic resonance spectroscopy (MRS) and the 3D T2-prepared TSE sequence can be seen, whereas the T2 in the 2D MESE sequence is elevated regardless of TE selection
Fig. 5
Fig. 5
Case series of patients. Sagittal and axial slices of structural magnetic resonance imaging (MRI) from a case series of five patients with unilateral sciatica due to degenerative disc disease with disc herniation and unilateral nerve contact of degenerated disc material (red circles). Furthermore, representative axial T2 maps derived from the three-dimensional (3D) T2-prepared turbo spin echo (TSE) sequence are shown for the right and left lower thigh regions, depicting the distal sciatic nerve (white squares). Mean ± standard deviation of measured T2 values of the lower sciatic nerve was 61.5 ± 6.2 ms for the affected side and 43.3 ± 2.4 ms for the contralateral, unaffected side
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