Abstract
PurposeIsotropic high-resolution three-dimensional (3D) magnetic resonance neurography (MRN) is increasingly used to depict even small and highly oblique nerves of the lumbosacral plexus (LSP). The present study introduces a T2 mapping sequence (T2-prepared 3D turbo spin echo) that is B1-insensitive and enables quantitative assessment of LSP nerves.MethodsIn this study 15 healthy subjects (mean age 28.5 ± 3.8 years) underwent 3 T MRN of the LSP area three times. The T2 values were calculated offline on a voxel-by-voxel basis and measured at three segments (preganglionic, ganglionic, postganglionic) of three LSP nerves (S1, L5, L4) by two independent investigators (experienced and novice). Normative data for the different nerves were extracted and intraclass correlation coefficients (ICCs) were calculated to assess reproducibility and interobserver reliability of T2 measurements.ResultsThe T2 mapping showed excellent reproducibility with ICCs ranging between 0.99 (S1 preganglionic) and 0.89 (L5 postganglionic). Interobserver reliability was less robust with ICCs ranging between 0.78 (S1 preganglionic) and 0.44 (L5 postganglionic) for S1 and L5. A mean T2 value of 74.6 ± 4.7 ms was registered for preganglionic segments, 84.7 ± 4.1 ms for ganglionic and 65.4 ± 2.5 ms for postganglionic segments, respectively. There was a statistically significant variation of T2 values across the nerve (preganglionic vs ganglionic vs postganglionic) for S1, L5, and L4.ConclusionOur approach enables isotropic high-resolution and B1-insensitive T2 mapping of LSP nerves with excellent reproducibility. It might reflect a robust and clinically useful method for future diagnostics of LSP pathologies.
Highlights
Introduction mapping of lumbosacral plexus (LSP) nervesWe evaluate the feasibility of this approach for extraction of quantitative T2 values from preselected LSP nerves, and hypothesize a high reproducibility and reliability of our newly introduced method
It has been demonstrated recently that 3D turbo spin echo (TSE) or 3D fast spin echo (FSE) combined with improved motion sensitized driven equilibrium (iMSDE) preparation can achieve this high isotropic resolution and even resolve small nerve branches [2,3,4,5,6]; high-resolution 3D magnetic resonance neurography (MRN) of the LSP area can be significantly affected by B0 and B1 inhomogeneities that frequently occur in this region
The sequence used for T2 mapping of LSP nerves in this study is similar to a recently developed sequence that was successfully applied to T2 mapping of thigh muscles in healthy subjects [8]
Summary
In this study 15 healthy subjects (mean age 28.5 ± 3.8 years) underwent 3 T MRN of the LSP area three times. Conclusion Our approach enables isotropic high-resolution and B1-insensitive T2 mapping of LSP nerves with excellent reproducibility It might reflect a robust and clinically useful method for future diagnostics of LSP pathologies. Isotropic high-resolution three-dimensional (3D) MRN has been repeatedly used in recent years to depict even small and highly oblique nerves of the brachial plexus or lumbosacral plexus (LSP) by allowing reformatting in multiple planes. In this context, 3D turbo spin echo (TSE) or 3D fast spin echo (FSE) are most commonly used for achieving isotropic high-resolution T2-weighted nerve imaging in or near a plexus [2,3,4]. Fat-suppressed 3D TSE imaging has recently been combined with the improved motion sensitized driven equilibrium (iMSDE) preparation to suppress vessel signal and improve plexus nerve delineation [5,6,7]
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