High Isotropic Resolution T2 Mapping of the Lumbosacral Plexus with T2-Prepared 3D Turbo Spin Echo

Abstract

Purpose Isotropic 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. Methods In 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. Results The 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. 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.

T2 mapping of lumbosacral nerves in patients suffering from unilateral radicular pain due to degenerative disc disease

“…The scanning protocol included the following sequences: a flow-suppressed T2-weighted, 3D turbo spin echo (TSE) sequence with an isotropic voxel size of 2 mm to depict LSP anatomy, with the field of view (FOV) covering at least the LSP nerves L2-S2; 4,37 and an adiabatic T2-prepared, 3D TSE sequence with fat suppression using spectral attenuated inversion recovery and variable duration of the T2 preparation for the purpose of T2 mapping of LSP nerves with the following sequence parameters: FOV 38 × 38 × 8 cm 3 ; acquisition voxel 2 × 2 × 2 mm 3 ; echo train length 80; T2 preparation durations of 20/40/60/80 msec; TR 1.6 seconds; and TE of the TSE shot 15 msec. 25,37 A modified B1-insensitive rotation pulse was applied for T2 preparation in order to minimize the sensitivity to B0 and B1 inhomogeneities. 25,37 The same scanning protocol using the same MRI scanner has been applied previously in healthy subjects.…”

“…Recent studies have successfully applied T2 mapping of the LSP in healthy subjects, with the aim of providing normative T2 values and evaluating reliability. 29,37 However, research on quantitative MRN by means of T2 mapping is lacking in patients with LRS, although it might improve imagingbased diagnostics by providing more objective information about the affected nerves themselves instead of primarily enabling qualitative evaluation of compressing surrounding structures, as conventional anatomical MRI does.…”

Patient respiratory‐triggered quantitative T2 mapping in the pancreas

“…T 2 mapping has been introduced into clinical practice for various organs and tissues, including brain, [6][7][8] heart, 4,9 and cartilage. 5,[10][11][12] In neuroradiology, a microstructural change, such as neuronal loss or demyelination, results in increased free water and thus longer T 2 relaxation times and greater signal intensity on T 2 -weighted MRI images.…”

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

“…After exporting the data from the MRI scanner, T2 values derived from the 3D T2-prepared TSE sequence (in all healthy volunteers and all patients) and from the 2D MESE sequence (in six healthy volunteers) were calculated offline on a voxel-by-voxel basis with a combination of variable projection and golden section search assuming a mono-exponential signal decay [38][39][40][41]. A mono-exponential signal decay of the reported multi-compartment T2 decay of nerve tissue was employed because of the inherently strong T2 weighting of the proposed 3D T2-prepared TSE sequence.…”

“…The resulting T2 maps (one T2 map for the left and right side per healthy subject or patient and sequence) were successively opened in Horos (version 1.1.7; https ://www.horos proje ct.org) and color-coded according to a standardized scheme (Figs. 1,2) [40,41]. First, the distal sciatic nerve was carefully identified on axial slices of the color-coded T2 maps, co-registered to uncolored anatomical images of the 2D T2-weighted DIXON TSE sequence that served as reference for enhanced structural interpretability.…”