Diffusion Tensor Imaging of Lumbar Nerve Roots: Comparison Between Fast Readout-Segmented and Selective-Excitation Acquisitions.

OBJECTIVES: The aim of this study was to compare the quality of recently emerged advanced diffusion tensor imaging (DTI) techniques with conventional single-shot echo-planar imaging (EPI) in a functional assessment of lumbar nerve roots.
MATERIALS AND METHODS: The institutional review board approved the study including 12 healthy volunteers. Diffusion tensor imaging was performed at 3 T (MAGNETOM Skyra; Siemens Healthcare) with b-values of 0 and 700 s/mm and an isotropic spatial resolution for subsequent multiplanar reformatting. The nerve roots L2 to S1 were imaged in coronal orientation with readout-segmented EPI (rs-DTI) and selective-excitation EPI (sTX-DTI) with an acquisition time of 5 minutes each, and in axial orientation with single-shot EPI (ss-DTI) with an acquisition time of 12 minutes (scan parameters as in recent literature). Two independent readers qualitatively and quantitatively assessed image quality.
RESULTS: The interobserver reliability ranged from "substantial" to "almost perfect" for all examined parameter and all 3 sequences (κ = 0.70-0.94). Overall image quality was rated higher, and artifact levels were scored lower for rs-DTI and sTX-DTI than for ss-DTI (P = 0.007-0.027), while fractional anisotropy and signal-to-noise ratio values were similar for all sequences (P ≥ 0.306 and P ≥ 0.100, respectively). Contrast-to-noise ratios were significantly higher for rs-DTI and ss-DTI than for sTX-DTI (P = 0.004-0.013).
CONCLUSIONS: Despite shorter acquisition times, rs-DTI and sTX-DTI produced images of higher quality with smaller geometrical distortions than the current standard of reference, ss-DTI. Thus, DTI acquisitions in the coronal plane, requiring fewer slices for full coverage of exiting nerve roots, may allow for functional neurography in scan times suitable for routine clinical practice.