High resolution diffusion tensor imaging of human nerves in forearm

Abstract

Purpose To implement high resolution diffusion tensor imaging (DTI) for visualization and quantification of peripheral nerves in human forearm. Materials and Methods This HIPAA-compliant study was approved by our Institutional Review Board and written informed consent was obtained from all the study participants. Images were acquired with T1-and T2-weighted turbo spin echo with/without fat saturation, short tau inversion recovery (STIR). In addition, high spatial resolution (1.0 × 1.0 × 3.0 mm3) DTI sequence was optimized for clearly visualizing ulnar, superficial radial and median nerves in the forearm. Maps of the DTI derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ//) and radial diffusivity (λ⊥) were generated. Results For the first time the three peripheral nerves, ulnar, superficial radial and median, were visualized unequivocally on high resolution DTI-derived maps. DTI delineated the forearm nerves more clearly than other sequences. Significant differences in the DTI-derived measures, FA, MD, λ// and λ⊥, were observed among the three nerves. A strong correlation between the nerve size derived from FA map and T2-weighted images was observed. Conclusions High spatial resolution DTI is superior in identifying and quantifying the median, ulnar and superficial radial nerves in human forearm. Consistent visualization of small nerves and nerve branches is possible with high spatial resolution DTI. These normative data could potentially help in identifying pathology in diseased nerves.

Denoising of diffusion MRI improves peripheral nerve conspicuity and reproducibility

“…Overall, this study's findings support the hypothesis that combining the two denoising techniques effectively improves SNR and nerve conspicuity, overcoming challenges in accurately determining measures of nerve integrity from quantitative dMRI within a clinically feasible scan time. Importantly, the results support previous findings that SNR affects derived FA values and may at least partially explain previously reported variability in FA of nerves in healthy controls . Combining PCA and genSD denoising methods resulted in FA values similar to the benchmark (ie, "average" dataset), thereby improving the diagnostic accuracy of dMRI of peripheral nerves within the extremities.…”

Peripheral nerve diffusion tensor imaging: Overview, pitfalls, and future directions

“…Establishing normative DTI values is crucial to increase the confidence of detecting pathology, particularly in milder forms of peripheral neuropathy that may only result in small changes in DTI parameters. Multiple studies, however, have demonstrated a wide range in DTI values of upper extremity peripheral nerves in healthy cohorts . There is significant variation in trends of DTI metrics, with most studies showing a decrease in FA and increase in ADC in the median nerve when moving from proximal to distal in the forearm, an increase in FA with no difference in ADC, and a decrease in ADC with no change in FA in normal volunteers.…”

“…Ultimately, more studies are needed to confirm a trend. Moreover, there are inter‐nerve DTI differences between the ulnar, median, and radial nerves . Some of this variability may be explained by insufficient spatial resolution and SNR.…”

MRI biomarkers of proximal nerve injury in CIDP

“…This method is useful to provide anatomical data and to detect pathologies such as tumors that affect the continuity of nerves 18, 19. More recently, diffusion tensor imaging of peripheral nerves has been introduced as a tool to quantify nerve damage and regeneration 20, 21, 22…”