3T tractography of the median nerve: optimisation of acquisition parameters and normative diffusion values.

Purpose: To define the optimal acquisition parameters for diffusion tensor imaging of the median nerve at the wrist and to measure the diffusion values.
Patients and Methods: The wrists of 14 healthy volunteers were explored using 3T MRI with a dedicated wrist coil. Each examination consisted of six sequences, varying the number of directions (15-20-30) and the b values (500-800-1000-2000s/mm(2)). The tractography images were evaluated by two radiologists using a qualitative scale with six levels. The diffusion and anisotropy coefficients (ADC and FA) were measured and the values compared with the data in the literature.
Results: Median nerve tractography was successfully achieved in all sequences. The 20 direction sequence with b=1000s/mm(2) seemed to provide the best results for a reasonable acquisition time (5'38″). The diffusion values showed large interindividual variations.
Conclusion: Optimisation of acquisitions parameters is important in peripheral nerve tractography, and may facilitate a routine use of the technique. The images obtained are easy to analyse but the diffusivity and anisotropy coefficients are too variable, however, to be used in practice.
(Copyright © 2012 Éditions françaises de radiologie. Published by Elsevier Masson SAS. All rights reserved.)