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

To define the optimal acquisition parameters for diffusion tensor imaging of the median nerve at the wrist and to measure the diffusion values.

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.

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.

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.