Diffusion Tensor Sequences (DTI) for Study of Lumbar Roots by Magnetic Resonance Imaging (MRI)

For every healthy volunteer will be acquired: * a morphological sequence * a reference diffusion tensor sequence covering three lumbar stages (reference DTI), * a diffusion tensor sequence acquired in multiband technique, covering three lumbar stages (optimized DTI), * a diffusion tensor sequence acquired in a multiband technique, covering a lumbar stage, of higher spatial resolution (centred DTI)