Magnetic resonance neurography.

We have made cross-sectional image "neurograms" in which peripheral nerve has a greater signal intensity than that of other tissue. Neurographic images of the rabbit forelimb were obtained using a spin-echo magnetic resonance imaging (MRI) technique that combines fat suppression and diffusion weighting. After fat suppression the nerve shows up in relative isolation and is brighter than the surrounding tissue due to its longer T2 relaxation time of approximately 50 ms compared to approximately 27 ms for muscle. The addition of pulsed gradients for diffusion weighting of the MR signal further enhances the intensity of the nerve signal relative to that of surrounding muscle tissue. The greater diffusional anisotropy of nerve tissue (D parallel/D perpendicular = 3.1) compared to that of muscle (D parallel/D perpendicular = 1.9) allows further enhancement of the nerve by a subtraction of two diffusion-weighted images, one with the gradients oriented parallel and one with the gradients oriented perpendicular to the nerve orientation. We show that by manipulation of the MRI parameters, either echo time or pulsed gradient strength, the nerves can be made to show up as the most intense feature. This verifies the feasibility of generating three-dimensional "neurographic" images, analogous to angiograms, but which demonstrate the peripheral nerve tracts in apparent isolation.