3-DIMENSIONAL ANISOTROPY CONTRAST MAGNETIC-RESONANCE-IMAGING OF THE RAT NERVOUS-SYSTEM - MR AXONOGRAPHY

Anisotropy of apparent diffusivities (D-app) of water molecules is known to be an excellent means for elucidating detailed information regarding neuronal fiber direction and density in live subjects (axonography). Nevertheless, determination of eigenvalues and eigenvectors of the apparent diffusion tenser, D-app(xi), the necessary process for the treatment of D-app(xi) in axonography, is cumbersome and the quality of the reconstructed images based on estimated parameter values of D-app(xi) has often been disappointing. We present here a simple algorithm which allows for the extraction of the anisotropic term vector, D-app(A) form, which in turn provides a novel color-coded contrast for magnetic resonance imaging (MRI). MRI images constructed using this technique, three-dimensional anisotropy contrast (3DAC), provided impressive anatomic resolution of the CNS, comparable to in vitro histology. Directional information of D-app(A) expressed by hue of color clearly correlated to fiber direction, while magnitude of D-app(A) expressed by intensity of color correlated to fiber diameter. Magnetic resonance axonography (MRX) utilizing 3DAC technique possesses significant potential for various biological and clinical applications.