Nerve Imaging: Discoveries and Science

Major Discoveries and Basic Science

Initial discovery of Neurography described in a technical paper on the scientific basis of Neurography. 1) Chemical shift suppression reduced signal from isotropic water in nerve resulting in a six fold increase in apparent coefficient of diffusion anisotropy in nerve - the basis for diffusion Neurography. 2) The T2 of nerve has been grossly miscalculated in the past - old measures averaged the T2 of fascicle and inter-fascicle water (T2 relaxation shorter than muscle), but the true T2 is much longer (T2 relaxation rate longer than muscle) laying the basis for T2-Neurography. Animal studies at 4.7 Tesla with 100 mT/m gradients.

The first clinical human projection nerve image. T2 Neurography used with phased-array coils allows for good visualization of nerve fascicles. Dramatic improvement over existing approaches to nerve imaging can be accomplished in a production model clinical MR scanner.

Muscle hyperintensity begins as soon as four days after loss of the innervating nerve. A single image sequence can demonstrate both nerve and muscle abnormalities.

First major overview of utility of Neurography reporting on 202 clinical imaging studies and 52 normals. Covered fifteen different body regions and six different categories of pathology. Several key capabilities of Neurography demonstrated: 1) Normal nerves can be imaged reliably in many body locations, 2) capability of distinguishing intra-neural from peri-neural tumors, 3) nerve identification is improved by capability of generating longitudinal nerve images and by showing fascicle structure, 4) nerve continuity can be checked at the fascicular level after trauma, 5) focal increases in nerve diameter and intensity occur in some types of nerve pathology and the time course of the image findings reflects progression of or recovery from the pathology, 6) focal identification of nerve compression makes smaller surgical incisions possible in many cases.

Nerve fascicle hyperintensity correlates with decreased conduction measured intra-operatively. Also, the physical appearance of nerves and their relationships to tumors depicted in projection nerve imaging correlates precisely with the appearance of these structures as seen during operation. Detailed preoperative information on the relation of fascicle groups to tumors improved the potential for good outcome by providing better information than could be obtained under direct vision. It also helped in deciding on the operability of some lesions.

Nerve hyperintensity associated with Wallerian degeneration resolves as a nerve recovers function after graft repair.

Nerve imaging can be applied to make very specific diagnoses concerning injuries in the brachial plexus. The images can be used to improve understanding of the radiological anatomy as well as to improve the accuracy of diagnoses.

In a rat model, quantitative measurements confirm that there is significant hyperintensity at the site of compression and to an even greater degree distal to the site of compression.

Nerve hyperintensity became maximal after 14 days in rats with a compressive nerve injury. The hyperintensity resolved as the nerve function recovered.