Axonal transport and MR imaging: prospects for contrast agent development

Axonal transport plays a critical role in the physiology and pathology of neurons, yet there have been virtually no clinical tools for its evaluation in human subjects. A wide variety of molecules that can act as axonal transport facilitators have been discovered and, in many cases, used to deliver labels detectable with histologic methods. Recently a number of investigators have reported preliminary success in developing intraneural contrast agents based on various versions of dextran-coated magnetite that may render magnetic resonance imaging capable of depicting axonal transport. It is not yet clear whether any clinically useful agents will eventually be developed, but there has been considerable progress in identifying design factors for such a pharmaceutical agent.