In a procedure called diffusor tensor imaging (dti), the way in which diffuse(s) along the length of a nerve fiber is measured to determine how different nerves communicate with each other.

In a procedure called diffusor tensor imaging, the way in which water diffuses along the length of a nerve fiber is measure to determine how different nerves communicate with each other. 
DTI is a technique that detects how water travels along the white matter tracts in the brain. White matter is the area of the central nervous system that is mainly made up of myelinated axons, also called tracts. The DTI detects the white matter fibers that connect different parts of the brain. White matter tracts connect different parts of the brain and must be protected during surgery.

Ithink that b is correct but just in case wait to see if someone else answers