If I had these types of questions, I would talk to the practitioner that ordered the studies, or talk to my current doc.
Often the answer to one question will provoke another question, so sitting down to talk with the doc is probably the best way to go.
bob
Or maybe a google search on the terms you are looking for would turn up information like this:
Dorsal means back, ventral means front. As the body is symmetrical, the same thing happens on both the left and right side of the body. This happens in each vertebra of the spine.
http://en.wikipedia.org/wiki/Spinal_nerve
Good luck
bob