good old You tube -
http://www.youtube.com/watch?v=k0uSpYd_Ics
I think the equipment used for mine was a little bit different that in this video , but the general info is the same.
*I suggest not having a full bladder
just in case they happen to hit a very sensitive area. But it only zap/zings for a second or less.
Only my arms were tested so I didn't have to disrobe fully -maybe just had a paper top cover.
But don't expect it to really prove TOS , mostly it will show if one of the nerves is actually being affected or not, which could possibly be something called double crush or even triple crush if TOS + ulnar or carpal or TOS + carpal + ulnar.
If it all comes up as normal, TOS can still be suspected as it can involve the smaller sensory nerves that are much harder to test.
I hope the PT is very good & an expert.
We also have some threads with self care ideas that might help.
If you can list some of your most bothersome symptoms maybe we can suggest some specific things for you to try.