I hear you that sometimes it can be difficult to open up about hard things that have happened in your past. But I like to remember that secrets keep us sick. In order to heal, we must share what has been hurting us. Therapists are a safe person to share the hurt with, even though it's uncomfortable to talk about how an event was traumatic. I'm sorry it happened to you. If you feel uncomfortable sharing, maybe you might consider looking for a specific trauma based counselor, like one specialized in EMDR.

PTSD does change the way the brain functions, especially in a more profound way for younger people. It especially changes the way the midbrain and hippocampus process memory. Most of the time, a PTSD diagnosis isn't going to need a PET scan. It's a symptom based diagnosis. However, a professional can make the final call as to whether or not that would be helpful for your case.

Hope this helps.