headaches

Hi Ladies:
I haven't posted in awhile, but here I am with a woe. I have had a headache for about 2 weeks, and it especially hurts if I laugh or cough. I had a bad headache last night when I went to bed and a bad headache when I woke up this morning. I talked to the nurse at my oncologist's, and she said she would talk to the dr. about a CT scan of my head. My question is--how does a CT scan compare with an MRI? I think I've read here before about people's preferences for one over the other. I have had neither.
A brief history--I had mets to liver and bones dx'd aug 2002. I received a vaccine for her2++ metastatic b/c in Aug/Sept 2003. The dr. told me in Nov that I'm in remission (yeah!), but the vaccine is like chemo--it doesn't cross the blood/brain barrier, so of course I am always concerned about my brain.
I'm very interested in your opinions about headaches and diagnostic tests.
Thanks so much.
Carla