I don't know about the availability of perfusion MRI's at the Behcet's Centres of Excellence, but it might be helpful to print out the full color version of the article I gave a link to and discuss it with your neurologist. It's common for Behcet's patients to have "normal" MRI brain scans when evidence of the problem could be found with p-MRI's or SPECT scans.
Headaches in Behcet's can be severe, like vascular migraines, and can cause cognitive (thinking) and balance problems. I suffered from these for years and was treated with migraine medicines, high dose prednisone, Enbrel, Remicade, methotrexate, Cellcept, Imuran, you name it. Caffeine, either via coffee or caffeine pills, are also helpful to shrink swollen brain blood vessels. All these drugs would help somewhat, but the Behcet's migraines kept coming back.
My Behcet's headaches struck in the lower back of my head and even made it too painful to rest my head on a pillow. They had a sensation of warmth and the pain would spread up from the back to the top of my head all around, not limited to one side. Mine did not cause photophobia (sensitivity to light) or sensitivity to noise, but sometimes the pain was so bad I also vomited. My neurologist called them "atypical migraines" and agreed that they were caused by my Behcet's even though my MRI's were normal.
When I had these headaches I would become confused and had trouble thinking, talking, and typing on the computer. I could always tell the difference between these Behcet's headaches and my sinus headaches, tension headaches, occipital neuralgia, and exertional migraines. Fortunately after years of on-and-off Behcet's headaches, I get them very infrequently now. Before I developed these severe Behcet's headaches, I was still able to work, but after they began, I was approved for full disability benefits.
did your headaches last for weeks like severe pain and vomiting with out any let up and may I ask what medication helped you ? 
Thanks Amietamant.
Your headaches seem pretty much like mine and in the same place alougth lately I have been getting new one's in the frontal lobe area which are more accutely affecting speech, vision, memory, working familiar items [computer, setting up TV recordings , oven timer etc] and behaviour/personality....I also have ptosis down one side of my face and this also becomes very aggrovated at this time.
The MRI picked up lots of tiny live lesions in this area and so I would think the p-MRI's or SPECT scans would be useful and more indepth to locate the specific areas this is affecting.
The behaviour/personality problem is really quite distressing at times and at these times, I have to work hard to keep this on an even keel.
Do you happen to know where these scanners are available and is there easy access to them. I have heard of the SPECT scanners which I think are more widely available but haven't heard of where the p-MRI's are located. I live near London and so would think if thet were available it might be near here.
Andrea