Why cant they just scan his head!?!

So I will bring this subject up. Those of you that know me know that I have been pushing doctors over the last several years to do an MRI or CT scan of Joeys head to make sure that there is no organic cause to his issues. My fight for this has moved up several notches in the past two days because of some disturbing developments.
Joey has had a fine hand tremor ever since the seroquel incident and we have learned to manage it and I think Joey has learned to live with it. However on his last home visit Joey did not just have a fine hand tremor  his whole body was tremoring. I can only describe it as Parkinson like tremors. Now what truly worries me is the sudden increase in severity, just a few weeks time. I am aware that the medications can cause a variety of these types of side effects but I can not wrap my head around the seemingly sudden onset. He has had no change in medications or dosages, he has had no major weight loss or weight gain. I just can not figure it out. I am concerned that his liver function could be impaired and that could be causing his metabolism of these medications to be compromised.
My next worry is the sudden slowing of his cognitive functioning. I again am aware that the medications could attribute to this but it seems to be a overnight development. Joseph has great difficulty in getting a full coherent  thought out. It takes great time for him to develop a full thought process and when he manages to do so the thoughts are so disorganized its often difficult to follow his train of thoughts.
He has complained of headaches since the dawn of time. Anyone would think this would be reasonable to say lets scan his head and make sure there is no issue. So what if it comes back negative at least we would know. But what if maybe just maybe this entire time we have treated my son mentally ill and he just has a lesion or tumor? The frustrating part is the tunnel vision by every doctor I have encountered that simple blames everything on his mental illness or associated medications. Mentally ill people get medically sick too and all symptoms of mental illness can also have a medical reason. I saw everyday in my field people with far less compelling symptoms get ct scan after ct scan, I don't think its too much to ask for them to extend the same thought to my son.
Well that is my rant and rave for the day. Let the battle continue and hopefully one day someone will do it so I have a concrete evidence that there is nothing going on. In the meantime the doctors have ordered to check Joeys lithium and depakote levels again. I will keep you posted on the ongoing fight.