Everyone provided really good information. I just wanted to add the following link which has great information about CAT scans from University of Wisconsin Hhspitals and Clinics Authority.
Take care and keep us posted!
A CAT scan (Computerized Axial Tomography), also known as a CT scan, uses x-ray technology to produce cross-sectional images of the internal body, including brain structure and size, which may be helpful in the diagnosis of conditions such as Alzheimer's disease. The procedure is very quick; depending upon the part of the body being scanned, the test itself will take about 10-15 minutes.
A CAT scan takes between 10 and 30 minutes.
Taking a ct scan once in a while is fine. However, if the person with dementia has trouble to stay still, someone like family member may need to be there with the person when he/she takes the scan.
Ct scan has radiation but if you just take it once for all for diagnosis, it is worth doing.