Father refuses to be tested for Dementia.

My father's doctor suspects that he has dementia. The doctor wants to do a CT scan which my dad refuses. Not only does my dad show memory loss his behavior can be frightening. The most recent episode he becomes angry and starts yelling awful things to my mother. Example: "Your just waiting for me to die." When my mom called an ambulance for help he started yelling that he was going to kill her. My father is also diabetic and she thought at first that maybe it had to do with his diabetes. This behavior from my dad is totally uncharacteristic of him. Both my parents need help and support. I am trying to find resources for my mom so she doesn't feel so helpless and alone.