How to get a brain scan or other tests in the "preclinical

Hi,
My husband is 38. He is demonstrating slight memory and judgment lapses complicated by a hearing loss. His father and paternal grandfather both had Alzheimers disease (father was early-onset)

I am very concerned. I've read that if you can diagnose something in the preclinical years (before bad symptoms develop) you have a better shot of reversing or preventing some of the damage. But I don't know where I can get my husband a functional MRI scan or other diagnostic tests.

He is assured because his father is the only member of his extended family to have early onset form, but I am not reassured as one aunt died and we dont have information going back past 2 generations.

Thanks