From the article:
“Cognitive impairment, and accumulation in the brain of the abnormal proteins amyloid and tau, are what we currently rely upon to diagnose Alzheimer’s disease, but blood-brain barrier breakdown and cerebral blood flow changes can be seen much earlier,” said Berislav Zlokovic, the Mary Hayley and Selim Zilkha Chair in Alzheimer’s Disease Research at the Keck School of Medicine of USC. “This shows why healthy blood vessels are so important for normal brain functioning.”
[…]
BBB leaks can be detected with an intravenously administered contrast substance in concert with magnetic resonance imaging. Brain microbleeds, another sign of leakage, also can be picked up with MRI. A slowdown in the brain’s uptake of glucose, visible via PET scan, can be a another result of BBB breakdown. Zlokovic notes that these aren’t tests routinely offered at a doctor’s office.