The U.S. government health insurance plan for the elderly and disabled will pay for doctors to run PET brain scans to diagnose Alzheimer’s disease, U.S. officials said on Thursday.

Medicare will cover the positron emission tomography scans for those patients who show signs of both Alzheimer’s and dementia but whose final diagnosis “remains uncertain,” as well as other patients who enroll in a government-run trial, officials said.

“We ought to approve coverage for patients who’ve been worked up but whose diagnosis is uncertain,” said Mark McClellan, head of the agency that oversees Medicare and Medicaid.

Doctors have said the scans could help them diagnose Alzheimer’s earlier, giving patients time to perhaps start medication and make arrangements. They may also help show how well the drugs are working, doctors said.

A scan can cost $1,200, and each machine costs a hospital or clinic about $2 million to install.

At least 4.5 million Americans have Alzheimer’s and that number is expected to rise to as high as 16 million by 2050 as the population ages.