Still, he said he encountered a medical culture resistant to sharing data, owing to tradition, business practices and legal concerns.

“The person with the least access to data in the system is the patient,” he said. “You can get it, but the burden is always on the patient. And it is scattered across many different silos of patient data.”

Since his diagnosis last summer, Mr. Keating has become a passionate advocate for giving patients all the medical data they ask for. He has given talks at M.I.T., where he studies mechanical engineering, he has met with doctors, hospital administrators and researchers, and he has been invited to the White House.

He knows that what he is pushing goes against convention.

To a hospital, a patient is a revenue-generating asset, said Ben Shneiderman, a professor at the University of Maryland who is a health technology expert. Hold onto the patient’s information, and you are more likely to keep the patient. Health software suppliers have traditionally sold closed, proprietary systems, which tend to lock in customers.

“The problem is that you have institutions whose business models do not favor sharing information, either with other hospitals or patients,” said Mr. Shneiderman.

Yet the economic incentives for data-sharing, some medical experts say, are beginning to fall into place. Increasingly, providers will be paid a set amount of money for a population of patients, an approach called accountable care, and a departure from fee-for-service reimbursement in which doctors and hospitals are paid for each test and treatment.