Stroke victims are having to wait more than 24 hours for a brain scan because of "unacceptable variations" in the way hospitals operate, MPs have said.
Only half of patients receive treatment vital to prevent permanent brain damage because scanners are not being fully used.
Opening hours vary from 40 to 100 hours a week between hospitals and there is an almost threefold difference in the number of scans carried out per machine. Also, hospital trusts are not co-operating to buy scanners jointly to drive down the price.
Margaret Hodge, chairwoman of the Commons Public Accounts Committee, said: "The way this equipment is bought and used is not providing value for money for the taxpayer. We were shocked by the unacceptable response times for certain conditions."
Simon Burns, Health minister, said: "The Government is determined to root out waste. Already the NHS has saved up to 15 per cent on scanners by working with NHS Supply Chain to co-ordinate large orders over time with other trusts."