The NHS increased its reliance on the private sector yesterday by signing a deal to buy radiography scans for more than 600,000 patients during the next five years.

Alliance Medical, a British supplier of diagnostic equipment, will do the work in 12 mobile units that will visit English hospitals .

The contract, understood to be worth about £90m, will increase the NHS's capacity by 15%. Ministers believe it will help it to meet new targets for reducing waiting times. They are planning to negotiate further private-sector deals .

The mobile units will carry out the magnetic resonance imaging (MRI) scans that are used to diagnose cancers and conditions as diverse as migraine, epilepsy, and heart dis ease. The deal is a coup for Alliance Medical, which operates 45 mobile units in Britain, Italy and Spain.

The new units will begin work toward the end of next month and should complete up to 110,900 extra scans in the first year.