More cases of patients being overexposed to radiation during brain scans in US hospitals are being investigated, according to government officials.
It is thought medical devices by General Electric and Toshiba may have given patients up to eight times the recommended dose, the US Food and Drug Administration (FDA) said.
Patients overexposed to radiation during CT perfusion scans of the brain are facing the problems of cataract and cancer risks, said the US regulator.
The FDA also said that some patients had skin redness and hair loss.
The FDA has investigated 206 cases of overexposure to CT radiation at Cedars-Sinai Medical Center in Los Angeles during an 18-month period.
It has identified at least 50 more cases at Cedars-Sinai and two other California hospitals.
The FDA has advised imaging centres to check the right amount of radiation is being delivered before the use of CT perfusion scans.