Federal health regulators have identified 50 more patients exposed to dangerous radiation levels from brain scans at a hospital in Los Angeles.

The Food and Drug Administration says more than 250 patients at Cedars-Sinai Medical Center have received dangerous CT scans in the last 18 months. The brain scans are used to diagnose strokes.

The agency reported in October that more than 200 patients at the hospital had been put at risk. FDA officials say it's unclear whether the problems are being caused by human error or a problem with CT equipment.

Cedars-Sinai uses a scanner from General Electric. But FDA officials have reported problems at other hospitals using different brands of scanners, including models from Toshiba.