New cases of radiation overdose has heightened the FDA’s ongoing investigation into perfusion-related radiation in hospitals.

Bakersfield Memorial Hospital said 16 potential stroke patients were exposed to higher-than-recommended levels of radiation and more overdoses were discovered at least four Los Angeles County hospitals - Cedars-Sinai Medical Center, Los Angeles County-USC Medical Center, Glendale Adventist Medical Center and Providence St. Joseph Medical Center.

Last year in December, the FDA opened an investigation in response to reports that several hospitals around the country had overexposed patients.

At least 400 patients from eight hospitals have experienced higher-than-recommended levels of radiation from CT brain perfusion scans, according to a report by the Times.

Health officials estimate the number of patients affected by high radiation levels is far greater and includes additional facilities in other states.

Doctors can sometimes misdiagnose patients showing symptoms of radiation overexposure, thinking that they are caused by a stroke rather than the radiation, said a lawyer representing more than 100 patients allegedly experienced brain perfusion radiation overdose.

Memorial reported that 16 patients undergoing Computed Tomography brain perfusion received radiation up to five and a half times the recommended level despite following guidelines provided by its Toshiba medical-imaging devices.

The FDA is unsure of the causes of the overdose. "Is this an error associated with the machine? A design error? A user error? And primarily, is it an error at all?" said Dick Thompson, a spokesman for the agency. “Until our investigation is final and released, we have to have an open mind.”

The FDA is to release a final report on the investigation within the coming months.