At a time when Americans receive far more diagnostic radiation than ever before, two cases under scrutiny in California  one involving a large, well-known Los Angeles hospital, the other a tiny hospital in the northern part of the state  underscore the risks that powerful CT scans pose when used incorrectly.

A week ago, Cedars-Sinai Medical Center in Los Angeles disclosed that it had mistakenly administered up to eight times the normal radiation dose to 206 possible stroke victims over an 18-month period during a procedure intended to get clearer images of the brain. State and federal health officials are investigating the cause.

Hundreds of miles north at Mad River Community Hospital in Arcata, the other case  involving a 2 ½-year-old boy complaining of neck pain after falling off his bed  has led to the revocation of an X-ray technician’s state license for subjecting the child to more than an hour of CT scans. The procedure normally takes two or three minutes.

The hospital’s radiology manager at the time, Bruce Fleck, called the overdose a “rogue act of insanity.” Robert Schlag, chief of the state’s division of Food, Drug and Radiation Safety, said it was “one of the more egregious, extreme cases that I have ever seen.”