The assault occurred Wednesday in the radiology unit.
Investigators say 25-year-old Terance Tekoh was a contracted certified nursing attendant for Cross County Per Diem. The company provides contract medical personnel to the hospital.
"The suspect, in this case, was responsible for transporting the victim from a room or waiting area by gurney to the room where the procedure was to take place," said Los Angeles Co. Sheriff's Department Lt. Steven Katz. "At some point, while the suspect was alone with the victim in this examination room, the sexual assault occurred."
He was arrested at the medical center Wednesday evening after the victim reported the incident to authorities.
"It's a sad state of affairs. In that environment, you're exceptionally vulnerable, and as a result it makes it that much more of a difficult situation for anyone to have to contend with," said Katz.
Tekoh worked at the hospital since July 27, 2012, and was assigned to the Magnetic Resonance Imaging Department. His employment has since been terminated, according to the sheriff's department.
He was booked at the sheriff's East Los Angeles Station on charges of sexual penetration by a foreign object. He is now free after posting $100,000 bail.
Tekoh is expected to appear in Los Angeles Superior Court on April 10.
Investigators were seeking the public's help in identifying any other potential victims. Anyone with information was urged to contact Lt. Steve Katz of the sheriff's Special Victims Bureau at (562) 946-7901.
CNS contributed to this report.