A radiologist is a doctor who detects and treats conditions using medical imaging, like x-ray machines. If you think you've broken your arm after a fall at the roller rink, you may need to see a radiologist.
A radiologist can x-ray your arm or leg and get a picture of the bones inside. Other tools available to radiologists include CT scans, MRIs, and ultrasound. These are all imaging techniques, and the word radiologist comes from the radiation that x-rays and CT scans use to create an image (from the Latin radiationem, "a shining"). Instead of radiation, ultrasounds use sound waves and MRIs use magnetic fields and radio waves.