Scanners are electronic devices that move backwards and forwards in lines in order to build up a picture.
Image scanners are used to convert pictures and other material into a digital form for computers to read.
A photoelectric cell in the scanner measures the amount of light reflected from each part of the picture and converts it into a digital code.
Various scanners are used in medicine to build up pictures of the inside of the body. They include CT scanners, PET scanners and MRI scanners.
CT stands for computerized tomography. An X-ray beam rotates around the patient and is picked up by detectors on the far side to build up a 3-I) picture.
PET stands for Positron Emission Tomography. The scanner picks up positrons (positively charged electrons sent out by radioactive substances injected into the blood.
PET scans can show a living brain in action.
MRI stands for Magnetic Resonance Imaging.
An MRI scan works like CT scans but it uses magnetism, not X-rays. The patient is surrounded by such powerful magnets that all the body’s protons line up.
The MRI scan begins as a radio pulse that knocks the protons briefly out of alignment. The scanner detects radio signals sent out by the protons as they snap back into line. This PET scan shows a monkey’s brain from above displays on a monitor.