An MRI machine is a large, cylinder shaped machine that contains a very strong donut-shaped magnet. Magnets are commonly measured using gauss and an MRI magnet can be up to 20,000 gauss (common refrigerator magnets are around 10 gauss). However, even a magnet of 20,000 gauss is not harmful to humans (much stronger magnets have been tested with no ill effects). The patient lies on a bed that moves in and out of the machine during the process. The machine is connected to a computer that receives signals from the MRI unit. The computer interprets the signals and generates a 3-D image of the patient's body.(1) (2)
MRI, unlike x-rays and CT scans, does not use ionizing radiation. Instead, it uses radio waves that interact with specific molecules in the body (protons, the nuclei of hydrogen atoms).(3) During the exam, radio signals are repeatedly turned on and off. The energy in the radio waves is absorbed by different atoms in the target area and reflected back out of the body. When the radio waves are reflected off tissues in the patient's body, they generate signals that are detected by the MRI machine. These signals are sent to the MRI computer, which collects the signals from the coil and combines them to create a 3-D image.(4)
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