Magnetic resonance imaging (MRI) uses magnetic fields to provide images of body tissues, helping diagnosis of certain conditions in adults and in children. MRI can be used to look at all parts of the body, including the brain, the heart, blood vessels, the spinal cord, and the extremities. Unlike x-ray tests, computed tomography (CT scans), and angiography, MRI does not use ionizing radiation. However, MRIs are noninvasive tests, like x-rays and ultrasound. Having an MRI does not hurt, although it is essential for the patient to lie completely still during the examination. This may be difficult for individuals who have anxiety, pain, or claustrophobia (fear of enclosed spaces). Sedation may be available for those persons and for children who require an MRI. Because the equipment used in an MRI produces loud noises, earplugs may be used if the MRI does not include examination of the head. Open MRI machines have less sense of confinement and may be preferred by persons who have concerns about being in a small enclosed space. Extremely obese persons may not fit into traditional MRI scanners, but open MRI machines can accommodate larger individuals. Performance of MRIs, like CT scans and other imaging studies, is usually supervised by a radiologist (a physician with specialized training in medical imaging and interpretation of those images).