<unk>  <unk>  is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body.<unk>  scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body.<unk>  does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans.<unk>  is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy.<unk>  is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. Compared to CT,<unk>  provides better contrast in images of soft-tissues, e.g. in the brain or abdomen. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube. Additionally, implants and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an<unk>  examination safely.<unk>  was originally called NMRI (nuclear<unk> , but "nuclear" was dropped to avoid negative associations. Certain atomic nuclei are able to absorb radio frequency energy when placed in an external magnetic field; the resultant evolving spin polarization can induce a RF signal in a radio frequency coil and thereby be detected. In clinical and research<unk> , hydrogen atoms are most often used to generate a macroscopic polarization that is detected by antennae close to the subject being examined. Hydrogen atoms are naturally abundant in humans and other biological organisms, particularly in water and fat. For this reason, most<unk>  scans essentially map the location of water and fat in the body. Pulses of radio waves excite the nuclear spin energy transition, and magnetic field gradients localize the polarization in space. By varying the parameters of the pulse sequence, different contrasts may be generated between tissues based on the relaxation properties of the hydrogen atoms therein. Since its development in the 1970s and 1980s,<unk>  has proven to be a versatile imaging technique. While<unk>  is most prominently used in diagnostic medicine and biomedical research, it also may be used to form images of non-living objects, such as mummies. Diffusion<unk>  and functional<unk>  extend the utility of<unk>  to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. The sustained increase in demand for<unk>  within health systems has led to concerns about cost effectiveness and overdiagnosis.
Magnetic resonance imaging
Magnetic field imaging
Magnetic Resonance in Medicine
Electron resonance imaging
Radiography
Autoradiograph
Functional imaging
Myelography