Global InformationMagnetic resonance imaging information
| Magnetic resonance imaging | |
|---|---|
Para-sagittal MRI of the head, with aliasing artifacts (nose and forehead appear at the back of the head) | |
| Synonyms | Nuclear magnetic resonance imaging (NMRI), magnetic resonance tomography (MRT) |
| ICD-9-CM | 88.91 |
| MeSH | D008279 |
| MedlinePlus | 003335 |
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from computed tomography (CT) and positron emission tomography (PET) scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy.[1]
MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. Compared to CT, MRI 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, although "open" MRI designs mostly relieve this. Additionally, implants and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an MRI examination safely.
MRI was originally called NMRI (nuclear magnetic resonance imaging), but "nuclear" was dropped to avoid negative associations.[2] Certain atomic nuclei are able to absorb radio frequency (RF) 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.[3] In clinical and research MRI, hydrogen atoms are most often used to generate a macroscopic polarization that is detected by antennas close to the subject being examined.[3] Hydrogen atoms are naturally abundant in humans and other biological organisms, particularly in water and fat. For this reason, most MRI 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, MRI has proven to be a versatile imaging technique. While MRI 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 MRI and functional MRI extend the utility of MRI to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. The sustained increase in demand for MRI within health systems has led to concerns about cost effectiveness and overdiagnosis.[4][5][dubious ]
- ^ Rinck, Peter A. (2024). Magnetic Resonance in Medicine. A critical introduction. e-Textbook (14th ed.). TRTF – The Round Table Foundation: TwinTree Media. "Magnetic Resonance in Medicine". www.magnetic-resonance.org.
- ^ McRobbie DW, Moore EA, Graves MJ, Prince MR (2007). MRI from Picture to Proton. Cambridge University Press. p. 1. ISBN 978-1-139-45719-4.
- ^ a b Hoult DI, Bahkar B (1998). "NMR Signal Reception: Virtual Photons and Coherent Spontaneous Emission". Concepts in Magnetic Resonance. 9 (5): 277–297. doi:10.1002/(SICI)1099-0534(1997)9:5<277::AID-CMR1>3.0.CO;2-W.
- ^ [irrelevant citation]Smith-Bindman R, Miglioretti DL, Johnson E, Lee C, Feigelson HS, Flynn M, et al. (June 2012). "Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996-2010". JAMA. 307 (22): 2400–9. doi:10.1001/jama.2012.5960. PMC 3859870. PMID 22692172.
- ^ Health at a glance 2009 OECD indicators. 2009. doi:10.1787/health_glance-2009-en. ISBN 978-92-64-07555-9.