420 Words

Magnetic resonance imaging

Very Short Introduction

Magnetic resonance imaging (MRI)

is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of 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 CT and 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.

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.

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. 

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 MRI, 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 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

extends 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.

-- Wikipedia