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Magnetic resonance imaging (MRI), or
nuclear magnetic resonance imaging (NMRI), is
primarily a
medical imaging
technique most commonly used in
radiology to visualize detailed internal structure and
limited function of the body. MRI provides much greater
contrast between the different soft tissues of the body
than
computed tomography (CT) does, making it especially
useful in
neurological (brain),
musculoskeletal,
cardiovascular, and
oncological (cancer) imaging. Unlike CT, it uses no
ionizing
radiation, but uses a powerful
magnetic field to align the
nuclear magnetization of (usually)
hydrogen
atoms in water in the body.
Radio frequency
(RF) fields are used to systematically alter the alignment
of this magnetization, causing the hydrogen nuclei to
produce a rotating magnetic field detectable by the scanner.
This signal can be manipulated by additional magnetic fields
to build up enough information to construct an image of the
body.
Magnetic resonance imaging is a relatively new
technology. The first MR image was published in 1973
and the first cross-sectional image of a living mouse was
published in January 1974.
The first studies performed on humans were published in
1977.
By comparison, the first human
X-ray image was taken in 1895.
Magnetic resonance imaging was developed from knowledge
gained in the study of
nuclear magnetic resonance. In its early years the
technique was referred to as nuclear magnetic resonance
imaging (NMRI). However, because the word nuclear was
associated in the public mind with
ionizing
radiation exposure it is generally now referred to
simply as MRI. Scientists still use the term NMRI when
discussing non-medical devices operating on the same
principles. The term magnetic resonance tomography (MRT) is
also sometimes used.
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