Bma Illustrated Medical Dictionary

The patient lies inside a scanner sur-

rounded by a large, powerful magnet. A

receiving magnet is then placed around

the part of the body to be investigated.

If large areas, such as the abdomen, are

to be imaged, the receiving magnet is

fitted inside the scanner; for a smaller

area, such as a joint, a magnet may be

placed around the part to be scanned.

The scanner generates a strong mag-

netic field, which causes the atoms in

the body to line up parallel to each

other. Short pulses of radio waves from

a radiofrequency source briefly knock the

atoms out of alignment. As the atoms

realign they emit tiny signals, which are

detected by the receiving magnet. Infor-

mation about these signals is passed to

a computer, which builds up an image

based on the signals’ strength and loca-

tion. MRI images can be enhanced by

use of a contrast mediumto highlight

particular body structures, such as

tumours and blood vessels.

Images from MRI are similar to those

produced by CT scanning but give

greater contrast between normal and

abnormal tissues. MRI is useful in

studying the brain and spinal cord, the

internal structure of the eye and ear, the

internal organs, and blood flow.

There are no known risks or side effects.

The technique does not use ionizing

radiation and can be performed repeat-

edly, but the scanner may interfere with

the functioning of pacemakers, hearing

aids, and other electrical devices.

MRSAThe abbreviation for methicillin-

resistant STAPHYLOCOCCUS AUREUS, a

bacterium resistant to methicillin and

many other antibiotic drugs. MRSA is

responsible for the emergence of infec-

tions in hospitals that are difficult to

treat and can sometimes be fatal.

MSThe abbreviation for the disorder

multiple sclerosis.

MSGThe abbreviation for the food

additive monosodium glutamate.

MSUThe abbreviation for midstream

specimen of urine: a specimen of urine

to be examined for the presence of

microorganisms. The initial part of the

stream is not collected, in order to

avoid bacterial contamination of the

specimen from the skin or the lining of

the lower urinary tract.

mucoceleA swollen sac or cavity within

the body that is filled with mucus

secreted by its inner lining.

mucolytic drugsDrugs that make spu-

tum (phlegm) less sticky and easier to

cough up. An example is acetylcysteine.

MRSA MUCOLYTIC DRUGS

M

MRI

MRI scanner

Control

panel

Motorized

bed moves

patient into

scanner

Receiving magnet

picks up signals

produced by body in

response to radio waves

Powerful magnet

creates magnetic

field

Radiofrequency source

emits pulses of radio waves

Companion to

reassure patient