Bma Illustrated Medical Dictionary

produce high-quality images with the

lowest possible radiation exposure to the

patient. The possibility of genetic dam-

age can be minimized by using a lead

shield to protect the patient’s reproduc-

tive organs from X-rays. Radiographers

and radiologists wear a film badgeto

monitor their exposure to radiation.

(See also imaging techniques; radiogra-

phy; radiology.)

X-rays, dentalSee dental X-rays.

xylitol A naturally occurring carbohydrate

that is only partially absorbed by the

body and is sometimes used as a sweet-

ener by people with diabetes. Xylitol

chewing gum has been shown to reduce

recurrent ear infections in some children.

Excess xylitol may lead to abdominal

discomfort and flatulence.

xylometazolineA decongestant drug

used in the form of a spray or drops to

relieve nasal congestion caused by a

common cold, sinusitis, or hay fever (see

rhinitis, allergic). Xylometazoline is also

used as an ingredient of eye-drops in the

treatment of allergic conjunctivitis.

Excessive use of xylometazoline may

cause headache, palpitations, or drowsi-

ness. Long-term use of the drug may

cause nasal congestion to worsen when

treatment is stopped.

X-rays well and appear white on an X-

ray image. Soft tissues, such as muscle,

absorb less and appear grey.

Because X-rays can damage living

cells, especially those that are dividing

rapidly, high doses of radiation are used

for treating cancer (see radiotherapy).

Hollow or fluid-filled parts of the body

often do not show up well on X-ray film

unless they first have a contrast med-

ium (a substance that is opaque to

X-rays) introduced into them. Contrast-

medium X-ray techniques are used to

image the gallbladder (see cholecystogra-

phy), bile ducts (see cholangiography),

the urinary tract (see urography), the

gastrointestinal tract (see barium X-ray

examinations), blood vessels (see angiog-

raphy; venography), and the spinal cord

(see myelography).

X-rays can be used to obtain an image

of a “slice” through an organ or part of

the body by using a technique known as

tomography. More detailed images of a

body slice are produced by combining

tomography with the capabilities of a

computer (see CT scanning).

Large doses of X-rays can be extremely

hazardous, and even small doses carry

some risk (see radiation hazards). Modern

X-ray film, equipment, and techniques

X-RAY

X-RAYS, DENTAL XYLOMETAZOLINE

X

X-ray
machine

Rib Spine Lung

Heart Diaphragm

Beam of

X-rays

X-ray film in

cassette

CHEST X-RAY PROCEDURE

CHEST X-RAY IMAGE

Adjustable
stand