Angiography is a special form of x-ray examination
that shows the shape of the blood flow in
arteries and veins. A special dye is injected
into the bloodstream which shows up when
the x-ray is taken. Angiography shows whether
blood vessels are narrow, irregular or blocked.
It detects any diseases that change the
appearance of the blood vessel channel such
as atherosclerosis, which causes fatty plaques
to be deposited in the lining and narrows
the vessel. It shows up blood clots (thrombosis)
which can block vessels, and local ballooning
of the vessel itself (aneurysm).
Angiography can also
detect the development of clumps of new
vessels and other abnormal patterns that
suggest tumours or injury to organs.
Angiography is especially
important in investigating the state of
the arteries supplying the brain, and the
presence of abnormal arteries in and around
the brain. Angiography is used most often
to check the state of the coronary arteries
of the heart. In this case it is used to
identify the sites of narrowing or blockage
in arteries, so that these may be treated
by balloon angioplasty or, if necessary,
by a coronary artery bypass operation.
Why it is necessary
The state of your
arteries has a large bearing on your health.
Arteries supply the blood that keeps all
parts of your body alive and working. Any
defect in the arteries can seriously affect
the part that the arteries supply. This
applies to the brain, the heart, the limbs
and the internal organs. Serious arterial
disease that limits the blood supply to
these parts can cause strokes, heart attacks,
tissue death (gangrene) and failure of organs
to work properly.
Knowledge of the state
of the arteries and veins helps decide the
best treatment option.
How it is performed
Angiography involves
the insertion of a fine soft tube, called
a catheter, into the blood vessel to be
examined. This is done under a local anaesthetic.
The catheter is inserted either at the front
of the elbow, for investigation of the neck
arteries (a carotid angiogram), or in the
groin for a coronary angiogram. A long,
thin guide wire with a smooth rounded tip
is first inserted and then guided, under
X-ray control using a fluorescent screen
or a TV image intensifier, into the vessel
to be examined.
When the wire is in
place the catheter is slipped over it and
pushed along until its tip is in the right
position. The wire is now removed and the
contrast fluid injected into the catheter.
The image can be viewed on the screen and
a video film can be made from this. Alternatively,
a rapid sequence of x-ray pictures may be
taken and the flow along the vessel studied
by comparing these.
Digital-subtraction
angiography is a method of producing a detailed
image of blood vessels that eliminates unwanted
surrounding detail. Two digitised images
are made, one before and one after injecting
a dye that is opaque to X-rays and that
circulates in the blood. One of these is
then turned into a negative and the two
are combined.
Everything except
the differences between the two have now
been eliminated, so only the shape of the
blood content of the vessels is visible.
This provides a useful representation of
the interior of the arteries and veins.
A special form of
angiography used by eye doctors is called
fluorescein angiography. It is used to examine
the state of the tiny arteries lying on
the retinas on the inside of the back of
the eyes.
In this case the dye
used shines brightly in violet light and
can be seen clearly when the eye is examined
with an ophthalmoscope. In practice, the
dye is injected and then a series of photographs
of the retinas are taken.
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Angiography
