How is it performed? of Angiography

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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.