ABSTRACT
Digital subtraction angiography (DSA) involves computer enhancement to produce arterial images (see Figure 5.6a-d) from an intravenous injection or a very small intra-arterial injection. An X-ray picture is taken of a patient immediately prior to an injection of contrast material. The image is recorded on a computer in digital form. An intravenous injection of contrast material is given. This travels first to the heart, then through the lungs, before being pumped through the arterial system. The contrast material will eventually be cleared but, prior to this, it becomes distributed, first throughout the whole arterial system and then throughout the arterial and venous system. If a further X-ray picture is taken to coincide with the contrast material arriving in the arterial circulation (a few seconds after injection), then this picture can be stored in the computer too. If the computer then subtracts the first image from the second image, all that is left is the contrast material, the contrast material being the only difference between the first and the second image. It is then possible to enhance this image, giving an outline of the arterial tree. The resolution is very good and may avoid the need for a direct arterial puncture. If particularly good quality images are required, then a small intra-arterial injection using a fine needle and a small volume of contrast material will achieve this. All arteries in the body, including those in the lungs and the brain, can be imaged in this way.
Figure 5.6a Digital subtraction angiogram, showing aorto-iliac vessels
