7. Digital subtraction arteriogram (DSA) — aortic arch, LAO projection

For a digital subtraction arteriogram, a digital image of the region is created both before and after the injection of contrast into the appropriate blood vessel. The first image is then digitally subtracted from the second, leaving only the image of the contrast-filled blood vessels, which is usually displayed as a positive print of the traditional radiographic image.

Because the orientation of the aortic arch in the mediastinum is from anterior on the right to posterior on the left, it is seen with less foreshortening on the left anterior oblique projection than it would be on the PA projection.

Note that the first two branches of the aorta, the coronary arteries, are not visualized on this study.