Digital subtraction angiography

The Digital subtraction angiography ( DSA) is a form of angiography, so is used to examine blood vessels. Their advantage over the so-called conventional sheet film angiography is that " disturbing " image aspects are invisible by the subtraction. The DSA, a method of projection, which competes with magnetic resonance angiography, computed tomography angiography and ultrasound.

Here, the body part to be examined, such as the brain, creates multiple temporally successive images. During the recording sequence, a contrast agent is injected into venous sinuses. This results in a recording without contrast agent, also referred to as a mask, and other images with contrast distribution. The digital mask image is subtracted from the subsequent images. It leaves only the parts of the image that are different, which is exactly the blood vessels. By creating multiple images at different time points following on a mask image, film-like image sequences can be created. Also, a color-coded representation is possible by the gray level curves for the image pixel color values ​​are mapped to.

The contrast agent used in this case is indeed usually contains iodine ( iodine as well contrasts, due to its high radiation density); in renal failure patients, however, can also be used a "negative contrast agents ". Isotonic saline, although only less dense than blood, but contrasts well. There is even a procedure in which CO2 ( about 10-20 ml gas) is introduced into the femoral artery, which will then represent the vessels very clearly hypodense.