On imaging exactness in digital subtraction angiography

In digital subtraction angiography (DSA), the spatial resolution capacity is considerably influenced by the concentration of contrast medium. Studies in vascular models showed that in intravenous DSA (IV-DSA) the concentrations of contrast medium are not sufficient to depict minor lesions of the vascular walls. Under the conditions of intraarterial DSA (IA-DSA), the imaging exactness increases considerably. Minimal lesions may rather be detected in front or rear walls than in the marginal parts of the vessels. This is the field in which digital and conventional angiography differ considerably. In pulsating vessels, imaging quality requires the greatest possible difference between the video signal of the applied contrast medium and the noise of the motion artifact. Whereas in IV-DSA minor alterations of the vascular wall are masked by pulsatory movements, the increased concentrations of contrast medium used in IA-DSA are sufficient for detecting e.g. membrane stenoses of 1 mm breadth. Nonionic contrast media differ from conventional contrast media, among other things, by their increased viscosity. This causes flow artifacts which are less marked if the contrast medium is diluted to values usual in IA-DSA. (orig./HP)