Digital subtraction angiography (DSA) is a method of visualizing the vessels of the body with the intravenous injection of contrast material. Improvements in computers, television systems, and image intensifiers have contributed to the increased image quality of DSA. With DSA, the vessels such as the carotid bifurcations and the intracranial vasculature can be visualized with a 2-3% concentration of contrast material, while with conventional angiography, the concentration of contrast in vessels is 40-50%. Using IV DSA, visualization of the carotid bifurcations is of good or excellent quality 85% of the time. In a high percentage of these cases, IV DSA replaces conventional angiography, although for imaging of the intracranial vessels, IV DSA is not as good as conventional angiography. In most tumor patients, however, conventional intracranial angiography is not needed because IV DSA combined with computed tomography gives sufficient information.