Radiographic technique for imaging blood vessels. In classic methods, the vessels of the brain are visualized by injection of radiopaque dye. Digital subtraction angiography (using computer processing to produce images) carries less risk for the patient because the amount of dye can be reduced. Computerized tomography and magnetic resonance angiography (CTA and MRA) are less invasive means of visualizing extracranial and large intracranial vessles. However, at present, invasive angiograpy is more sensitive for smaller vessels.