angiography

n.

imaging of blood vessels (see also coronary angiography, lymphangiography). Fluoroscopic angiography is performed by injection of contrast medium during X-ray fluoroscopy. Positive (radiopaque) contrast medium containing iodine or, more recently, negative (radiolucent) gas (carbon dioxide) may be used. Digital subtraction increases the visibility of the vessels. Magnetic resonance angiography (MRA) can be performed either by injection of a magnetic resonance contrast agent (see contrast medium), which gives an increased signal from the blood, or by relying on the movement of blood to give a lack of signal in the plane being examined. These images can be reconstructed in two or three dimensions. Computerized tomographic angiography (CTA) uses a radiographic contrast agent, usually injected into a vein, to enhance the density of the blood. This can then be clearly seen on either two- or three-dimensional images, with other surrounding tissues hidden by the computer. Fluorescein angiography is a common method of investigation in ophthalmology. Fluorescein sodium is injected into a vein in the arm, from which it circulates throughout the body. Light of an appropriate wavelength is shone into the eye, causing the dye in the retinal blood vessels to fluoresce. This allows the circulation through the retinal blood vessels to be observed and photographed. Indocyanine green (ICG) angiography, using a newer dye, gives much better visualization of the choroidal circulation. It is particularly useful for visualization and treatment of choroidal neovascular membranes (see neovascularization).