What is angiography?
Angiography (angio) is visualisation of a blood vessel with or without injecting a contrast (‘dye’) into its lumen. Most of us are now familiar with coronary angio used to visualise the blood vessels supplying oxygenated blood to the heart. Usually visualization of each blood vessel is named after it: e.g. renal angio – visualisation of renal (kidney) vessels; cerebral angio – visualization of blood vessels of cerebral (brain) vessels; peripheral angio – visualisation of the blood vessels of the limbs and other peripheral organs.
What are the different techniques of angiography?
Angiography can be divided into invasive and non invasive depending how much invasion is done into the body structures for visualising the vessels. Magnetic resonance angio (MR angio) can be considered as the truly non invasive angiography as there is no need to inject any contrast into the blood vessel to visualize the vessels. The hydrogen ions in the water content itself acts as the contrast for MR angio. Hence MR angiography is also known as ‘dyeless angiography‘. In computed tomographic (CT) angio, iodinated contrast is injected into the peripheral veins (blood vessels carrying deoxygenated blood to the heart) of the forearms. X-ray equipment then captures the movement of the contrast into various parts of the body. If if captures the coronary blood vessels, then it is called CT coronary angio. If it captures the blood flow to the lungs, it is called CT pulmonary angio. In truly invasive angio like coronary angio, the contrast is injected directly into the blood vessels of the heart (coronary arteries). This is done by introducing small tubes known as catheters under local anaesthesia through the blood vessels at the wrist or groin and tacking them under X-ray fluoroscopic guidance to the coronary arteries through the aorta (largest blood vessel carrying oxygenated blood, arising from the heart).
What is fluorescein angiography?
Fluorescein angiography is used to visualise the blood vessels of the eye by injecting fluorescent dye into the blood vessels. The images of the inner eye are then photographed, to study the blood vessels of the retina, the light sensitive inner coating of the eye which senses our visual information and transmits it to the brain.