Computed tomography angiography

Computed tomography angiography (CTA) is a computed tomography technique used to visualize arterial and venous vessels throughout the body. This ranges from arteries serving the brain to those bringing blood to the lungs, kidneys, arms and legs.

Technique
CT combines the use of x-rays with computerized analysis of the images. Beams of x-rays are passed from a rotating device through the area of interest in the patient's body from several different angles to obtain projection images, which then are assembled by computer into a three-dimensional picture of the area being studied.

The scan is performed simultaneously with a high speed contrast media injection using a technique called Bolus Tracking. Compared to catheter angiography, which involves placing a sizable catheter and injecting contrast material into a large artery or vein, CTA is a much less invasive and more patient-friendly procedure. The contrast material is injected into a small peripheral vein by using a small needle or cannula. This type of exam has been used to screen large numbers of individuals for arterial disease.

Clinical Applications
CTA is commonly used to:
 * Examine the pulmonary arteries in the lungs to rule out pulmonary embolism, a serious but treatable condition. This is called a CTPA.
 * Visualize blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders. Narrowing (stenosis) of a renal artery is a cause of high blood pressure (hypertension) in some patients and can be corrected. A special computerized method of viewing the images makes renal CT angiography a very accurate examination. Also done in prospective kidney donors.
 * Identify aneurysms in the aorta or in other major blood vessels. Aneurysms are diseased areas of a weakened blood vessel wall that bulges out—like a bulge in a tire. Aneurysms are life-threatening because they can rupture.
 * Identify dissection in the aorta or its major branches. Dissection means that the layers of the artery wall peel away from each other—like the layers of an onion. Dissection can cause pain and can be life-threatening.
 * Identify a small aneurysm or arteriovenous malformation inside the brain that can be life-threatening.
 * Detect atherosclerotic disease that has narrowed the arteries to the legs.
 * Detect thrombosis (clots) in veins, for example large veins in the pelvis and legs. Such clots can travel to the lungs and result in pulmonary embolism.

CTA is also used to detect narrowing or obstruction of arteries in the pelvis and in the carotid arteries,which bring blood from the heart to the brain. When a stent has been placed to restore blood flow in a diseased artery, CTA will show whether it is serving its purpose. Examining arteries in the brain may help reach a correct diagnosis in patients who complain of headaches, dizziness, ringing in the ears or fainting. Injured patients may benefit from CTA if there is a possibility that one or more arteries have been damaged. In patients with a tumor, it may be helpful for the surgeon to know the details of arteries feeding the growth.

Benefits and Risks
Benefits
 * CTA can be used to examine blood vessels in many key areas of the body, including the brain, kidneys, pelvis, and the lungs. The procedure is able to detect narrowing of blood vessels in time for corrective therapy to be done.
 * This method displays the anatomical detail of blood vessels more precisely than magnetic resonance imaging (MRI) or ultrasound. Today, many patients can undergo CTA in place of a conventional catheter angiogram.
 * CTA is a useful way of screening for arterial disease because it is safer and much less time-consuming than catheter angiography and is a cost-effective procedure. There is also less discomfort because contrast material is injected into an arm vein rather than into a large artery in the groin.

Risks
 * There is a risk of an allergic reaction, which may be serious, whenever contrast material containing iodine is injected. A patient with a history of allergy to x-ray dye may be advised to take special medication for 24 hours before CTA to lessen the risk of allergic reaction or to undergo a different exam that does not call for contrast material injection.
 * CTA should be avoided in patients with kidney disease or severe diabetes, because x-ray contrast material can further harm kidney function.
 * If a large amount of x-ray contrast material leaks out under the skin where the IV is placed, skin damage can result.