![Abdominal CT angiography](https://upload.wikimedia.org/wikipedia/commons/a/a1/Abdominal_CT_angiography.jpg)
Computed tomography angiography (also called CT angiography or CTA) is a
computed tomography technique used for
angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
—the visualization of
arteries
An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
and
veins
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...
—throughout the
human body
The human body is the structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently organ systems. They ensure homeostasis and the life, viabi ...
. Using contrast injected into the blood vessels, images are created to look for blockages,
aneurysm
An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (s ...
s (dilations of walls),
dissections
Dissection (from Latin ' "to cut to pieces"; also called anatomization) is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in pathology and forensic medicine to determine the cause of ...
(tearing of walls), and
stenosis
A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture).
''Stricture'' ...
(narrowing of vessel). CTA can be used to visualize the vessels of the heart, the aorta and other large blood vessels, the lungs, the kidneys, the head and neck, and the arms and legs. CTA can also be used to localise arterial or venous bleed of the gastrointestinal system.
Medical uses
CTA can be used to examine blood vessels in many key areas of the body including the brain, kidneys, pelvis, and the lungs.
Coronary CT angiography
Coronary CT angiography
Coronary CT angiography (CTA or CCTA) is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The patient receives an intravenous injection of radiocontrast and then the heart is scanned using a high spee ...
(CCTA) is the use of CT angiography to assess the
arteries
An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
of the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
. The patient receives an
intravenous injection
Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutri ...
of
contrast and then the heart is scanned using a high speed
CT scanner. With the advances in CT technology, patients are typically able to be scanned without needing medicines by simply holding their breath during the scan. CTA is used to assess heart or vessel irregularities, location of stents and whether they are still open, and occasionally to check for atherosclerotic disease.
This method displays the anatomical detail of blood vessels more precisely than
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
(MRI) or
ultrasound
Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
. Today, many patients can undergo CTA in place of a conventional
catheter
In medicine, a catheter (/ˈkæθətər/) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Cath ...
angiogram
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
, a minor procedure during which a catheter is passed through the blood vessels all the way to the heart. However, CCTA has not fully replaced this procedure. CCTA is able to detect narrowing of blood vessels in time for corrective therapy to be done. CCTA is a useful way of screening for arterial disease because it is safer, much less time-consuming than catheter angiography, and is also a cost-effective procedure.
Aorta and great arteries
CTA can be used in the chest and abdomen to identify
aneurysm
An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (s ...
s in the aorta or other major blood vessels. These areas of weakened blood vessel walls that bulge out can life-threatening if they rupture. CTA is the test of choice when assessing aneurysm before and after endovascular stenting due to the ability to detect calcium within the wall.
Another positive of CTA in abdominal aortic aneurysm assessment is that it allows for better estimation of blood vessel dilation and can better detect blood clots compared to standard
angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
.
CTA is used also to identify
arterial dissection, including
aortic dissection
Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or ...
in the
aorta
The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...
or its major branches. Arterial dissection is when the layers of the artery wall peel away from each other; this causes pain and can be life-threatening. CTA is a quick and non-invasive method of identifying dissections and can show the extent of the disease and if there is leakage.
Pulmonary arteries
CT pulmonary angiogram
A CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography (CT) angiography to obtain an image of the pulmonary arteries. Its main use is to diagnose pulmonary embolism (PE). It is a preferred choice of imaging i ...
(CTPA) is used to examine the pulmonary arteries in the lungs, most commonly to rule out
pulmonary embolism
Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...
(PE), a serious but treatable condition. It has become the technique of choice for detection of pulmonary embolism due to its wide availability, short exam time, ability to see other diseases that may present like pulmonary embolisms, and a high degree of confidence in the validity of the test.
In this test, a PE will appear as a dark spot inside the blood vessel or a sudden stop of the bright contrast material.
CT angiography should not be used to evaluate for
pulmonary embolism
Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...
when other tests indicate that there is a low probability of a person having this condition.
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D-dimer
D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is so named because it contains two D fragments of the fibrin protein joined by a cross ...
assay might be a preferred alternative to test for pulmonary embolism, and that test and a low clinical prediction score on the
Wells test or
Geneva score
The Geneva score is a clinical prediction rule used in determining the pre-test probability of pulmonary embolism (PE) based on a patient's risk factors and clinical findings. It has been shown to be as accurate as the Wells Score, and is less rel ...
can exclude pulmonary embolism as a possibility.
Renal arteries
![CTA FMD](https://upload.wikimedia.org/wikipedia/commons/8/89/CTA_FMD.jpg)
Visualization of blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders can be performed using CTA. Stenosis (narrowing) of a renal artery is a cause of
hypertension
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
(high blood pressure) in some patients and can be corrected. A special computerized method of viewing the images makes renal CT angiography a very accurate examination. CTA is also used in the assessment of native and transplant renal arteries.
While CTA is great for imaging of the kidneys, it lacks the ability to perform procedures at the same time. Thus traditional catheter angiography is used in cases of acute renal hemorrhage or acute arterial obstruction.
Carotid, vertebral and intracranial vessels
![CT angiography of a vascular malformation with intraventricular hemorrhage](https://upload.wikimedia.org/wikipedia/commons/4/41/CT_angiography_of_a_vascular_malformation_with_intraventricular_hemorrhage.png)
CTA can be used assess acute stroke patients by identifying clots in the arteries of the brain.
It can also be used to identify small aneurysms or
arteriovenous malformation
Arteriovenous malformation is an abnormal connection between arteries and veins, bypassing the capillary system. This vascular anomaly is widely known because of its occurrence in the central nervous system (usually cerebral AVM), but can appea ...
inside the brain that can be life-threatening. While CTA can produce high quality images of the
carotid arteries
In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
stenosis
A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture).
''Stricture'' ...
(narrowing of the vessel), calcium deposits (calcified plaques) in the area where the vessels split can lead to interference with accurate stenosis grading. Because of this,
magnetic resonance angiography
Magnetic resonance angiography (MRA) is a group of techniques based on magnetic resonance imaging (MRI) to image blood vessels. Magnetic resonance angiography is used to generate images of arteries (and less commonly veins) in order to evaluate t ...
is used more often for this purpose.
Peripheral arteries
CTA can be used in the legs to detect atherosclerotic disease that has narrowed the arteries. It can also be used to image vessels in suspected blockages, trauma cases, or patients with surgical complications.
Technique
![CT angiography of the head without and with bone removal](https://upload.wikimedia.org/wikipedia/commons/9/95/CT_angiography_of_the_head_without_and_with_bone_removal.jpg)
CT angiography is a
contrast CT
Contrast CT, or contrast enhanced computed tomography (CECT), is X-ray computed tomography (CT) using radiocontrast. Radiocontrasts for X-ray CT are generally iodine-based types. This is useful to highlight structures such as blood vessels that ...
where images are taken with a certain delay after injection of
radiocontrast
Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically io ...
material. The contrast material is
radiodense
Radiodensity (or radiopacity) is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is, the relative inability of those kinds of electromagnetic radiation to pass through a particular material. Radiolucency or hypod ...
causing it to light up brightly within the blood vessels of interest. In order for the CT scanner to be able to scan the correct area where the contrast is, the scanner uses either automatic detectors which start scanning when enough contrast is present, or small test boluses. With the small test bolus, a small amount of contrast is injected in order to detect the speed that the contrast will move through the blood vessels. After determining this speed, the full bolus is injected and the scan is begun at the timing determined by the test bolus. After the scan is completed the images are post-processed to better visualize the vessels and can even be created in the 3D images.
Risks
Harms of overuse of CT angiography include radiation exposure and the possibility of finding then seeking treatment for a clinically insignificant pulmonary embolism which ought not be treated.
Adverse reactions
A reaction may occur whenever iodine contrast is injected. These reactions range in severity and it is difficult to predict if they will occur. With the current practice of using low-osmolar contrast these adverse reactions only occur in ~0.1% of cases.
The severity of the reaction can be broken down into three groups:
* Mild - no treatment required: nausea, vomiting, and/or
hives
Hives, also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. Hives may burn or sting. The patches of rash may appear on different body parts, with variable duration from minutes to days, and does not leave any long-lasti ...
.
* Moderate - requires treatment: severe hives, lightheadedness or brief loss of consciousness, mild
bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release (degranulation) of substances from mast cells or basophils under the influence of anaphylatoxins. It causes di ...
, and/or increased heart rate.
* Severe - requires immediate treatment: severe
bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release (degranulation) of substances from mast cells or basophils under the influence of anaphylatoxins. It causes di ...
, throat swelling, seizure, severe low
blood pressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
, and/or cardiac arrest.
A patient with a history of allergy to contrast may be advised to take medications such as corticosteroids or histamine (H1) blockers before CTA to lessen the risk of allergic reaction or to undergo a different exam that does not call for contrast material injection.
Patients should also be well hydrated in order to minimize possible adverse effects of contrast.
Contrary to popular belief there is no correlation between seafood allergies and reactions to iodine contrast, as shown by many recent studies.
Kidneys
Historically it has been thought that contrast material can lead to
contrast-induced nephropathy
Contrast-induced nephropathy (CIN) is a purported form of kidney damage in which there has been recent exposure to medical imaging contrast material without another clear cause for the acute kidney injury.
Despite extensive speculation, the actua ...
(also called CIN) in any patient. However, recent studies have shown that the risk of kidney injury caused by contrast agent in patients with no history of kidney problems occurs extremely infrequently.
The use of CTA in people with
kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, kidney disease or long-standing severe diabetes should be weighed carefully as the use of IV iodine contrast material may further harm kidney function. The decision not to use contrast agents must be weighed against the possibility of misdiagnoses if contrast is not used.
Radiation
Compared with other imaging modalities, CTA is associated with a significant dose of ionizing radiation. Varying significantly with patient age, sex, and exam protocol, radiation risk models predict coronary CTA to increase lifetime cancer risk. The radiation risk presented by CTA is much lower than invasive angiography procedures.
CT angiography should not be performed in patients who are pregnant as the contrast and radiation may lead to harm to the fetus. The extent of harm to the fetus has not been fully determined.
History
By 1994 CT angiography began to replace conventional angiography in diagnosing and characterizing most cardiovascular abnormalities.
Prior to this, conventional angiography had been in use for 70 years.
See also
*
Angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
*
Magnetic resonance angiography
Magnetic resonance angiography (MRA) is a group of techniques based on magnetic resonance imaging (MRI) to image blood vessels. Magnetic resonance angiography is used to generate images of arteries (and less commonly veins) in order to evaluate t ...
References
{{Medical imaging
X-ray computed tomography