What is a CT angiogram?
A CT angiogram is a diagnostic test that uses X-rays and an injected dye to produce 3-dimensional images of the blood vessels and surrounding tissues. The test does not require entering the body (it is noninvasive).
A CT can determine the location and severity of artery narrowing or blockages caused by:
- PAD in the legs
- Kidney artery disease
- Carotid (neck) artery disease
- Aortic disease
See also: CT scan for Stroke Diagnosis
Who might have a CT angiogram?
If you have been diagnosed with PAD using another test (such as an Ankle-Brachial Index or Pulse Volume Recording), your doctor may ask for a CT angiogram to get a closer look at your arteries. The CT angiogram provides more detailed information than a duplex ultrasound, but is not as detailed as contrast angiography, the gold-standard test for examining artery disease.
CT angiography is most often used in women who are considering a procedure to restore blood flow to arteries that have been narrowed by PAD, such as angioplasty and stents or lower extremity bypass surgery. The detailed images produced by the CT angiogram allow doctors to determine which procedure may be best for you, develop a plan to treat the blockages, and monitor you after the treatment.
A CT angiogram can also be used to diagnose and monitor aortic aneurysms. The test can also be used to look at the pulmonary arteries in the lungs in women who have symptoms of pulmonary embolism, a blood clot that formed in the deep veins of the legs (DVT) and traveled to the lungs.
Although a magnetic resonance angiogram (MRA) is a more established test for PAD that provides similar information as a CT angiogram, the CT angiogram is becoming more widely used and is an accurate and reliable test. See How does a CT angiogram compare to other imaging tests?
How does a CT angiogram work?
During a CT scan a beam of X-rays is sent towards your body in a 360-degree circle. Detectors pick up the X-rays after they have passed through your body, creating digital images of thin “slices” of your body. A computer assembles these slices into a complete 3-dimensional picture of the arteries and surrounding tissues. A special iodine-based contrast dye is injected into your bloodstream to highlight the arteries, which do not appear on a normal X-ray.
A 3-D CT angiogram of the body (other tissues have been digitally removed)
How do I prepare for a CT angiogram?
You should not to eat or drink for 4 to 8 hours before the test. You may be asked to change into a hospital gown, and will need to remove all metallic items including jewelry, eyeglasses, hearing aids, and removable dental work, which can affect the quality of the images.
Before you have the test, be sure your doctor knows if you:
- Are allergic to any medications
- Are allergic to the iodine dye used in the test
- Have ever had a serious allergic reaction (anaphylaxis) to any substance
- Have a history of kidney problems
- Have diabetes
- Are pregnant or breastfeeding (you should not resume breastfeeding until the dye has been cleared from your body)
What happens during the test?
You will lie face up on a table (sometimes on your side or stomach). An intravenous (IV) line will be inserted into a small vein in your hand or arm, which is used to inject the contrast dye used during the test. You may experience a warm, flushed sensation as the dye is injected and a metallic taste in your mouth. If you are having a CT angiogram of the aorta, small sticky pads may be attached to your chest to monitor your heart rate with an ECG machine.
A CT Scanner
It is important that you remain absolutely still to get the best quality image, so straps and pillows may be used to help you maintain the correct body position. A CT scanner is open; only the part of the body being examined lies inside the machine.
You will be alone in the exam room during the scan; however, the technician will be able to see you through a window from an adjacent room and hear and speak with you through a two-way intercom.
The test will begin and the table will move rapidly through the scanner as the machine takes a picture of different “slices” of your body. The technician may ask you to hold your breath for 10 to 20 seconds at certain times, since even the motion of breathing can interfere with getting the best images.
A CT angiogram typically takes less than 30 minutes, including preparation time. The scan itself usually takes only a few minutes.
What happens after the test?
When the test is complete, your intravenous (IV) line will be removed and the images will be sent to a radiologist to be analyzed. Your doctor will discuss the results with you.
You can resume your treatment or normal activities immediately after a CT angiogram. Be sure to drink plenty of fluids to help flush the dye from your system. Nursing mothers should wait 36 to 48 hours before breastfeeding to allow the dye to pass through their system. You may want to save up breast milk before the test, and pump and discard all milk produced in the first few days after the test. Your doctor may give you other special instructions.
If you experience flushing (skin redness), itching, or difficulty breathing or swallowing after the test, these may be signs of an allergic reaction to the contrast dye. Tell the doctor or technician immediately if you experience any of these signs. If you have already left the hospital or testing facility and experience any of these symptoms, call 9-1-1 or have someone take you to the nearest emergency room immediately a reaction to the dye can be serious and even life threatening if not treated promptly.
What do the results mean?
The images produced by a CT angiogram allow doctors to detect narrowing or blockages in your blood vessels caused by PAD. In a normal CT angiogram, the dye will fill the arteries completely, causing them to appear white on the final image. Areas where the dye flows in a thinner stream or stops flowing indicate locations where PAD is interfering with blood flow.
A 3-D CT angiogram image of the legs in a patient with PAD.
Note the extensive notches in thigh arteries.
If you have a CT angiogram to look for an aortic aneurysm, doctors will look for places where the dye has entered the wall of the aorta, or filled up a balloon-like bulging out of the artery wall.
How accurate is a CT angiogram?
The CT angiogram is an accurate and reliable test for diagnosing and investigating PAD. A large analysis of 12 studies that included 436 PAD patients (24% were women) found that CT angiography was about 92% accurate at diagnosing PAD in the aorta, abdomen, and legs. CT angiogram technology continues to improve, and the latest studies find the test can be up to 98% accurate.
How does a CT angiogram compare to other imaging tests?
Click here for a quick comparison of the CT angiogram with other imaging tests used to diagnose and evaluate PAD.
The gold-standard test for looking at the structure of the arteries is a contrast angiogram. Compared to a contrast angiogram, a CT angiogram produces images that are slightly less detailed. Because the dye used in a CT scan flows through the entire body, dye in the veins can sometime block a view of the arteries on the CT image.
However, studies have shown that a CT angiogram is accurate enough to diagnose PAD and plan treatments. The test has several advantages over a conventional angiogram. A CT angiogram does not require entering the body, whereas a conventional angiogram involves the insertion of a long thin tube (called a catheter) into the arteries to inject the dye directly. In addition, the 3-dimensional CT images can provide a better view of certain narrowings. Because a CT angiogram also produces pictures of the surrounding tissues, it can detect some aneurysms and other problems that may be missed on a contrast angiogram, which shows only the arteries.
As a less-invasive test for planning PAD treatments, the main alternative to a CT angiogram is a magnetic resonance angiogram (MRA), which has been more studied and is more widely used. Both tests are more detailed than a duplex ultrasound test, and they are also more expensive and may take longer to perform. A CT angiogram requires exposure to radiation and an iodine-based contrast dye. MRA does not involve radiation and uses a dye that is less likely to cause an allergic reaction or kidney damage.
CT angiogram has some advantages over MRA. It provides more detail and can be performed more quickly. Because the CT machine is more open, the test experience may be more pleasant for women with a fear of enclosed spaces (claustrophobia) than the closed design of an MR imaging machine. CT angiograms can also be used safely in women who cannot have an MRA test because of metal implants like pacemakers or defibrillators. Smaller metallic implants like stents cause less of a disturbance on the CT image than they do on an MR image. CT angiograms are more accurate than MRA in patients with arteries that have been hardened by a buildup of calcium, which often occurs in women with diabetes.
In most cases, a CT angiogram, MRA, and a contrast angiogram provide the same information, and the choice of test depends on which are available at your hospital, what your doctor is most comfortable with, and your personal preferences.
What are the risks of the test?
The CT angiogram is a safe and painless procedure. Although it is rare, some people have an allergic reaction to the dye used in the test. Be sure to tell your doctor ahead of time if you have experienced this in the past medications can be given during the procedure to minimize the risks.
Because X-rays are used to produce an image, CT scans expose you to some radiation. Technicians are trained to minimize your radiation exposure, and the amount of radiation you are exposed to during diagnostic tests is considered safe. A CT angiogram involves less radiation exposure than a contrast angiogram. If you are concerned about radiation exposure, talk to your doctor about the risks and benefits of the test.