What is CT Angiography?

Overview

Computed tomography angiography (CTA) is a medical imaging technique that combines the principles of a computed tomography (CT) scan with angiography. Angiography is a type of X-ray used to assess the health of your blood vessels, involving the injection of a special dye, known as a contrast agent. A contrast agent is used in CTA to highlight your blood vessels and tissues that would otherwise not appear in a traditional  X-ray. The contrast agent used in X-ray-based imaging methods is typically iodine-based, which improves the quality of images taken during the scan. 

CTA may help diagnose and evaluate vascular diseases (i.e. diseases that affect blood vessels) and other related conditions. A CTA to assess the heart and it’s blood vessels is called a CT coronary angiogram (CTCA). 

This article will explain when CTAs are required and details of the procedure. This includes how it works, what you can do to prepare, what to expect during and following the imaging, and its benefits and risks.

Why might I need a CTA? 

Checking for the narrowing or blockage of arteries is a common reason physicians order  CTAs. You may also be referred to have a CTA to help diagnose any condition relating to your blood vessels. Information provided by a CTA may help prevent heart attacks or strokes.

CTA is commonly used to identify size, location, and severity in the following:

• Aneurysms - Aneurysms are enlarged blood vessels that are at risk of rupturing and causing life-threatening internal bleeding
• Atherosclerosis - Atherosclerosis is the thickening of the arteries due to the accumulation of fatty material which forms plaque in the arterial walls. This reduces blood flow and oxygen supply to organs and tissues
• Coronary Artery Disease (CAD) - CAD occurs when atherosclerosis blocks your heart's blood supply. CAD may be accompanied by angina (chest pain) and shortness of breath which may prompt your doctor to refer you for a CTA¹
• Pulmonary embolism - Blood clots that may have formed in the veins of your legs can travel to your lungs, causing a blockage that can be life-threatening. In this case, computed tomography pulmonary angiography (CTPA) is used as a first-line diagnostic tool due to its high sensitivity and accuracy² 
• Tears or ruptures in the blood vessels
• Blood vessel abnormalities in the brain which may cause a stroke
• Identify blood vessels damaged by injury
• Tumours - CTA is frequently used to evaluate soft tissue masses in the lower body, where it can differentiate between benign and malignant tumours based on the number of feeding arteries³ 

CTA can also be used to check blood vessels before and after surgery, to identify abnormalities and prevent complications. For example, it is commonly used by surgeons in preparation for a kidney transplant as it provides precise anatomy of the renal structure.⁴

CTA Procedure

Preparing for a CTA

CTA is typically performed by doctors who specialise in taking and interpreting imaging scans, known as radiologists. They will give you guidance on how to prepare for a CTA based on your conditions. Guidance may involve the following: 

• Precaution - It is important to inform your doctor if you are pregnant or think you may be pregnant. This is because an unborn baby has a one in 1,000 chance of developing cancer as a child if exposed to radiation in CTA, and other options may be discussed with you.
• Clothing - Wear loose-fitting and comfortable clothing to the examination as you may be asked to change into a provided patient gown for the procedure. All metal objects must be removed as they can appear in CTA images and obstruct adjacent organs.⁵ These include jewellery, glasses, dentures, piercings and bras containing metal underwire.
• Fasting - Due to the use of a contrast agent during the scan, you may be instructed not to eat or drink anything for a few hours prior which improves the quality of images produced. However, you may still be able to drink clear liquids. If you are diabetic, you may be instructed to eat a light meal a few hours before the scan.
• Allergies - Inform your doctor in advance about any allergies you may have. If you have a known allergy to the contrast agent, a steroid may be prescribed to reduce the risk of an allergic reaction.
• Recent illnesses - Certain health conditions can increase the risk of an adverse reaction during a CTA. These include a history of heart disease, diabetes, asthma and kidney disease.
• Medications - You should review your current medications with your doctor to ensure they are safe to be taken before and after a CTA. You might be asked to stop taking certain medications if they are known to interfere with the contrast agent used or affect blood clotting.

How does the CTA procedure work?

The CT scanner is a large machine that encompasses a short tunnel with a narrow examining table that passes through it to allow different body areas to be examined. The X-ray detectors are located in the machinery around you and rotate during the scan. During the exam, you will be alone in the room as the imaging information is processed in a separate room where a radiologist will speak to you. 

During the scan, X-ray sources release small high-energy X-ray beams through the body. The rays that are released out of the body are captured by the X-ray detectors and processed by a computer to produce images.⁶ Many scans are taken so that the data can be used to create 3D images of the structures within the body. 

Iodinated contrast agents are used as they allow scattering and absorption of energy through the tissues, reducing the amount of radiation reaching the detector. This creates contrast on the X-ray images and is vital in defining structures.⁷

What to expect during a CTA 

During a CTA examination, you can expect:

• To be positioned lying flat on your back on the examination table. Straps and pillows are sometimes used to maintain the correct position and to help remain still. 
• The contrast agent will be injected into your hand or arm via an automatic intravenous (IV) injection pump. You may feel a metallic taste and a warm sensation at this point.
• The radiologist will leave the room just before the examination table moves through the scanner.
• During the scan, the scanner will rotate around you and you may hear buzzing sounds. You may also be asked to hold your breath during scanning as any motion can cause blurring in produced images, delaying the process.
• One scan takes a few minutes but can take longer if multiple scans are required.
• The radiologist will ensure that the scans are of an acceptable quality to be interpreted, otherwise, you may have to repeat the process. 

The CTA itself is non-invasive and painless, however, you may have discomfort from the injection of the contrast agent or feel claustrophobic

What happens after a CTA?

After the scan, the IV will be removed and a dressing is placed at the site of injection. You may be asked to drink plenty of water to flush out the contrast agent from your system. Unless given specific instructions after the test, you can resume normal activities. 

Results and follow-up

CTA test results are usually reviewed a few days or weeks after the procedure with you by your doctor. Depending on the results, follow-up tests may be required and treatment plans discussed. 

Benefits and Risks of a CTA

CTA tests are safe for most people with no adverse effects. The benefits of CTA outweigh the risks, particularly when it comes to diagnosing vascular or cardiovascular diseases. 

Benefits

• CTA can eliminate the requirement for surgery, or if necessary, can allow surgery to be performed more accurately.⁶
• It can provide more precise anatomical details than standard angiography and magnetic resonance imaging (MRI).
• It is a fast and non-invasive imaging method, reducing the risk associated with invasive techniques.
• No radiation remains in your body after the scan.
• The X-rays used in CTA generally do not have immediate side effects.

Risks

• Although exposure to radiation in a single CTA is low, there is always a chance of developing cancer from excessive exposure.⁶
• Some people may have an allergic reaction to the iodine-containing contrast agent used, however, hospitals are equipped to deal with such cases. 
• In rare cases, contrast material containing iodine may cause further kidney damage to those at risk for kidney failure.⁸ Blood tests may be conducted to assess kidney function before CTA to minimise complications.

Summary

Computed tomography angiography (CTA) is a medical imaging technique merging the principles of computed tomography (CT) with angiography to visualise blood vessels. CTA involves administering a contrast material and using a CT scanner to generate 3D images that can help diagnose vascular and cardiovascular diseases alongside blood vessel abnormalities. It is a precise, fast, painless and non-invasive technique that can sometimes diminish the need for surgery or allow surgery to be performed more accurately to minimise complications and maximise patient outcomes.