CTA vs. MRA vs. Angiography

For my blog this week I decided to learn more about how physicians order neck imaging exams for signs and symptoms of vessel stenosis or occlusion. When do they order CTA, MRA, vascular ultrasound, or conventional angiography? I wanted to learn more about this topic because I didn’t know which modalities are considered better or when they are used. So here is what I learned. In general, conventional angiography is now used mainly for treatment and CTA, MRA and ultrasound are used for diagnosis. This is a shift from the past when conventional angiography was used for both diagnosis and treatment. In the absence of specific symptoms these tests are usually ordered after some type of abnormality is shown in a CT or MR scan. The tests will be ordered directly if the patient comes into the emergency room showing symptoms of occlusion. CTA, MRA and ultrasound are used for diagnosis because they are less invasive and do not involve a femoral stick and catheter placement, thus they are less risky for the patient. In addition, they can be done by a technologist rather than a physician.

I did some reading on the web about vascular ultrasound and discovered that this is a good initial screening test. Advantages are it is non-invasive, inexpensive and can be done at the bedside. Disadvantages are it is better for surface vessels but less accurate for deeper vessels. It is also fairly operator dependent so the technologist needs to be highly skilled in order to get an accurate result. If abnormal results are noted then a CTA or MRA is usually ordered. The CTA or MRA can usually give enough information so that surgery decisions can be made although some physicians like to have both a CTA and MRA done before surgery.

So when should a CTA vs. a MRA be ordered? Obviously, any patient who is allergic to iodinated contrast should have an MRA. A patient with a lot of metal in their body should be scheduled for a CTA. A patient with severely impaired renal function could have a MRA with 2D time of flight images (no contrast needed). In general, the cardiology community prefers MRA for evaluation of the carotids and CTA for evaluation of the aorta (although I found another study which indicates MRA is now preferred for the aorta). MRA is better for showing perfusion and function. CTA would be better if there was also suspected lung or airway involvement (i.e. pulmonary embolism in conjunction with stroke). For critically ill patients CTA would be faster than MRA. If a patient required repeat studies over time then MRA would be preferred (less radiation dose). CTA tends to be better in showing the coronary arteries in young children.

I thought this was a worthwhile blog for the week. Now I feel I could answer a patient question if I were asked why a CTA had been ordered vs. another type of imaging study. The image above is of an MRA of the neck.

References and Image:

Gallo, B (2008). Magnetic Resonance Angiography (MRA) and Computed Tomography Angiography (CTA): The new gold standards in vascular imaging. http://www.frost.com/prod/servlet/market-insight-top.pag?docid=144155345

http://www.tramedicalimaging.com/assets/news/TRA_News_12_03.pdf

http://radiologycme.stanford.edu/2008mdct/handouts/tue/1505-Chan-MRA_CTA.pdf

http://www.anthem.com/medicalpolicies/guidelines/gl_pw_a053801.htm

http://www.sikermedical.com/services/mri/mra_carotids/

http://www.imaginggroupde.com/images/mr_angiography_neck.jpg

All studies accessed via web on November 17, 2009