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Cardiac CT Scan
By Dr. Michael Shapiro
A Painless Procedure Paints a Vivid Picture of the Heart
Cardiac CT scan is the newest type of imaging used to detect heart disease. It allows us to take pictures of the coronary arteries in a non-invasive fashion. Cardiac CT has been around for about ten years, but in the last four years, it’s advanced to the point that it’s now being used in clinical routine.
Typically, when we need to see someone’s coronary arteries in order to detect any possible blockages, the patient has to undergo an invasive coronary angiogram. This is a procedure where a catheter is placed in a patient’s artery in the leg, and then ultimately that catheter is inserted into the coronary arteries.
Cardiac CT is a form of non-invasive coronary angiography. It uses a traditional CT scanner, but with a very high resolution. We can also gate it to the patient’s electrocardiogram (ECG) so that we get virtually motion-free images of the coronary arteries. Cardiac CT only involves placement of an intravenous catheter in one of the arm veins as opposed to inserting a catheter in the heart and coronary arteries. It’s a much more pleasant experience for the patient and with far fewer risks.
The Gate Keeper for the Cath Lab
Currently, we recommend cardiac CT for symptomatic (chest pain) with low to intermediate risk profiles. If the CT scan shows no problems, then we can avoid sending them for a coronary angiogram and they can the risks associated with an invasive procedure. This is an important advantage because approximately 30% of patients who go to the cath lab do not have any significant disease in their coronary arteries and really do need that procedure.
Comparing Risk Factors
The risks associated with invasive coronary angiography are rare (1 in 1000) but serious. They include heart attack, stroke, or bleeding where the catheter is inserted. There is also risk for an allergic reaction to the dye, but this, too, is rare. A reaction can be as small as breaking out in hives to something more serious, such as having trouble breathing to the point that we need to take emergency action.
CT scan does not carry the risks of heart attack, stroke, or bleeding, but the risk of dye allergy is the same.
X-Ray Dose is a Hot Topic
There is a lot of misunderstanding regarding the amount of radiation exposure associated with cardiac CT. Over the last year, newer protocols allow cardiac CTs to be performed at much lower radiation doses that are quite acceptable.
Listed are a few examples of imaging studies involving radiation exposure, compared in millisieverts (mSv) (a unit used to measure the biologic effects of radiation):
|
Chest x-ray
|
|
0.04 mSv
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Nuclear stress test
(depending on the dye used)
|
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15-25 mSv
|
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Life in the U.S.
|
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3 mSv
|
Coronary CT scan
(using traditional protocols)
|
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8-13 mSv
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Cardiac CT scan
(using newer protocols)
|
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3-5 mSv
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Invasive coronary angiogram
(just the pictures without
the angioplasty)
|
|
3-5 mSv
|
You can see that the newer protocols for coronary CT scan have the same radiation exposure as an invasive coronary angiogram, and companies that make the scanners are working to reduce exposure even further.
OHSU –Taking Cardiac CT Scan to the Next Level
Here at Oregon Health and Science University, we have the most advanced technology with our state-of-the-art 256-slice cardiac CT scanner. To give you an idea of how far the scanner has come in a very short time, ten years ago there were just single slice CT scanners. They progressed to 4-slice, then to 16-slice, then to 64-slice before recently making a huge leap to a 256-slice scanner. This scanner allows us to take pictures of the entire heart and coronary arteries in about two seconds. Patients do not need to hold their breath for very long (about five seconds) and most people find the procedure to be very easy. The amazing spatial resolution gives us the ability to see very small structures quite clearly.
To further enhance the experience, we perform the cardiac CTs in our Ambient Room, where patients can listen to music and watch scenes of their choice that are projected onto the ceiling and wall. We’ve been told that the only thing missing is the popcorn.
A future screening tool?
Heart disease is the number one killer in the United States and the Western world. Yet we have no screening device for this deadly disease. I am optimistic that within five to ten years, as radiation exposure lessens even more, Cardiac CT scanning will be widely used to detect heart disease long before symptoms appear – helping us to save many more lives.
Dr. Michael Shapiro is the Director of Cardiac MRI and CT, a cardiothoracic surgeon, and an Assistant Professor at Oregon Health & Science University. He earned his medical degree at the University of Medicine and Dentistry of New Jersey and did his residency at Beth Israel Medical Center in New York City. Dr. Shapiro completed fellowships in Cardiology at Beth Israel Medical Center and in Cardiovascular Imaging at Massachusetts General Hosital, Harvard Medical School.
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