How to reduce the radiation risks of these valuable diagnostic tests
Many types of tests are used to assess a person's heart attack risk or to diagnose coronary heart disease. Some of these tests use ionizing radiation to produce highly detailed images of the heart and its arteries.
These tests, known as cardiac imaging or heart-imaging studies, are valuable and no doubt save lives. At the same time, experts have expressed concerns about the potential cancer risks from the radiation required to perform them.
Read on to learn why ionizing radiation can pose a risk, which cardiac imaging tests expose you to radiation and how much, and what you and your doctor can do to minimize the risks.
What Is Ionizing Radiation?
Ionizing radiation consists of energy waves and particles that are able to travel through the body the way light and radio signals travel through the air. Radiation is present in very low levels in our environment, for example, from soil, rocks, radon, and outer space. Consumer products like TVs and cell phones also emit small amounts of radiation. But most of our exposure comes from medical imaging tests that involve the use of x-rays or radioactive substances.
At very high doses—such as during the atomic bomb blasts of World War II—radiation is known to damage DNA in human cells and cause cancer. Even though the amount of radiation used in medical tests is much smaller and the risk of cancer much lower, no radiation dose has been deemed completely safe.
Rising Radiation Exposure
The number of medical tests performed annually in the United States using ionizing radiation more than doubled between 1980 and 2006, according to a 2009 study in Radiology. Almost half of these tests were done on people with cardiovascular disease.
What's more, the collective annual dosage of radiation from these tests increased by a whopping sevenfold. This means that not only is medical imaging on the rise, so is the dose of radiation used in each test.
Another study, published in Circulation in 2009, looked at the records of 64,074 patients treated for a heart attack at 49 U.S. hospitals between 2006 and 2009. These patients received a total of 276,651 tests that used ionizing radiation during their hospital stay—an average of seven tests per patient.
Tests Using Radiation
Tests that employ ionizing radiation include nuclear medicine stress tests, coronary angiography, coronary calcium scans, and coronary computed tomography (CT) angiography.
A nuclear medicine stress test starts out like a standard stress test in which exercise or medication is used to increase your heart rate. But then a radioactive substance (either thallium-201 or technetium-99m) is injected into a vein and travels to your heart, where it can be detected with a special camera. The amount of the radioactive material that appears in different parts of the heart can show which areas of the heart may not be getting enough blood.
Coronary angiography involves taking x-rays of the heart or blood vessels after injecting a contrast agent into the coronary arteries. The contrast agent is injected through a very small tube inserted into the groin.
A coronary calcium scan is a noninvasive test that uses specialized CT to detect calcium deposits found within plaque in the coronary arteries. The amount of coronary calcium is a meaningful predictor of future cardiac events.
Coronary computed tomography angiography (CCTA) produces high-resolution, three-dimensional pictures of the moving heart and vessels to determine if plaque has built up in the coronary arteries. Before the test, an iodine-containing contrast dye is injected into the patient's arm.
Quantifying the Radiation Dosage
Even though the dose of radiation used during one cardiac imaging study is unlikely to cause problems, there is a cumulative effect each time you undergo any kind of medical test that relies on radiation.
Experts use the term "effective dose" to measure the amount of radiation delivered during a specific test, but it doesn't take into account variations among individual patients, such as age, body weight, or possible sensitivities in the internal organs. Radiation doses can also vary depending on the specific machine used.
In some cases, a different approach to screening can result in higher or lower doses. In a 2009 study from the Archives of Internal Medicine, researchers calculated that the radiation dose from a single CCTA scan varied more than 10-fold depending on the screening protocol that was used.
Fortunately, findings like these are altering the practice of medical imaging. Manufacturers and imaging specialists have responded by developing new technologies and protocols to lower radiation exposure. Newer CT scanners, called "multidetector" or "multislice" scanners, for example, involve less radiation exposure than older ones.
Is There Anything You Can Do to Lower Your Radiation Exposure?
An advisory committee formed in 2009 by the American Heart Association advises people without chest pain or other symptoms of heart disease to think twice about agreeing to heart imaging studies involving radiation. If you have symptoms, however, the benefit of using these tests to come up with a diagnosis and treatment plan outweighs the risks in the vast majority of cases.
If your doctor recommends a heart-imaging test, here are a few strategies to consider:
- Ask your doctor if another kind of test—one that doesn't use radiation—might be just as effective in your situation. Stress echocardiograms, for example, use harmless sound waves to visualize the heart chambers and detect blood clots.
- If you've ever had other medical tests that involved radiation, let your doctor know.
- Ask the radiologist whether a lower dose of radiation can be used.
- Question your physician if he or she recommends a regular heart-imaging study as a preventive measure. These tests should be used sparingly and are not meant for general screening.
Radiation Exposure from Common Medical Tests
Here's a list of the radiation doses from a number of medical imaging tests. To put the numbers in perspective, consider that your annual radiation dosage from natural sources is 2.5 mSv per year.
Medical Procedure and Effective Radiation Dose in Millisieverts (mSv)
Dental x-ray: 0.005
Chest x-ray: 0.02
Coronary calcium scan: 2 (1-1.5 with new technology)
Coronary angiography: 5
Abdominal/pelvic CT scan: 10
Nuclear medicine stress test with technetium-99m: 11
Coronary CT angiography: 12 (5-10 with new technology)
Nuclear medicine stress test with thallium-201: 22