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 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 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.
The number of medical tests performed annually in the United States using ionizing radiation more than doubled between 1980 and 2006, according to a study published in Radiology. Almost half of these tests were done on people with cardiovascular disease.
A separate study involving nearly one million people, published in the Journal of the American College of Cardiology in 2010, found that one in 10 adults underwent at least one cardiac imaging procedure with radiation exposure during the three-year study period. The study found that with advancing age came an increasingly higher proportion of radiation dose from imaging procedures.
The tests in question
Tests that employ ionizing radiation include nuclear medicine stress tests, coronary angiography, coronary artery calcium scans (CAC), and coronary computed tomography angiography (CCTA).
• 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 CAC scan is a noninvasive test that uses specialized computed tomography to detect calcium deposits found within plaque in the coronary arteries. The amount of coronary artery calcium is a meaningful predictor of future cardiac events.
• 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.
How much is too much?
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. One recent study found 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.
The heart of the matter
Is there anything you can do to lower your radiation exposure? The American Heart Association recommends “judicious” use of heart scans, so people without chest pain or other symptoms of heart disease may want 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.
In 2014, the American College of Cardiology called for shared decision-making between doctors and patients when radiation is used. Among the recommendations was one stating that if the effective radiation dose of a procedure exceeds 20 millisieverts (or mSv, the scientific unit of measurement for radiation dose), the ordering physician should have a detailed discussion with the patient about radiation exposure risks and any projected cancer risks, or obtain written informed consent from the patient.
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.
• Let your doctor know if you’ve ever had other medical tests that involved radiation.
• 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.