With most chronic illness comes lots of testing. Some radiology tests can seem a little scary—being shoved into a tiny tube or pressing your body awkwardly against a machine. You’re instructed to look away from the light, hold your breath, and stay still. Loud noises, bright flashes, and claustrophobic quarters round out the uncomfortable process. The tests take only minutes, but what about the effects? Could they be long-lasting?
Using the same type of radiant energy as light or radio waves, one beam of electromagnetic radiation emits X-ray particles through the body. Different features—liquid, bone—reflect off the particles and appear white, gray, or black on the X-ray image according to their density. The standards of radiation used for X-rays are consistently reviewed and updated by national and international radiology organizations.
A chest computed tomography (CT) scan is a more detailed X-ray. A CT takes pictures, or “slices”, of the lungs to create a 3-D model of the organ. Think of it as looking at one slice within a loaf of bread. An X-ray uses only one radiation beam, whereas a CT uses several beams. This carves out a more detailed image, exposing hundreds of layers of an organ, including tissue and blood vessels.
A bone density scan, or dual-energy x-ray absorptiometry (DXA) scan, uses radiation to measure bone mineral density to detect bone loss for early signs of osteoporosis and fracture risk. Usually the hip or spine is scanned.
MRI, or magnetic resonance imaging,is a cross-section of internal organs from a multitude of angles—front, side, above. Unlike other diagnostic tests, MRI does not use radiation. Instead, a combination of magnetic forces and radiofrequency waves read the movement of hydrogen atoms in the body. The signals from this reading are then translated into a black and white picture.
X-rays, CTs, and DXA diagnostic scans all subject patients to radiation. High levels of radiation are associated with increased cancer risk. However, the risk of being exposed to radiation from diagnostic testing is relatively unknown. There is no conclusive evidence that these tests will cause any real harm in patients.
Humans are exposed to radiation every day from natural sources in the atmosphere. According to the American College of Radiology, people in the U.S. receive roughly 3 millisievert (mSv) of radiation per year. In contrast, most diagnostic tests have a much lower measurement of radiation, as seen below.
DXA: 0.001 mSv
Chest X-ray: 0.1 mSv
Chest CT (low dose): 1.5 mSv
Chest CT (standard): 7 mSv
Here’s a visual comparison of the radiation in common diagnostic tests to average atmospheric radiation:
To see how other types of diagnostic tests compare, take a look at this radiation chart.
With any radiation exposure, there are risks. “It’s likely, though it’s not been proven, that there is a very small accumulative risk over a lifetime,” explains Dr. Frank Sciurba, associate professor of medicine and education at the University of Pittsburgh School of Medicine and director of the Emphysema/COPD Research Center at UPMC.
Diagnostic tests for COPD
Getting a chest X-ray is crucial for diagnosing COPD, says Sciurba. Your doctor first needs to rule out any other causes for your respiratory symptoms, such as pulmonary fibrosis or bronchiectasis, which can be determined by looking at an X-ray. They may also order a chest X-ray if you’re experiencing significant changes in symptoms.
There are currently no recommendations for physicians to order annual chest X-rays or CTs for COPD patients. However, this could change in the near future. A 2011 study by the National Lung Screening Trial published in the New England Journal of Medicine found annual chest CT scans of former and current heavy smokers helped researchers diagnose lung cancer better. The testing helped reduce the number of lung cancer mortalities in two years by 20 percent. This study shows the potential benefits of yearly CT scans in COPD patients, since majority are current or former smokers.
Sciurba says CT scans are requested for patients with advanced COPD because they show the distribution of emphysema, which gives the doctor an idea if someone is a candidate for surgery, such as lung reduction or bronchoscopic reduction procedures. There are two types of CT scans: low dose and standard. A low-dose CT scan uses a lower amount of radiation compared to a standard scan. Standard CTs are still ordered for cases requiring higher resolution, explains Sciurba; for example, obese patients or finding a pulmonary embolism [blood clot in the lungs]. Low-dose scans detect lung nodules that would indicate early stages of lung cancer.
Since COPD patients run a higher risk of developing osteoporosis, DXA scans are also required. These scans have the least amount of radiation of all diagnostic tests. It is one-tenth the radiation exposure of a chest X-ray and less than the natural radiation exposure people receive in a day. Sciurba says the risks from DXA scans are miniscule compared to the dangers of osteoporosis and painful bone fractures.
The bottom line
Chances are the radiation from diagnostic tests will not harm you, but skipping them could. “The potential consequences of not discovering something are much greater than the low accumulative risk of radiation in an older person from a X-ray or CT scan,” says Sciurba. “The potential consequences are much more immediate, more serious, and not theoretical at all. The benefit, I believe, pretty strongly outweighs the risks.” On the other hand, Sciurba says doctors should not frequently order tests without cause. He advises patients to trust their doctor that if a scan is ordered, there is usually a good reason for it.