Today, to a non-medical person, the array of tests available in a modern hospital’s X-ray or Radiology Department may seem bewildering, the technology intimidating, and the results and possible outcomes (is it cancer? a stroke? a “slipped disc�) often terrifying. The ability to peer inside the body is nothing short of miraculous and has saved countless lives, since Wilhelm Roentgen discovered x-rays in 1895. Six years later, he was honored with the first Nobel Prize in Physics and the collaboration between physicians and physicists had continued ever since, resulting in amazing advances far beyond Roentgen’s wildest dream.
Apart from x-rays and nuclear imaging, the use of more modern imaging techniques, such as CT or computed tomography scan, MRI or magnetic resonance imaging, and PET or positron emission tomography scan, has produced increasing concern among experts, not only because of the huge and growing expense, but even more, because of the potential risk posed by the cumulative exposure to radiation. They are used to diagnose disease, trauma, and abnormalities, as well as to guide and monitor treatment.
Because they’re so commonly used today, CT scans are the biggest source of radiation of all imaging technologies. A special type of x-ray that produces cross-sectional images, or “slices†of the body, CT scans are used to diagnose everything, from heart disease and cancer to brain tumors, kidney stones, and injuries. Abdominal CT scans tend to produce the most radiation — averaging about 500 times more radiation than a simple chest x-ray, and 1,000 times more than a dental x-ray or bone mineral density test (DEXA) used to diagnose osteoporosis (see table). Other types of imaging that use radiation include nuclear diagnostic tests, such as PET scans, as well as fluoroscopy. MRIs and ultrasound, in contrast, do not use radiation.
The major worry is cancer
The major worry is cancer. Ionizing radiation damages the DNA of every cell it strikes. Most cells can repair mild damage on their own, but if the insult is more severe, some cells may escape from the normal mechanisms that control cell division and growth. Whether the damage occurs from one large dose of radiation or many small doses, the consequence can be unrestrained cell multiplication — cancer.
It is not a common occurrence, and it shouldn’t scare us away from reaping the enormous benefits of diagnostic imaging. But it should remind patients and doctors alike to use these wonderful techniques with respect and care.
Doctors have learned to minimize the side effects of ordinary x-rays, but in the 21st century, the large amount of radiation used by CT scans is prompting a reevaluation of the risks and benefits of diagnostic imaging.
Let’s take a look at some imaging techniques that rely on ionizing radiation.
X-rays
Even in this era of CTs and MRIs, ordinary x-rays remain an important tool for diagnosing medical problems ranging from fractures to pneumonia. New digital techniques that use less radiation have made x-rays clearer and safer than ever.
Digital technology though can’t overcome the intrinsic limitations of x-rays: They can’t produce images of tissues that are not dense. Healthy lungs, for example, appear uniformly black because they are filled with air. By using radio dense opaque materials, doctors can obtain images of tissues that otherwise allow x-rays to pass right through — such as in angiography for blood vessels, barium enema for the colon, and intravenous pyelography (IVP) for the kidneys, ureters and bladder. Although these techniques have improved diagnosis and therapy, they deliver more ionizing radiation than plain x-rays.
CT scans
Computed tomography (CT) scanning, sometimes called computer-assisted tomography or CAT scanning, appeared on the scene in the early 1970s, altering the imaging landscape forever. CTs also use x-rays to image the body. New modern techniques though are making CTs better than ever, but they often deliver larger amounts of radiation as they produce images of superior quality. For example, the new generation multislice scanners are remarkably fast, able to scan a patient’s entire chest, abdomen, and pelvis, while he holds his breath for just a few seconds. By focusing on a slightly smaller area of the body, doctors can use the same few seconds to obtain much finer slices that provide remarkably detailed images of the body in 1-millimeter segments.
The use of these new imaging techniques has increased dramatically in medical practice. In the US, for instance, about 80 million scans are performed annually and the number is increasing by about 10 percent per year. In all, CTs now account for approximately two-thirds of medical radiation in the United States! It is estimated that at least one-third of all these scans may be unnecessary. The hard part is to define “unnecessary†and minimize the risks posed by appropriate testing.
Reducing risk
While there’s debate about such estimates and the magnitude of risk from medical imaging, everyone agrees that unnecessary radiation exposure should be eliminated. But why are doctors doing so many imaging tests?
• Doctors may order tests out of habit, wanting to “leave no stone unturned,†and may not focus on radiation doses or the cancer risks of medical imaging. They may also order scans because of fear of failing to diagnose something and being sued for malpractice.
• Patients may pressure doctors for scans, feeling that high-tech testing is optimal care, or “just to be safe.†They may be influenced by ads that promote the benefits of diagnostic imaging but underplay the risks and costs.
• There’s an increased supply of machines, and doctors who own them or have a financial stake in the facilities have an incentive to order more scans.
• As scanning machines become faster and more powerful, providing greater resolution (and often more radiation), more “incidental findings†are detected. These findings are often clinically insignificant, but lead to more testing and possibly overtreatment.
• Certain conditions, such as cancer and some cardiac problems, may need periodic monitoring.
• CT scans are also being used more often for screening healthy people, without evidence of benefit. Some examples: CT scans of smokers and former smokers for lung cancer; and “full-body†scans that are promoted as a way to detect a variety of cancers, cardiovascular disease, and other disorders.
What to do
The Department of Health and the Philippine College of Radiology advise that imaging tests be done only if there is a clear benefit that outweighs the risks — and that the minimal level of radiation be used. Among the questions you should ask before doing a diagnostic scan are:
√ Is this test really necessary, and will it improve my health care?
√ Is there a nonradiation alternative, such as ultrasound or MRI, that’s equally good? Keep in mind, though, that CT is better for certain things (such as broken bones, damaged vertebrae, cancer, pneumonia, bleeding in the brain, organ injuries), while MRIs are better for others (tendons, ligaments, spinal cord, brain tumors, most strokes); sometimes both are used. MRIs are more expensive.
√ Is the facility accredited by the Department of Health and is the medical staff certified by the Philippine Board of Radiology?
√ Will the test use the lowest amount of radiation and fewest scans for adequate imaging? For children, it’s important to make sure the radiation level is appropriate for their smaller size.
√ Will the scan be limited to the indicated area, and will nearby areas be properly shielded?
Scanner for security
In our frightening new world, x-rays and CTs have become as important for airports as for hospitals. Hand luggage is put through x-ray scanners; because one pass exposes your items to only a tiny fraction of the energy used in a chest x-ray, these scanners are safe for photographic film — and for the security personnel who use them all day long. But checked baggage is passed through CT scanners that are far more powerful; they will damage your film but not your medications.
The new full-body scanners have raised concerns about privacy and safety. The privacy issue is personal, but the safety issue is a scientific matter — and scientists agree that scanners are safe. Two types are in use. Millimeter wave scanners use radio waves to generate images, and they don’t expose travelers to any ionizing radiation. Backscatter scanners do use low-intensity x-rays, but they bounce off the skin without penetrating the body. They deliver only a tiny amount of radiation, about the same amount as you get in three to nine minutes of daily living, or about 1/1000 as much as an ordinary chest x-ray. A person would need to have 2,500 to 5,000 backscatter scans a year to reach the established annual safety limit.
Bottom line
Medical imaging tests are invaluable in the diagnosis and treatment of many disorders. You shouldn’t avoid necessary exams and procedures out of concern about radiation. And if the test doesn’t find anything, that doesn’t mean it was unnecessary. But unless your doctor suggests it, don’t go to those widely advertised clinics offering full-body or coronary screening CT scans (some are even part of medical tourism trips in a few Southeast Asian countries) for the “worried well.†The best advice: Before having any imaging scan, discuss the pros and cons with your doctor.