It's What's Inside That Counts with X-rays, Other Imaging Methods
by Tamar Nordenberg
Within a year of German scientist Wilhelm Roentgen's discovery of x-rays in 1895, people throughout the world knew about Roentgen's work and had seen his first x-ray picture--his wife Bertha's hand, showing her bones, wedding ring, and all. Even before Roentgen was awarded the first Nobel Prize in physics in 1901 for his discovery, x-ray studios were popping up that sold bone portraits for display in the home.
As their popularity grew, some publications contained inflated claims about x-rays--they could restore vision to the blind, they could raise the dead. Other people expressed a far more skeptical view: "I can see no future in the field," the head of one x-ray clinic reportedly proclaimed. "All the bones of the body and foreign bodies have been demonstrated."
But x-ray was far from a dead-end technology. Instead, it marked the start of a revolution in medical diagnosis. Like other medical imaging technologies that followed, including ultrasound, computed tomography (or CT) scanning, and magnetic resonance imaging (or MRI), x-ray can help doctors narrow down the causes of a patient's symptoms without surgery and sometimes diagnose an illness before symptoms even appear. While it can't help a blind person see again, used appropriately, medical imaging can be a useful first step in treating a range of problems, from a simple broken bone to a cancerous tumor.
Using medical imaging appropriately, explains William Sacks, M.D., a medical officer in the Food and Drug Administration's radiology branch, means always considering the risks from a device along with its benefits. X-rays and some other imaging tests use radiation, after all, which can have serious health consequences if used improperly. FDA looks at both the risk and benefit sides of the equation to decide whether to allow marketing of a device, Sacks says. And doctors judge the risks versus the benefits in deciding if a test is medically necessary.
FDA, the U.S. Environmental Protection Agency, and other federal and state agencies share the responsibility for protecting the public from unnecessary radiation. For its part, FDA regulates x-ray equipment and all other electronic radiation-emitting products (including nonmedical consumer products, such as microwave ovens) under the Radiation Control for Health and Safety Act. For all electronic imaging devices, the agency develops and enforces standards to ensure that only safe and effective devices are allowed to be marketed.
"Nothing is entirely safe, of course, including walking down the sidewalk," Sacks says. "The question to ask is, 'In balance, do the benefits of x-ray outweigh the safety concerns?' The benefit of making bone portraits for display, like they did at the beginning of the century, is near zero. Now that we know the health risks from certain doses of radiation, we don't order x-rays willy-nilly, but only if there is a health reason to find out something imaging is capable of telling us."
Black-and-White Photo
Roentgen labeled the rays he discovered with the scientific symbol "X," meaning unknown, because he didn't understand their makeup at first. x-rays are actually electromagnetic waves. When they are passed through a patient's body to a photographic film on the other side, they create a picture of internal body structures called a radiograph.
Chest radiographs, which are among the most common imaging tests, can reveal abnormalities of the lungs (such as pneumonia, tumor or fluid), heart (such as congestive heart failure or enlarged heart), and rib cage (such as broken or abnormal bones).
Other common types of x-ray examinations include dental studies to detect cavities and other tooth and gum problems; abdominal studies, which can reveal abnormalities of not just the abdomen, but also the liver, spleen, gallbladder, and kidneys; gastrointestinal studies of the upper or lower GI tract; studies of the joints to assess things like arthritis and sports injuries; and mammograms, which can help detect breast cancer with the use of special x-ray equipment. (See "FDA Sets Higher Standards for Mammography" in this issue of FDA Consumer.)
Getting a radiograph takes only a few minutes, at a doctor's office or a radiology unit of a hospital or separate location. After positioning the patient with the body part to be examined between the unit that emits the rays and an x-ray film cassette, the doctor or technician steps away from the area and presses a button or otherwise activates the x-ray machine to take the picture.
The less dense a structure of the body is, the more radiation passes through it and reaches the film. The x-rays expose the film, changing its color after it is developed to gray or black, much like light would darken photographic film.
Bones, as well as tumors, are more dense than soft tissues. They appear white or light on the x-ray film because they absorb much of the radiation, leaving the film only slightly exposed. Structures that are less solid than bone, such as skin, fat, muscles, blood vessels, and the lungs, intestines, and other organs, appear darker on the film because they let more of the x-rays pass through. Likewise, a break in a bone allows the x-ray beams to pass through, so the break appears as a dark line in the otherwise white bone.
To make certain organs stand out more clearly, a "contrast medium"--a substance that blocks x-rays rather than transmitting any--can be introduced into the body, in the form of a drink or injection. Barium sulfate is commonly used to study the gastrointestinal tract, while iodine-containing dyes are often used to provide information about the gallbladder, kidneys, blood vessels (using a technique called angiography), or the cavities of the heart.
FDA regulates these contrast agent drugs to make sure they are safe for patients and helpful in diagnosing their medical condition.
Reasonable Risk
Because x-rays are a type of radiation, patients sometimes express concerns that the test may harm them somehow, perhaps increase their risk of cancer. It's true that overexposure to x-rays can damage or destroy living tissue, potentially causing skin burns and even cancer. But for typical diagnostic x-rays, patient exposure is "minimal," Sacks says.
Experts estimate that a person in the United States gets only 20 percent of their radiation exposure, on average, from medical x-rays and other man-made sources. The remaining 80 percent comes from natural--and usually unavoidable--sources, such as radon gas, the human body, outer space, and rocks and soil.
Many factors affect a person's actual dose of radiation each year. One of the most influential factors is the elevation of a person's home town. The higher the elevation, the thinner the atmosphere and the greater one's exposure to cosmic radiation from outer space. At sea level, FDA's Sacks explains, a person typically gets about two chest x-rays' worth of cosmic radiation each year. That amount can be significantly higher, he says, in high-altitude cities like Denver or Santa Fe.
Particularly over the last two decades, improvements in x-ray technology have meant decreasing patient exposure to radiation. Not as high a dose of radiation is needed to get a useful diagnostic image, and the rays can be focused more precisely on the part of the body to be studied.
Still, some precautions are taken to make the x-ray procedure even safer. For example, a lead apron sometimes is placed over those parts of the body not being studied, especially the reproductive organs, which are extrasensitive to radiation. Because radiation exposure can cause birth defects to a fetus in certain stages of development, pregnant women should get x-rays only when absolutely needed, and a lead apron should be used to shield the mother and fetus when possible.
Beyond the Conventional
Unlike conventional x-rays, which take a single picture of a part of the body, an updated version of the technology called computed tomography generates hundreds of x-ray images in a single examination. Despite the large number of images, the total amount of radiation can be less from a 30- to 45-minute CT scan than from some conventional x-ray procedures.
The patient lies still on an examination table that slides into a circular opening in the CT scanner. The x-ray tube that surrounds the patient takes the pictures from many different directions, and then a computer takes the images and constructs them into two-dimensional cross sections of the body, which can be viewed on a television screen.
"There was nothing uncomfortable about the test, nothing to be afraid of," says Wanda Diak, the managing director of a support network called CancerHope, who underwent several CT scans in 1996 and '97 to track the status of her ovarian cancer.
Computed tomography produces detailed images that can sometimes reveal abnormalities an ordinary x-ray would not pick up. CT scanning can be useful in checking the brain for tumors, aneurysms, bleeding, or other abnormalities. Also, it can unveil tumors, cysts, or other problems in the liver, spleen, pancreas, lungs, kidneys, pelvis, lymph glands, and other body parts.
It was a CT scan that first revealed an abnormality last September in the colon of Yankees outfielder Darryl Strawberry. Because of the baseball player's prolonged stomach cramps and other symptoms, doctors performed the CT scan and followed up with a procedure called colonoscopy. Based on the tests, doctors reportedly removed a tumor and part of Strawberry's large intestine. Strawberry will undergo six months of chemotherapy, also.
Doctors have expressed optimism about a full recovery for the athlete. Strawberry himself told his fans at an appearance last October, "My chances are great. Don't worry, I'm gonna live."
Powerful Magnet
First cleared for marketing in 1984, magnetic resonance imaging, like x-ray and CT scanning, provides a look inside the body without surgery. MRI differs in a basic respect from its predecessor technologies, however: MRI uses a strong magnetic field, not x-rays, to create a picture of the internal body structure being studied.
Typically, during MRI, the patient lies on a table that slides into a tubular scanner for the 30- to 90-minute test. Patients are often given earphones to wear while inside the tunnel to block out the loud clanking noises the machine makes.
Inside the tube, a large, donut-shaped magnet creates a magnetic field. Pulse radio waves are directed into the magnetic field and absorbed by hydrogen atoms in the body. The machine's computers create an image of the body's internal structure by measuring the emission of energy from the movement of hydrogen atoms within the patient's body.
MRI is especially useful in studying the brain and spinal cord, the soft tissues of the body, and the joints. Because this technique shows distinct contrast between normal and abnormal tissues, it is sometimes superior to CT scanning and other imaging methods in evaluating tumors, tissue damage, and blood flow.
MRI scanning has no known long-term risks. No jewelry or other metal can be carried or worn during the exam, though, because of the very strong magnetic field. Most importantly, the health professional overseeing the treatment must be told if a patient has a pacemaker, hearing aid, any metal implants such as artificial joints, plates, or screws, or other metal implants or electrical devices. The magnet could interfere with these devices and cause serious injury, even death in the case of a pacemaker.
While MRI is a painless procedure, people who tend to feel claustrophobic may be uncomfortable inside the tunnel. For those people, anti-anxiety medicines are available, or they may choose a hospital or clinic that offers the less confining "open MRI" machine.
Sound Study
Ultrasound scanning isn't just for viewing a developing fetus, anymore. Originally used for this purpose, ultrasound today substitutes for conventional x-rays in the diagnosis of many conditions, commonly those involving the kidneys, bladder and uterus, the heart (called echocardiography), and the spleen, gallbladder and pancreas. However, ultrasound does not produce clear images of the lungs and other organs filled with gas or air.
With an ultrasound exam, a gel is spread over the skin covering the area of interest, and a "transducer" is moved back and forth to gather data. The transducer sends out high-frequency sound waves, far above the range of human hearing. When the waves hit the body part being studied, some are absorbed by tissues, and some are echoed back to a transducer. The machine measures the amount of sound reflected back, and displays an image called a sonogram on a monitor or on videotape or graph paper.
An ultrasound exam can take anywhere from 15 minutes to an hour.
While ultrasound is considered risk-free, FDA's Sacks says it still should be used only when medically warranted because "[t]here's no point in taking a chance for anything but a medical reason."
Helicopter or Zamboni
So, which diagnostic imaging technique is best? "Best for what? It really depends what you're looking for," says board-certified diagnostic radiologist Mark E. Klein, M.D. He likens the question to asking which mode of transportation is best: "In the mountains, you'd want a helicopter or four-wheel drive. On ice, you'd want a Zamboni." For example, he says, a skull x-ray to look for a brain lesion is useless, so the best choice might be a CT scan or MRI. For a broken arm, an x-ray would do the job and is preferred over an MRI.
X-ray, CT scanning, MRI, and ultrasound are among the most common noninvasive procedures (or minimally invasive, in some cases when a contrast agent is used), but the diagnostic options don't end there. Nuclear scanning, including two techniques called positron emission tomography (PET) and single photon emission computed tomography (SPECT), use radioactive substances introduced into the body to discern abnormal from normal body structures or evaluate the body's functioning. Other, sometimes riskier procedures require the insertion of tubes or instruments into the body.
A patient should know why the doctor is choosing a certain imaging technique, Sacks says. "The patient ought to feel secure about what's being done and understand the doctor's reasoning: 'What information does the doctor expect to get from this test?'"
During the test, too, the technician or radiologist can help the patient feel more secure. Julie (who asked that her last name not be used) says she didn't feel upset or panicky during her MRIs in 1997 to follow her uterine cancer. "The technicians were very careful to help me understand what to expect and what I would feel--10 seconds of this, a minute of that, hold still for this length of time. I felt thoroughly prepared for it."
Her last MRI confirmed that she was "all clean" of cancer. "Even if the tests revealed bad news, I'm very thrilled they were there to give doctors a good view of my situation."
Wanda Diak's ovarian cancer has not been evident for almost three years. During her follow-up exams, she says, her doctor sometimes taps on her stomach to check for signs of recurrence. The method seemed primitive to Diak, but her doctor pointed out that before CT scans and other imaging, different sounds were all doctors had to clue them in to an abnormality.
"I think about someone tapping on your stomach rather than having this image that essentially slices you in half so you can see inside," Diak says. "It's like the caveman to the year 2000."
Tamar Nordenberg is a staff writer for FDA Consumer.
While healthy people try to avoid extra doses of radiation, patients with many different kinds of cancer can turn the cell-destroying property of radiation to their benefit. According to the National Cancer Institute, at least half of cancer patients are treated with radiation therapy (sometimes called "radiotherapy") to cure the cancer or improve the quality of their lives by shrinking tumors and reducing symptoms.
Used alone or in combination with surgery, chemotherapy, or other treatments, radiotherapy aims to kill cancer cells with brief, high doses of radiation. In the most common type of radiation therapy, the external type, a machine directs the high-energy rays at the cancer cells.
Healthy cells that surround the cancer cells can be harmed, too, but the therapy works because cancer cells seem to be damaged more than noncancerous ones.
Side effects from radiation therapy can range from mild to serious, depending mostly on which part of the body is being treated and the dose of radiation used. The most common side effects include loss of appetite, fatigue, and skin changes.
--T.N.
FDA Consumer magazine (January-February 1999)
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