(Page 2 of 3)

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.

Tags: Health

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.