A Snapshot in Time

A full-body scan has benefits and limitations while providing a virtual look inside the body.

by Jon Nalick

In the fictional world of "Star Trek," physicians ascertain their patients' condition simply by having them recline on a table for a medical scan whose results are instantaneous and 100 percent accurate.


Although real world medicine cannot match that kind of accuracy or sophistication yet, it can deliver a rough approximation of a procedure that not long ago existed solely in the realm of science fiction.


Called computed tomography or CT scanning, the procedure uses multiple X-rays to provide a virtual look inside the body, allowing physicians to better assess disease risk and, in some cases, find evidence of disease that might otherwise have gone undetected.


Johnson Lightfoote, M.D., associate professor of clinical radiology and medical director of radiology at USC University Hospital, says that CT imaging is particularly useful because it provides high-resolution images of soft tissue, blood vessels, lungs and bones.


"CT scanning does not replace tests such as mammograms, Pap smears, prostate-specific antigen screening or colonoscopy, but it is useful for identifying coronary artery calcification that can signify hidden disease, as well as osteoporosis, and tumors in the lungs, liver, colon and other organs," Lightfoote says.


The full-body CT scan may detect changes in organs that often appear before anatomical changes or noticeable symptoms, as well as tumors or other abnormalities. The scan is used preventively, to detect disease in its earliest and most treatable stage, and diagnostically, to help determine the course of therapy for those already being treated, he says.


Jeffry Huffman, M.D., professor of urology and CEO of USC Care Medical Group, says he knows firsthand the potential value of CT scanning, having operated on a 55-year-old man whose scan revealed a small but malignant tumor growing on his kidney.


"The scan allowed us to diagnose and treat this problem earlier than would have been possible otherwise-and the earlier you find them, the better," Huffman says. "It is impossible to say whether the scan helped save his life, but it probably allowed us to intervene months before signs of the disease would have appeared."


At the Executive Health and Imaging Center in downtown Los Angeles, USC offers several CT procedures: lung cancer screening, coronary artery calcification screening, colonography and whole- body scans.


A CT scanner is a large machine with a hole through its center. During a scan, patients lie on their backs on a table that slides into the opening as a rotating X-ray device takes multiple images from various angles. A computer then uses the images to create a composite representation of the area scanned.


The procedure is painless and usually takes only a few minutes. Depending on the type of scan being performed, patients may receive contrast dyes-by mouth, injection or enema-to enhance the images.


According to the Food and Drug Administration, the amount of radiation received during a CT scan is about the same as the amount of natural background radiation a person would receive in eight months to three years, depending on the size of the area scanned. Compared to the dosage of radiation a person receives from a standard X-ray, which is small, a person receives about 100 times as much from a head CT scan and 500 times as much from a CT scan of the abdomen.


Lightfoote says that level equates to an additional instance of cancer for one out of 1 million people undergoing the procedure -and that for people under 40, the slight risk probably does not
outweigh the potential benefit. Generally, patients undergoing CT scans are age 40 or older and have a personal history, such as smoking or industrial exposure, or a family history that puts them at higher risk for heart disease or cancer.


A CT scan's strength is in helping determine who is at the highest and lowest risk for cardiovascular and lung diseases. Even so, a clear scan does not necessarily mean a patient is disease-free-and a scan that contains an abnormality does not necessarily demonstrate the presence of disease. Lightfoote stresses that because of that, patients should always have their scans interpreted by a board-certified and experienced radiologist.


"Ideally, for full-body scans, the person who reads the results is a radiologist who is a specialist in the chest and liver. Reading scans takes experience, and the more you read, the better you are," he says.


Despite its potential, CT scanning is not yet a mature field, and "false positives"-results that suggest the presence of disease where none actually exists-remain common.


Edward Grant, M.D., chair of radiology at the Keck School of Medicine, says that as physicians gain experience with CT scanning, the incidence of false positives should decline, and results that
previously would have been considered ambiguous should become reliable data physicians can act on.


"We make judgment calls on angiograms and colonoscopies over which abnormalities need to be biopsied and which don't all the time. And over time, with CT, we're going to improve our ability to make the same kinds of judgments," he says.


Advances in technology are making those kinds of discriminations easier. Lightfoote says that electron-beam CT, one of the first machines available, traded off resolution for speed to solve the
problem of capturing images of a beating heart. Now, more advanced CT scanners, such as the one used by the Executive Health and Imaging Center, offer unprecedented speed and high resolution-scans from the shoulder to pelvis now can take just a few
seconds, he says.


Grant says that the growing popularity of such scanning is a direct result of people wanting to be more involved in their own health care. Still, he warns patients not to ignore yearly check-ups and other regular health screening on the basis of a clear scan because a scan is merely a snapshot in time and not proof that the patient will remain disease-free.


John Brodhead, M.D., associate professor of internal medicine, says that when body scanning first became available, many providers failed to counsel clients appropriately about the results.


"Initially, a lot of them were free-standing radiology centers where a person would simply get a report from the radiologist that said, 'nodule seen in the lung,' but with no discussion about what it
was likely to be. That tended to freak a lot of people out. I had several patients who got scans without talking with me and I received panicked phone calls because the report mentioned that a nodule 'could not be ruled out as cancer,'" Brodhead says.


"Most people hope they get a report that says their internal scan is perfect, but the radiologist is likely to describe every abnormality, even if it is not clinically significant. That's why it is crucial for people to understand before they have the scan that an abnormal result is not indicative of a health-care crisis," he says.


Brodhead notes that many common abnormalities can be easily explained if a physician knows the patient's medical history and adds, "I won't even look at a scan and interpret it without
knowledge of a patient's background and history. Interpreting scans that way really does a disservice because something that looks bad on a scan-but is actually harmless and could have been adequately explained by the patient's history-can prompt an invasive procedure that carries its own risks."


So long as patients understand the limitations as well as the benefits of body scans, Brodhead says he believes they can be a strong asset in providing an overall picture of a person's well-being: "In that context, the scan is additional information that allows both physician and patient to make prudent decisions on health care."