To Scan Or Not To Scan
This month's responses are provided by Dr. Janet Storella, a radiologist who is medical director of GCM-Suburban Imaging in Bethesda. GCM-Suburban Imaging is a collaboration between Suburban Hospital and the well-established radiology practice of Drs. Groover, Christie and Merritt. The Imaging Center is located in the new Suburban Outpatient Medical Center at 6420 Rockledge Drive, Bethesda, Maryland. For more information call Suburban On-Call at (301) 896-3939. To schedule an appointment call (301) 897-5656.
I'm confused about the different imaging technologies. What is the difference between MRI and CT.
CT (computed axial tomography) uses X-rays to see structures inside the body. These X-rays are aimed at a particular area of your body and the ones that pass through your body are received on a detector. A computer then analyzes this data and "builds" a picture of what is inside.
MRI (magnetic resonance imaging) takes advantage of the natural magnetic properties of the tissues in your body. The machine is a strong magnet that sends radio waves through the body. The magnetic tissues in the body then send a faint radio signal back. The receiver collects all those signals and the computer builds a picture of what is inside. MRI is not used for screening, only for diagnostic use.
My friend paid out of her own pocket to have a full body scan. What is this exam? What kind of technology is used?
The exam is full body CT screening. The idea, as in any screening exam, is to find disease before it becomes otherwise apparent in someone who has no symptoms or problems. Diagnostic CT scanning to examine specific parts of the body when there is a problem has been in use for decades. But scanning almost the entire body for screening is a new concept. Other examples of screening exams that most people are familiar with include screening mammography to detect breast tumors before they are felt as lumps or the PSA blood test to detect prostate cancer.
Do you recommend full body scans for people who have no symptoms of disease. What are the pros and cons.
Full body CT screening is controversial. The potential benefit is the early detection of significant diseases, such as tumors. Most of us believe that early detection saves lives -- if we find a tumor while it is still small and has not spread, presumably you can be cured.
The risk is that of radiation exposure. X-rays can cause damage to cells in your body. Even at the low doses used for screening exams there is a theoretical risk of causing cancer and we do not have exact data to estimate that risk. Of course, that risk of radiation exposure should be put into perspective and compared with other risks we take every day and don't even think about. Would you decline to live in Denver because there is a higher background radiation exposure due to the elevation?
There are other potential downsides. An abnormality can be found that is due to a benign or inconsequential process, but leads to additional testing or even a biopsy. The exam also has its limitations - it can't detect every abnormality, and so a normal screening exam doesn't absolutely rule out the possibility of cancer or other significant disease.
With all these issues in mind, and after studying what data we have so far, the two exams that seem least controversial are cardiac calcium scoring to assess the risk of cardiovascular disease and screening CT of the lungs in smokers over the age of 50.
Do I need a doctor's referral? Do I have to pay out of pocket?
Insurance companies do not pay for these screening exams and so up front payment at the time of the exam is expected. Some centers require a doctor's referral and others do not. You would have to check with a specific center.
What is virtual colonoscopy? What are the pros and cons? Is it better than having regular colonoscopy?
Virtual colonoscopy is a CT screening exam to look inside the colon without having to pass a scope into the colon. It still requires a preparation to clean out the bowel and you still need to pump some air into the colon. However, the exam itself is more comfortable than regular colonoscopy and therefore no sedation is required. An advantage of a regular colonoscopy is the ability to perform a biopsy of an abnormal area at the same time, but this also adds an additional risk of perforation (creating a hole in the colon).
Don't these different technologies use radiation and isn't that dangerous?
See above.
What is a PET scan?
PET scanning is a new imaging test that looks at the metabolic activity of tissues. It uses a radio-labelled glucose analog that accumulates in tissues with high metabolic rates. The tissue of many cancers grows rapidly and have a high metabolic rate even if they are small. This is in contrast to CT scanning, which relies on changes in size and shape of tissues to recognize abnormalities. This new PET technology is very promising and has been approved for use in evaluating several tumors including lymphoma, melanoma, lung cancer, and colon cancer.
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