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PET scans

Seeing into the body's metabolic processes

Seeing into the body's metabolic processes

May 28, 2002|By KEVIN CLAPP

The fourth in a monthly series exploring the diagnostic options open to local patients. Last month: Computerized tomography (CT).

Imagine the opportunity to nip colorectal cancer in the bud by detecting tumors earlier than ever before.

Picture the value of stifling a recurrence of breast cancer before tumors have a chance to ravage the body.

All thanks to a medical road show housed in, of all things, a tractor trailer. Think of it as science in a box - a very big box, to be sure, but the prize inside is well worth the wait.

Because this PET has the ability, if not yet the cost efficiency, to be best friend to man, woman and child.

"Not only does it diagnose the cancer, but you can evaluate the treatment," says K. George Sachariah, M.D., P.A., director of nuclear medicine at Washington County Hospital. "You aren't wasting money and time by giving people medicines that don't work."

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Positron Emission Tomography (PET) - it's a new way to combat cancer, heart disease and, in the future, dementia.

Only, it's not so new. Developed in the early 1970s, PET technology remained research oriented until 2000 when the first clinical applications took place.

Even now, PET use is limited. With a price tag of $3.5 million to install a permanent machine, many hospitals, including Washington County and Frederick (Md.) Memorial rely on mobile units that travel from community to community.

Once a week for the last year, a mobile PET unit parks outside the Diagnostic Imaging Services office at Robinwood Medical Center and scans four or five patients each week. May 20, PET visited Frederick Memorial for the first time.

There is no PET access at Chambersburg, Pa., Hospital or at City Hospital and Jefferson Memorial Hospital in West Virginia. City Hospital, in Martinsburg, W.Va., is exploring the mobile PET option.

Jefferson Memorial has no immediate plans to offer PET scan facilities and Chambersburg is waiting to see if there is a market for the diagnostic service.

Resembling a computerized tomography (CT) scanner in shape - a square donut with a hole in the middle and a table that passes through the center - PET takes up to an hour for a full body scan, compared to minutes with CT.

But PET works differently from a CT in that it reveals what's happening within the body's organs.

Tumors crave glucose, suck it up fast as they can. So a sugar solution charged with positrons (the opposite of electrons) is injected through an IV and is given an hour to make its way through the body.

Patients remain at rest prior to the scan. Moving around sends glucose to muscles instead of tumors and would mute the scan.

Positrons interact with electrons in the body; they annihilate each other, creating a radioactive reaction that sends signals flying in opposite directions to be read by the PET's spiral scanner.

The resulting three-dimensional images open a window to the body on a metabolic level for physicians.

"Tumors use a lot more glucose than normal tissue, so the slices of the body that are obtained show us where the glucose is located," says Duke University professor of radiology R. Edward Coleman, M.D.

"It can detect tumors very sensitively when they are small and are generally undetectable by other techniques."

Barry McGowan, nuclear medicine manager at Washington County Hospital, recalls one patient with melanoma on one part of his body who had several scans - CTs, MRIs - that detected nothing further.

A PET revealed spots in the lungs and leg that may otherwise have gone long unnoticed.

On a sample PET scan, Sachariah points to a series of dark masses. The heart and bladder are naturally dark because the organs take care of distribution and flushing of the solution.

Dark, uncommon splotches in the lung and neck, he says, are cancerous.

Sachariah talks at length about the uses for PET that could make other tests and scans unnecessary in some cases. Why perform X, for instance, when Y works 10 times better.

Coleman is excited about the new frontiers for PET scans. Four, five years ago, a whole body scan could last two hours; today it has been cut in at least half.

And as technology improves, so will the test. Within five years, Coleman estimates all PETs sold will be a combination PET and CT scanner. About a third of those sold are already combined, and he says the advantages of having two scans from one machine are vast.

"With PET it's like looking at a weather map, but it's very difficult to know where you are. But you put it on a geographic map and you know where you are," Coleman says. "CT provides anatomic information, provides the map, whereas the PET scanner provides the information about what's going on in the area."

So if there is a scan of the abdomen with PET alone, determining whether a glucose saturated mass is a tumor or an organ that naturally attracts glucose is made easier by using the PET in consort with a CT.

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