HealthKey: Doctors concerned about supply of nuclear material used in diagnostic tests

  • Johns Hopkins cardiologist Richard George compares images of a heart that were done with the isotopes technesium, left, and thallium, right.
Johns Hopkins cardiologist Richard George compares images… (Barbara Haddock Taylor,…)
August 21, 2010|By Meredith Cohn, The Baltimore Sun

A shortage of imported radioactive material widely used to diagnose heart problems and other maladies has had doctors locally and across the country scrambling for alternatives, including some with higher costs and lower quality.

The nation's supply of technetium has been low for the past 15 months since its main supplier, a Canadian nuclear reactor, went offline. And while production is now ramping back up, the incident has put a spotlight on the country's dependence on foreign sources of the workhorse isotope.

Many in the field are now calling for domestic production and further development of other technology because the aging reactor in Ontario could break down again and is slated to go offline permanently in 2016.

Some consequences of another shortage could be more misdiagnosis of disease and unnecessary procedures.

"There is a parallel to our concern about our dependence on foreign oil," said Dr. Vasken Dilsizian, chief of the nuclear medicine division and director of cardiovascular nuclear medicine and PET imaging at the University of Maryland Medical Center. "Only, in this case the parent isotope has a short half-life, further limiting where we can get it from."

Technetium-99m is made from molybdenum-99, and a third of the world's supply comes from the Chalk River reactor owned by Atomic Energy of Canada Ltd., although the United States also imports some from the Netherlands and other sources. It's now used in the bulk of the nation's 20 million annual nuclear medicine procedures, half of which are cardiac imaging such as "stress tests."

Some doctors across the country have reported delays and cancellations of tests, as well as substitutions of medical isotopes — radioactive combinations of protons and neutrons that are artificially produced.

These isotopes work well in cardiac diagnosis, for example, because they mimic the biological process of blood flowing to the heart once they're injected in a patient and act as tracers for special cameras as they dissipate. That shows where and how fast blood is flowing, unlike X-ray or CT scans that take anatomical snapshots that show if there is a blockage but not how obstructed the vessel is.

Some technetium has been available for cardiac testing, but many doctors returned to an older isotope, thallium, though they say that means about 25 percent to 30 percent more radiation for patients. It puts off less energy so it can't be used on the obese, which constitutes a growing number of patients. And doctors also say the lower-quality images could lead to more diagnoses of heart trouble when there is none and, perhaps, more unnecessary procedures such as cardiac catheterizations.

Even doctors at large academic institutions such as Maryland and Johns Hopkins locally and the Mayo Clinic have felt the technetium pinch, though they have several alternatives. Each, however, has benefits and drawbacks.

These facilities, for example, have special generators that can produce different isotopes, such as rubidium, which makes clear images even on obese patients. But Dilsizian at Maryland said it costs $30,000 a month to run the generator. There also are a limited number of the cameras across the country needed to snap the images — about 1,600 so-called PET cameras compared with 12,000 SPECT cameras, which capture thallium and technetium.

Doctors at such institutions also are just beginning to use other testing methods that involve magnetic resonance imaging (MRIs) and computed tomography (CT scans), but they are still new and require specific expertise, said Dr. Richard George, an assistant professor at the Johns Hopkins University School of Medicine and its Heart and Vascular Institute.

There also are other common methods such as echocardiograms, which use high frequency sound waves to produce images, meaning there is no radiation. That may be preferable for young patients. But it can't be used for obese patients and can miss some disease.

Hopkins and Maryland doctors say they have not had to cancel tests and believe they are matching the best available tests to patients. But they prefer to have the technetium back on the job.

"We can still make a diagnosis of the patient," George said. "But we'd like the best image quality possible at the lowest radiation dose."

At the Mayo Clinic in Jacksonville, Fla., doctors have invested in a new camera that more easily picks up radiation and allows doctors to use less technetium. But Dr. Thomas Gerber, a professor of medicine and radiology, said most facilities do not have the latest equipment.

He also preserves technetium by combining isotopes during cardiac tests, using technetium for the stress portion while a patient is on a treadmill increasing his heart rate, and using thallium while the patient is at rest. And other technology is used for other patients.

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