AAMI: Good ol nuke med not the sharpest modality, but one of the surest

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Transaxial dual isotope - 28.61 Kb

CHARLOTTE, N.C.—Is nuclear medicine really “unclear medicine?” So asked Chris Staley, a nuclear medicine service specialist at Duke University Health System in Durham, N.C., in a June 3 primer on the imaging modality at the 2012 annual conference of AAMI, the Association for the Advancement of Medical Instrumentation.

The play on words, an allusion to nuke med’s reputation for producing highly useful but comparatively indistinct images, was designed to draw in conference attendees considering adding the modality to an in-house portfolio of medical-equipment services.  

Staley explained that 95 percent of nuclear medicine is diagnostic, while most of the 5 percent used therapeutically is generally confined to treating conditions of the thyroid gland, including cancer. In either use, he said, radiation exposure is low—and the technology “can perform studies no other modality can reproduce, such as lung function, heart function, brain function, bone diseases and others.”

Tracing the history of the use of radioisotopes in healthcare, Staley told how physicians and chemists came to identify chemicals that are absorbed by specific organs. The thyroid, for example, takes up iodine, while the brain consumes quantities of glucose, he said, adding that diagnostic radiopharmaceuticals can be used to examine blood flow to the brain, along with functioning of the liver, lungs, heart and kidneys. They can also be used to assess bone growth and to confirm other diagnostic procedures.

The most commonly used isotope in medicine, technetium-99m, was discovered in 1938, two years after the discovery of iodine-131 and several years before such other important isotopes as tritium, carbon-14, fluorine-18 and thallium-201.

Commenting on the safety of the substances, Staley said that radioisotopes can be unsafe by their own nature—“not so much by damage they can inflict, but by the aftermath of a spill.” They are not easily cleaned from the floor or other surfaces, he said, and isotopes spilled on a camera can put the device in downtime for two to three days. 

Technetium is not a standout troublemaker when spilled—unlike mishandled thallium, which “can make an area unuseable for as long as a month, no matter how much scrubbing you do,” said Staley, who added that the technologists who scan the patients often take the lead on isotope procurement and handling.

The first nuclear medicine cameras arrived in the 1950s, Staley said, and were initially deployed to diagnose thyroid disease using iodine-131.

“Technetium 99 has a half-life of six hours—long enough for an exam and short enough to let the patient leave the hospital soon afterwards,” said Staley, who speaks with an engagingly unhurried Southern drawl. Technetium-99m is generated from molybdenum-99, which has a half-life of 66 hours, allowing it to be transported over fairly long distances, he added.

Staley also described the nuke-med process by which crystals produced from sodium iodide convert gamma rays into flashes of light in a phenomenon called scintillation.

Typical areas of service include maintenance and repair of switches and power supplies, as well as motors and controllers. Staley said a consistent quality-control program is essential to ensuring accurate studies, and that particular problems to watch for include damage to detectors, high-voltage drift and degradation of electronic components. He recommended daily tests for uniformity and energy peaking, augmented by weekly testing for linearity, resolution and sensitivity.

Staley concluded by encouraging the group not to be intimidated by nuclear medicine. “Yes, it has software, but nothing unusual, nothing that the average individual cannot take care of,” he stated flatly. “There’s a lot we can do. It’s not scary. A lot of it is common sense. Get some training. With training and common sense, it’s a good, fun modality to work with.”

Asked by an attendee about the biggest difference between nuclear medicine and other imaging modalities, Staley returned to the question with which he led off the discussion—the title of the session, “Nuclear Medicine: Is It Really Unclear Medicine?”

“As someone who used to work in x-ray, I know that it’s really easy for somebody to say, ‘Hey, this film doesn’t look quite right to me; this orthopedic image doesn’t look good,” he said. “Look at x-ray, CT or MR, and how particularly crisp CT is. You don’t see that in nuclear medicine. It’s hard to get past the mindset of needing to see results