Using instrumentation built in collaboration with JLab

CWM researchers study radiation blockers while conducting nuclear imaging of iodine uptake

The research, performed at CWM with a Jefferson Lab and CWM-built medical imaging system, involves investigational studies of mice. Bob Welsh, a JLab/CWM jointly appointed professor, is one researcher working on the project. The research demonstrates that scientists can learn about how the body uses certain substances of interest -- such as insulin, the fat-regulating protein leptin, and a wide range of other biological compounds -- by tracking how these substances move through the body of a mouse.

The way one can follow these substances is by attachment of a radioactive isotope of iodine, Iodine-125, which emits a low-energy gamma ray which can be tracked with the very precise detectors that have been designed and built by the JLab Detector Group. The thyroid needs iodine to regulate metabolism and is unable to distinguish between regular dietary iodine and ingested radioactive iodine. So the researchers weren't surprised when, in the course of the project, they noticed that the rodents' thyroids always absorbed a significant amount of radioactive iodine. In addition to being potentially bad for the mice, the thyroid's absorption of radioactive iodine made the images difficult to interpret and could provide false-positive readings or possibly obscure substantial iodine uptake in nearby tissues.

The team was aware that potassium iodide (KI) was the FDA-recommended drug for blocking radioactive iodine absorption by the thyroid in humans in the event of a nuclear accident. Thus the scaled FDA dose was administered to the mice prior to imaging with I- 125. CWM undergraduate William Hammond, who presented the team's findings at the American Physical Society (APS) April 2005 Meeting, participated in this phase of the research for his senior thesis project. The researchers started with the potassium iodide dose that's recommended for humans in the event of a nuclear incident, 130 mg (milligrams), scaled to the mass of the mouse. They administered a solution of potassium iodide to the mice, injected the radioiodine for imaging an hour later, and then imaged the mice. "What we noticed was that the dose that was the exactly scaled human dose did not completely block the uptake of radioiodine. But when we tried three times, five times, 10 times the scaled human dose, we obtained results indicating that 10 times the scaled human dose blocks 1.5–2 times better, though five times the scaled dose is just about as good as 10 times," Welsh explains.

The researchers recognized that the extra benefit gained by the largest potassium iodide dose administered could in some cases be outweighed by potential side effects. To protect their mice in future imaging studies, they're planning to use the potassium iodide dose that's five times the scaled-down human dose.

"When it comes to small animals, I think the results from this research should be taken into consideration when planning future work. But, as for larger implications," Welsh notes, "the results from this study cannot simply be applied to humans. Instead, the results could be indicating that a mouse's metabolism is so different from a human's that you can't just scale the human dose down for mice."

This research was made possible by a collaboration of JLab Detector Group scientists: Drew Weisenberger, Randolph Wojcik, Vladimir Popov, Brian Kross and Stan Majewski; JLab/CWM scientist Robert Welsh; and CWM physicists Julie Cella, Coleen McLoughlin, Kevin Smith and William Hammond; biologists Eric Bradley and Margaret Saha, and CWM applied science graduate student Jianguo Qian. The work was supported by the National Institutes of Health, the Department of Energy and the Howard Hughes Medical Institute.