Radioactive 'Understudy' May Aid Medical Imaging, Drug Development

Broadway stars have understudies. Now, an increasingly popular radioactive isotope has its own stand-in. Developed in part by researchers at the National Institute of Standards and Technology, the substance might ultimately improve medical imaging, speed up clinical trials of many drugs and facilitate efforts to develop more individualized medical treatment.

The number of medical images obtained through the technique known as positron emission tomography (PET) is increasing at a rate of 20 percent a year—and this has correspondingly increased the use of fluorine-18 (¹⁸F), the radioactive isotope of choice in the vast majority of PET procedures. Injected into the bloodstream while bound to “carrier” molecules, fluorine-18 lights up the body during PET scans to perform such jobs as revealing tumors, monitoring heart activity and determining which regions of the brain are active during certain tasks.

However, fluorine-18 has a very short life—a batch of the stuff decays to half its initial quantity in fewer than two hours, and less than one-ten-thousandth of the original amount is left after a single day. Because the stuff decays so quickly, it is not possible for a single central lab to make precise measurements on fluorine-18 solutions and then distribute them to far-flung centers to calibrate PET machines. This lack of a “standard reference” for fluorine-18 means that PET-related measurements from center to center, from patient to patient, and even in the same patient over time, are difficult or impossible to compare with one another.

NIST researchers, collaborating with an Ohio-based nuclear medicine company called RadQual, have turned to germanium-68 (⁶⁸Ge) as a calibration surrogate for fluorine-18. This germanium isotope is much longer lived—its half-life is 270.95 days—but its radiation decay characteristics are otherwise similar to fluorine-18. Small differences between measurements of germanium-68 and fluorine-18 can be accounted for through the use of mathematical “conversion factors.”

Germanium-68 never would be used in actual PET procedures; it would only be used to calibrate the machines properly, enabling more accurate measurements of the fluorine-18 isotopes. Although germanium-68 has been used for performing corrections on PET scanners, the industry has lacked a nationally traceable standard reference material for instrument calibration.

NIST researchers have calibrated solutions of germanium-68 that could become the basis of a new standard reference material for this isotope. The next phase of this project involves working with RadQual to calibrate a new “mock” syringe standard that would use germanium-68 embedded in an epoxy to simulate fluorine-18 in a syringe.

This would help researchers more accurately determine the amount of fluorine-18 to be injected into patients during the PET procedure so as to minimize radiation dose while still producing the best image. NIST is also working independently on a ⁶⁸Ge-based PET “phantom” that can be used to calibrate PET scanners in a way that is traceable back to NIST.

The first commercial products from this collaboration may be reaching PET centers later this year. By giving doctors more accurate results on how specific patients are responding to cancer treatments and providing more precise indications earlier in clinical trials as to how individual patients are metabolizing particular drugs, better standards for PET imaging may hasten the arrival of “individualized” medicine.

Source: NIST

Related stories:

Facebook rekindling long-lost friendships
It was the first message Marlee Wallingford ever received on Facebook. And it was a simple one: "Did you go to Salisbury Central School in 1968?"
China vows overhaul of 'chaotic' milk industry
(AP) -- China's Cabinet vowed a complete overhaul of the scandal-ridden dairy industry Monday, pledging to inspect every link from the farm to the dinner table to try to restore public trust in Chinese-made food products.
Doctors: No hamsters or exotic pets for young kids
(AP) -- Warning: young children should not keep hedgehogs as pets - or hamsters, baby chicks, lizards and turtles, for that matter - because of risks for disease.
Calming your thoughts through mindfulness
Our worries. They're crescendoing like the finale of Beethoven's "Ninth": Bailouts, buyouts. Recession, depression.
Do 'light' cigarettes deliver less nicotine to the brain than regular cigarettes?
For decades now, cigarette makers have marketed so-called light cigarettes — which contain less nicotine than regular smokes — with the implication that they are less harmful to smokers' health. A new UCLA study shows, however, that they deliver nearly as much nicotine to the brain.
Bison roam prairie at renowned physics laboratory
The herd appeared docile, grazing quietly on the lush prairie and flicking away flies with their tails. But John Plese knew better. He dared not get out of his truck, parked just feet from a 1,500-pound bull. If there's one thing he's learned as Fermilab's chief herdsman, it's this: Never let your guard down around a bison.
Fishy diet in early infancy cuts eczema risk
An infant diet that includes fish before the age of 9 months curbs the risk of developing eczema, indicates research published ahead of print in the Archives of Disease in Childhood.
Open cancer surgery set to become a thing of the past
The surgeon's knife is playing an ever smaller role in the treatment of cancer, as it is replaced by increasingly efficient and safe radiation therapy techniques. Progress in radiation technology will also lead to better detection rates for cancer. This is according to Professor Freek Beekman, who will give his inaugural speech at Delft University of Technology on Wednesday, 24 September.

News discussion:

Medicine & Health news