Radioactive 'understudy' may aid medical imaging, drug d...( Broadway stars have understudies. No...)

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 (NIST), 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 yearand this has correspondingly increased the use of fluorine-18, 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 lifea 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 as a calibration surrogate for fluorine-18. This germanium isotope is much longer livedits half-life is 270.95 daysbut its radiation decay characteristics are otherwise similar to fluorine-18. Small differences between measurements of germanium-68 and fluorine-18 can be accounted for throu
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