Radioactive sprinkles keep machines true.

Radioactivity-detecting medical scanners, such as positron emission tomography (PET) imagers, are becoming so sharp-eyed that it's more challenging than ever to find the limits of the machines' vision. Doing this requires uniform radiation sources smaller than the minimum-size object the scanners are supposed to discern. Without such verification, uncertainty about the resolution of the machines' detectors could lead to misinterpretations of scans.

Medical physicists have made test items for scanners by irradiating fine metal wires or other objects in nuclear reactors or particle accelerators, but that's not cheap or convenient.

Now, an Australian team has come up with a promising alternative. Dale L. Bailey and his colleagues at the Royal North Shore Hospital in Sydney have created radioactive balls the size of candy sprinkles by dipping porous beads into a saline solution containing the radioisotope technetium-99m. The beads themselves are commercially available spheres of zeolite--a class of porous compounds of silicon, aluminum, and oxygen (SN: 5/17/03, p. 318).

"The beauty of [these] sources ... is that they're cheap and easy to make in the hospital or lab," Bailey says. He and his colleagues describe their work in the Feb. 7 Physics in Medicine and Biology.--P.W.