The hope of the atomic age, when it dawned, was that if radioactivity did not kill mankind, it would cure it. It has done neither, and as time has passed, the fact has become increasingly clear that the greater value of nuclear medicine is in its use as a tool for diagnosis. “Therapy today constitutes no more than 1% of our activities,” said Dr. James Quinn, director of nuclear medicine at Chicago Wesley Memorial Hospital, before a year-end meeting of the American College of Radiology.
Radioisotopes are now commonly introduced into the body’s various systems to allow doctors to trace functions and spot malfunctions with sensitive scanners. But radioactivity is the peril as well as the point of using the particles, reported Quinn, since too much of it during the testing can harm the patient. The ideal, therefore, is to find a radioactive substance with a short half-life that will decay quickly after passing on the information doctors need. The problem is that the unstable substances live so briefly they must be manufactured as short a time as possible before their use.
Enter the radioisotope “cow.” A simple device first developed at the Brookhaven National Laboratory, it takes advantage of the fact that many long-lived radioactive substances can produce short-lived radioactive offspring. The cow consists of an open-ended test tube with various layers of alumina and specially treated glass through which the parent substance is filtered. In the case of a parent such as molybdenum-99 (half-life: 2.8 days), technetium-99m (half-life: 6 hours) is produced, and it accumulates at the bottom of the tube (the cow’s udder). The milked technetium can therefore be created only moments before it is put into a patient, and the doctor can scan its internal path while it is most active; yet within 24 hours, it will have decayed to an undangerous one-sixteenth of its former self. Since patients are far safer, they can take many more such tests, thus vastly multiplying the data with which doctors can find out what is wrong and perhaps even why.
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