If you ran a business that depended on a critical component, how would you feel if the supplier were an aging factory-and no other producer existed? Not good probably. But you might feel better if some enterprising engineers invented a way around the bottleneck. And if the new method generated less waste than the old one, so much the better.

That's just what's happened in the case of technetium-99 (Tc-99), a radioactive isotope that is the workhorse of such medical-imaging techniques as single-photon-emission computed tomography. The sole North American source for the isotope is a 40-year-old nuclear reactor in Canada. Temporary shutdowns in 1991 and again last year threatened the supply, sending shock waves through the medical community, says S. James Adelstein, a Harvard University professor of medicine who chaired a 1995 Institute of Medicine report on medical isotopes.