Scientists at Washington University Medical Center in St. Louis, Missouri, are testing a new breed of linear accelerator that could one day supplant the conventional cyclotron for preparation of radiopharmaceuticals used to produce images in the human body with positron emission tomography (PET). The prototype device, an outgrowth of military technology, is called a Tandem Cascade Accelerator (TCA). Its developers say it is more cost-effective and less complex than a cyclotron. And it promises not only to make PET imaging more accessible for doctors and patients, but ultimately to lower the cost of a clinical PET exam (about $2,000) by as much as 25%.