Many will remember the segment of "The Sorcerer's Apprentice" in the Disney film Fantasia; it is a perfect metaphor for medical imaging as it stands today. The apprentice magician tests his nascent skills at sorcery by bringing common household items to life and putting them to work. At first, things go well, but eventually he loses control, and chaos ensues.

Medical imaging, too, could spin out of control. The benefits of imaging are undeniable. In the past thirty years, innovations like CT, MRI, and PET scanning have not only markedly reduced clinical risk for patients but have...