In 1975, Elias Zerhouni, at age 24, came to the United States from Algeria with $369 in his pocket. He had taught himself just enough English to pass an equivalency exam. A recent graduate of the University of Algiers medical school, he had come to take up a residency in radiology, hardly considered a cutting-edge field of medicine at the time. As it happened, he arrived at the dawn of a revolution in medical imaging, one that saw the development of ultrasound, CAT scan and MRI. Zerhouni would become one of the field's leading innovators. In 2002, President George W. Bush appointed...