In 1977, Raymond Damadian and a team of graduate students put together the first whole-body MRI scanner, which they dubbed the "Indomitable." Damadian volunteered himself as the first guinea pig. With veiled trepidation, he sat down on the movable platform inside his shiny, 1 1/2-ton contraption and turned it on. After hours of tinkering, there was no signal. Eventually it occurred to the team that Damadian's corpulence might be preventing the creation of an image, and, with disappointment, they called a halt. For seven weeks after the test, graduate student Larry Minkoff keenly monitored his boss, watching for any odd behavior or ailment. Detecting none, he offered his own, leaner, torso to science. On July 3, 1977, nearly five hours after the start of this test, Indomitable achieved the first human scan and became the first MRI prototype.

Source: http://www.smithsonianmag.si.edu