An MRI machine applies radio pulses that cause hydrogen atoms to wobble in a detectable way. The process also deposits heat to tissues. Fost says that MRI scans are generally considered safe, but they can trigger claustrophobia and may cause needless anxiety if they turn up an unexpected quirk that proved benign.
Giedd acknowledges the potential for abuse but sees nothing wrong in his particular case. "If I wouldn't feel comfortable doing something with my own child, then I wouldn't feel comfortable doing it to someone else's child," he says.
The subject herself says she was disappointed to learn there would be no more brain pictures. Now when she visits her father's office, she can only watch. "Sometimes I wish I could do it again to see how I've changed since I was little," she says. But even if the IRB changed its stance, there's a new hitch: Small pieces of metal interfere with the imaging process, and this past November, Sasha got braces.