"In 1996, when Mary Lou Jepsen was in the home stretch of a Ph.D. in engineering at Brown University, she became so ill that eventually she concluded her only option was to drop out of school and move back home to die. Her sickness was a mystery. She had all the signs of AIDS, but she was HIV negative. Her body was covered in sores. She was getting worse every day. Right about the time that Jepsen was running out of hope, she got an MRI scan. There, in that magnet-made map of her body’s water and fat, the problem was obvious: She had a brain tumor. Jepsen underwent surgery to remove the tumor, finished up her Ph.D, and went on to become a hardware visionary at the One Laptop Per Child project, a low-power-display company called Pixel Qi, and then at Google and Facebook. Last year she left Facebook to start Openwater, a company intent on developing a “wearable MRI.” "