Last month, we looked at some of the most exciting entrants in the second annual Google Science Fair. Earlier this week, we had the chance to check out the Science Fair in person and talk to the finalists. Trust us: The 15 finalists, culled from thousands of entrants from over 100 countries, are all incredibly brilliant. But some stood out more than others. So who was the most impressive?

17-year-old Brittany Wenger—the Science Fair’s grand prize winner and the winner in the 17 to 18 age group—has a mouthful of a project: a Global Neural Network Cloud Service for Breast Cancer. The Lakewood Ranch, Florida, resident designed an artificial neural network that can detect 99.1% of malignant breast tumors from Fine Needle Aspirates (FNAs), a breast cancer test that in the past has produced notoriously inconclusive findings for patients.

Artificial neural networks can detect patterns that are too complicated for humans to spot. Wenger’s neural network, which is hosted on the Google App Engine, was tested on FNA data (681 samples) collected by the University of Wisconsin. The result—99.1% sensitivity to malignancy—is 5% higher than the best commercial network’s result.

Wenger’s interest in programming started in the seventh grade. Her artificial neural networks have grown in complexity since then. Says Wenger: “My first neural network played soccer.” Next, Wenger hopes to work with the University of Wisconsin to continue her research, which was inspired by the many people in her life affected by breast cancer. “I want to work on image analysis and expand [the neural network idea] to different types of cancer,” she says.

14-year-old Jonah Kohn was sitting in music class one day, struggling to hear the sounds of his guitar over the din of his classmates, when he and a friend had an idea: Putting teeth on top of a guitar lets the player hear it over loud noise with help from bone conduction. Jonah took it one step further, wondering if the same principle could be used to help people with hearing loss experience music.

Kohn, the winner in the 13 to 14 age group, came up with Good Vibrations—a device that attaches to the user’s body at multiple points and filters sound into various frequencies as it hits different body parts. Essentially, says Kohn, “It helps deaf people hear sounds through vibrations.”

The San Diego, California, resident only started working on the project last September, but he has already shown that Good Vibrations greatly increases deaf subjects’ ability to experience music.

17-year-old Yamini Naidu of Tigard, Oregon, is using computer modeling to develop new treatment pathways for methamphetamine addiction. She’s already well on her way—Naidu has discovered two new binding sites on a receptor protein in the brain that are activated by meth. Her prediction: Certain compounds that bind to these sites (designed by Naidu) can change the binding sites’ shape, preventing meth from sticking. Oregon Health and Science University now has a patent on the binding sites and compounds that she discovered.

“I’ve always wanted to do a project in the field of neurology,” says Naidu, whose uncle passed away from a stroke. This was her first foray into computer modeling (“I spent a summer reading user manuals,” she says), but probably not her last. Next up: Naidu hopes to get a dual MD and PhD and become a neurosurgeon.

Even in rural areas of the developing world with a shortage of doctors, there are plenty of cell phones. Enter 16-year-old Catherine Wong’s “Design and Evaluation of a Cell-Phone Compatible Telemedicine System”—a project that consists of a Bluetooth-enabled wireless transmitter and microprocessor, and circuitry to amplify cardiac activity. The whole thing can transmit real-time EKG images over any Java-enabled cell phone (though static images will show up on more basic phones). “The goal is to get the essence of an EKG,” she says.

So if a doctor isn’t around, an aid worker can simply attach the leads to a patient and the device, and send images to a doctor remotely. The Morristown, New Jersey-based teenager plans to continue work on the project—and on biomedical engineering in general. Wong’s original inspiration: a museum exhibit looking at “Design for the other 90%”.

Designed by 16-year-old Rohit Fenn from Bangalore, India, the Vacu-Flush is a redesigned toilet that takes on two problems in the developing world: the high cost of toilets and the lack of clean water to flush them with. “More people have access to mobile phones than toilets in India,” he says.

The toilet dramatically cuts down on water use with help from a partial vacuum (like those found in airplane toilets). Users push the toilet’s piston all the way down, where it is drawn up into a second chamber. A dip in the piston allows the waste to settle, and it then gets flushed out with water.

Right now, the device costs about the same as a conventional toilet, but Fenn is thinking of making a cheaper plastic toilet to hand out in developing countries.

The majority of the finalists shown here—and most of the finalists in general (8 of 15)—are from the U.S., even though Google accepted submissions from around the world. It’s hard to say exactly why the U.S. residents rose to the top, but Maggie Johnson, a judge in the competition and Google’s director of education and university relations, speculates that it might have something to do with “how the science fair concept is a part of our culture.”

Not all of the thousands of entries to the competition were world-changing, but they did generally show that students around the world are learning the scientific method and coming up with good hypotheses, according to Johnson. As she notes, “The kids who float to the top are the 13-year-old graduate students.”

The finalist winners (Kohn and Iván Hervías Rodríguez, Marcos Ochoa and Sergio Pascual in the 15 to 16 age group) all receive a $25,000 scholarship, a Google Chromebook kit donated to their classroom, an assortment of Lego-related gifts, a Google goodie bag, a “prize experience,” and one year of digital access to Scientific American archives for their schools. Wenger, the grand-prize winner, gets a 10-day trip to the Galápagos Archipelago, a $50,000 scholarship, a set of Lego Mindstorms signed by the design team and Lego’s CEO and owner, first pick of prize experiences, and everything else that the finalists receive.