A kidney donor is wheeled to an operating room for a transplant at Johns Hopkins Hospital in Baltimore in late June. Brendan Smialowski/AFP/Getty Images hide caption

itoggle caption Brendan Smialowski/AFP/Getty Images

A Beechcraft airplane sprays insecticide over Dallas early Monday morning to curb the spread of West Nile virus. LM Otero/AP hide caption

itoggle caption LM Otero/AP

People wait in line at the Durham County Health Department for the H1N1 flu vaccination in Durham, N.C., in November 2009. Gerry Broome/AP hide caption

itoggle caption Gerry Broome/AP

A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/Wikimedia Commons

Ashley Beecher, 29, and her daughters Annie (on lap) and Charlie. After feeding Annie, Beecher donates her extra supply to the human milk bank at Texas Children's Hospital. KUHF hide caption

itoggle caption KUHF

Childhood obesity is on the rise in many countries and overuse of antibiotics is now on the radar as a possible factor in the epidemic. Here 18-month-old twins are weighed in a nutritionist's office in Colombia. Raul Arboleda/AFP/Getty Images hide caption

itoggle caption Raul Arboleda/AFP/Getty Images

Radiologist Gerald Iba checks mammograms at The Elizabeth Center for Cancer Detection in Los Angeles in May 2010. Damian Dovarganes/AP hide caption

itoggle caption Damian Dovarganes/AP

Dr. Amit Etkin and a research assistant help a participant into the bore of the MRI. Courtesy of the Etkin Lab at Stanford University hide caption

itoggle caption Courtesy of the Etkin Lab at Stanford University