PARIS (Reuters) - Scientists are due to unveil some of the secrets behind Western art's most enigmatic smile this week, when they present the findings of the most extensive three dimensional scan ever undertaken on the Mona Lisa. Leonardo da Vinci's 16th century masterpiece, perhaps the world's most famous painting, is considered a milestone in the art of portraiture and an icon of European culture. A comprehensive examination of the work, painted at some time around 1503-06, was undertaken in 2004, using special 3D technology developed by scientists from Canada's National Research Council (NRC). The scientists scanned the picture on...