19 FEB 2012 - LONDON, GBR - New Zealand's Natasha Hansen (NZL) leads the field during a round of the Women's Keirin at the UCI Track Cycling World Cup, and London Prepares test event for the 2012 Olympic Games, in the Olympic Park Velodrome in Stratford, London, Great Britain (PHOTO (C) 2012 NIGEL FARROW)