Methods and apparatus for monitoring oxygen saturation levels in tissue aredisclosed. According to one aspect of the present invention, a sensorarrangement for use in an optical imaging system includes a first sourcestructure, a second source structure, and a detector arrangement. The firstsource structure provides a first beam of light and the second sourcestructure provides a second beam of light. The detector arrangement includesdetector structures that have centerpoints, and receives the first and secondbeams of light after the first and second beams of light are reflected off ofan external surface. The detector arrangement is arranged to define a firstaxis that passes through the centerpoint of each detector structure, and adistance from a centerpoint of the first source structure to the first axis isnot equal to a distance from a centerpoint of the second source structure tothe first axis.
