Stereo endoscopy as a 3-D measurement tool.

Stereoscopic endoscopes restore much of the sense of depth perception lost in minimally invasive surgery techniques. They also open the possibility of anatomical reconstruction from in-vivo video using established computer vision techniques. However, limitations in computational power, as well as imaging constraints due to specularities, color, and movement, make full three-dimensional reconstruction difficult to achieve in real time. We demonstrate that a subset of this reconstruction problem, the ability to take accurate anatomical measurements, can be trivially achieved using current stereo-endoscopes and well-known algorithms. After careful calibration of the camera pair, we track the surgical instruments, which present the strongest features in the operating scene. The three-dimensional positions of the tips of the instruments are automatically calculated in real-time, and the computation of the distance between them allows for accurate measurements of any anatomical region within reach of the instrument tips.