Fig. 1

The used freehand SPECT system used for laparoscopic sentinel lymph node detection. The system consists of an optical tracking system including the data-processing unit (part A), attached to an optical camera (part B) that is placed above the patient (similar to an operating light), and a hand-held gamma probe (part C) with little spheres serving as an optical reference (part C). The gamma probe is connected to a standard gamma detector (part D) used for sentinel lymph node biopsy. An optical patient reference (little spheres shown in part E) is taped on the patient’s skin of the left lower abdomen. The optical tracking system determines the position and orientation of the gamma probe with the help of infrared light. The infrared light emitted by two light sources adjacent to the optical camera (part B) is reflected by three sphere markers, detected by the optical camera, and converted to an electrical signal that is processed in the data-processing unit