It is a gamma ray detector. It detects gamma radiation from a radioactive liquid (marker) which is injected around the tumor site, under the patient's skin. The marker migrates to the lymph nodes (drainage points for the lymphatic system), making it possible for the Gamma Finder® to pinpoint the nodes.

The surgeon can then use the device to determine which nodes are the most likely affected by the cancer. The primary node in the lymphatic drainage chain near the tumor is known as the sentinel node.

With the help of the Gamma Finder® only the sentinel node is removed, allowing diagnosis with minimal trauma to the body.