Searching for sentinel lymph nodes

When cancer starts spreading to other parts of the body via the lymphatic system, the cancerous cells first pass through the lymph nodes closest to the carcinoma. These nodes are therefore called sentinel lymph nodes. For various types of cancer, while the tumor is being surgically removed, the sentinel lymph nodes are also checked for cancerous cells. These lymph nodes are therefore removed and undergo microscopic examination. If no cancerous cells are found, lymph nodes located further from the carcinoma may remain in the body, so that the lymphatic system can carry on functioning to a large extent.

To date, a nuclear medical technique has been used in routine clinical practice to find the sentinel lymph nodes. Medical research has meanwhile shown that it is possible to use the fluorescent contrast agent indocyanine green instead, which could help to reduce the application of radioactive contrast agents. Detecting the fluorescence in the tissue requires a sensitive camera system.

Within the scope of a project funded by the Federal Ministry of Education and Research (FKZ 03V0270), PTB has developed a camera system based on a small camera that does not necessitate cooling. This device can be handheld and can therefore be taken directly to the tissue to be examined. The fluorescence in the tissue is excited by means of light-emitting diodes (LEDs) arranged in a circle around the camera lens. Together with the fluorescence image, an anatomic image is taken in which the fluorescent area is highlighted in pseudo colors to show the physician where the sentinel lymph nodes are located.

This camera system has been successfully tested within the scope of a feasibilexity study at the Department of Gynecology of the Charité university hospital, Campus Virchow, in Berlin. This study involved the examination of 16 female patients with carcinomas of the following types: vulvar, cervical, endometrial and ovarian cancer. It was demonstrated that the sensitivity of the camera system was sufficient to image both the lymph nodes themselves and the lymphatic vessels.