Last updated: 02/17/2009

A sentinel lymph node biopsy is done in two stages. In the first part of the procedure, which takes one to two hours, the patient goes to the nuclear medicine department of the hospital for an injection of a radioactive tracer known as technetium 99....

A doctor who specializes in nuclear medicine first numbs the area around the tumor with a local anesthetic and then injects the radioactive technetium. He or she usually injects a blue dye as well. The doctor will then use a gamma camera to take pictures of the lymph nodes before surgery. This type of imaging study is called lymphoscintigraphy.

After the lymphoscintigraphy, the patient must wait several hours for the dye and the radioactive material to travel from the tissues around the tumor to the sentinel lymph node. He or she is then taken to the operating room and put under general anesthesia. Next, the surgeon injects more blue dye into the area around the tumor. The surgeon then uses a hand-held probe connected to a gamma ray counter to scan the area for the radioactive technetium. The sentinel lymph node can be pinpointed by the sound made by the gamma ray counter. The surgeon makes an incision about 0.5 in long to remove the sentinel node. The blue dye that has been injected helps to verify that the surgeon is removing the right node. The incision is then closed and the tissue is sent to the hospital laboratory for examination.