A substance being studied as a way to find sentinel lymph nodes in some types of skin cancer and breast cancer. It contains a radioactive substance called technetium linked to a substance called dextran. Dextran helps technetium stay in blood and lymph vessels after it is injected. A machine or probe that detects radioactivity shows which lymph nodes near the tumor have 99m-Tc-Dx in them. Also called Tc-99m Dextran and technetium Tc 99m-dextran.