Technetium Tc 99m sulfur colloid
Technetium 99m sulfur colloid is a radiopharmaceutical diagnostic agent used in the evaluation of various conditions including lymph node metastases in breast cancer, detection of shunt patency, imaging of reticuloendothelial cells for assessment of liver function, and studies of esophageal transit and gastroesophageal reflux.  Following injection or oral administration, single photon emission computer tomography (SPECT) imaging is performed using a gamma camera to detect technetium-99m decay. This is possible as Technetium-99m decays by isomeric transition to technetium-99 through the release of a gamma ray. Depending on site of administration and intended usage, Technetium 99m sulfur colloid enters the capillaries and is transported to the lymph nodes (subcutaneous injection), mixes with peritoneal fluid (intraperitoneal injection), is taken up by reticulocytes (intravenous injection), or enters the gastroesphageal tract (oral administration).