text: For example, a new radiolabelled compound is injected intravenously into a group of 16-20 rodents (typically mice or rats).  At intervals of 1, 2, 4, and 24 hours, smaller groups (4-5) of the animals are euthanized, then dissected.  The organs of interest (usually: blood, liver, spleen, kidney, muscle, fat, adrenals, pancreas, brain, bone, stomach, small intestine, and upper and lower large intestine, a tumor if present) are placed in pre-weighed containers and weighed, then placed into a device that measures radioactivity (e.g. gamma radiation). Normalizing the tissue radioactivity concentrations to the injected dose gives values in units of percent of the injected dose per gram of organ or biological tissue. The results give a dynamic view of how the compound moves through the animal and where it is retained.