The acetate salt of the radioisotope carbon-11. Although the mechanism is unclear, carbon-11 acetate preferentially accumulates in tumor tissue, serving as a tracer for imaging tumors with positron emission tomography (PET). Check for active clinical trialsusing this agent. or A colorless, odorless gas. It is a waste product made by the body. Carbon dioxide travels in the blood from the body’s tissues to the lungs. Breathing out clears carbon dioxide from the lungs.