Ammonia (N-13)

NH3 is a PET tracer used for studies of myocardial perfusion imaging. It is produced in a cyclotron by proton irradiation of the enriched water of the oxygen-16. Ammonia (N-13) is administered intravenously, at a dose of 10-20 mCi (370-740 Mbq) in adults; its physical half-life is 10 minutes.

Extraction and retention 

Ammonia, at physiological pH, is found in its cationic form, NH4(ammonium ion); it is, therefore, probable that it passes the cell membrane of the myocyte through the sodium-potassium pump (Na/K) active transport mechanism. Inside the cell, it is then converted, together with glutamic acid, into glutamine (N-13).