Fig. 10
Example of time-activity curves of the gamma-ray monitor detector placed in the PET room (a), the radioactivity concentration of the air in the exhaust duct carried from the PET scanner room (b), and background- and decay-corrected radioactivity curves in the exhaust duct (c). Data were observed during a series of PET examinations involving C15O, 15O2, and C15O2 inhalation on each of two patients. Characters “a” and “b” corresponded to a period when the cyclotron was accelerating a deuteron beam to a target, in which the radioactive gas was not circulated to the PET room during period “a,” but it was circulated to the PET room during period “b.” The three other characters “c,” “d,” and “e” corresponded to the periods of supplying C15O, 15O2, and C15O2 gases to the patient’s facemask, respectively. Leakage of gaseous radioactivity was not detected (n.d.) during the first examination, but was significant in the second examination as shown in (b)