title: The requirement for constant arterial radioactivity in the C15O2 steady-state blood-flow model.
abstract: This study evaluates the discrepancy between the true CBF value and the CBF value calculated according to the C15O2 steady-state model, for situations where the arterial input function, Ca(t), deviates considerably from its steady-state value, Ca. The fact that arterial input function and tissue O-15 concentration are not independent variables is taken into account. Inconstant or variable arterial input functions are simulated and the corresponding tissue O-15 concentrations calculated. The steady-state CBF values are evaluated for several temporal variations of Ca over the period of imaging, all derived from Ca(t) by simulation of various blood-sampling schemes, and are compared with the true CBF value. The study indicates that reliable CBF values are obtained by the C15O2 steady-state method even under severely impaired "unsteady-state" conditions, provided that either the true average arterial concentration over the entire scan, or the average concentration from multiple arterial samples, is used.
mesh_terms: D001158:Arteries; D001834:Body Water / Q000378:metabolism; D002245:Carbon Dioxide; D002560:Cerebrovascular Circulation; D006801:Humans; D008433:Mathematics; D008955:Models, Cardiovascular; D010104:Oxygen Radioisotopes / Q000097:blood; D014055:Tomography, Emission-Computed / Q000379:methods*
chemical_list: D010104:Oxygen Radioisotopes; D002245:Carbon Dioxide