A method of administration of a substance intended to introduce a steady state concentration in plasma. An initial bolus is given, followed by an extended infusion at a much slower rate. An optimal ratio of bolus to infusion rate is chosen to induce steady state as rapidly as possible. For PET imaging, the resulting steady state allows investigators to infer equilibrium constants from concentration ratios. The pharmacokinetics of many radi-oligands, relative to the decay rate of the isotope, are too slow for this method to be practical. But for those radi-oligands amenable to it, the bolus plus constant infusion method has several advantages, including robust parameter estimates and less vulnerability of outcome measures to errors produced by changes in cerebral blood-flow rates than the bolus approach.
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