Kinetic modeling of Fe-52/Mn-52m-citrate at the blood-brain barrier by positron emission tomography

The kinetics of iron at the blood-brain barrier of the monkey were studied in vivo using positron emission tomography (PET) and the tracer Fe-52/Mn-52 m-citrate. Mn-52m is the beta(+)-emitting daughter nuclide of Fe-52 and the refore contributes to the observed signal and background in the PET images and may influence the quantification of physiological relevant iron paramet ers. The kinetics of pure Mn-52m-citrate at the blood-brain barrier of the monkey were studied experimentally, and the analysis of the data with a rea sonable compartment model led to equal efflux and influx parameters for Mn (1.35 +/- 0.3 x 10(-2) min(-1)). By using complexes between Mn and diethyle netriaminepentaacetic acid, the validity of the proposed model could be con firmed. To describe the observed kinetics of 52Fe/52mMn-citrate, the mangan ese model was coupled to an iron model, which finally allowed the quantific ation of two iron-specific parameters: an input rate into global brain tiss ue of 7.15 +/- 2.6 x 10(-4) min(-1) and a time delay of roughly 24 min to a ccount for the observed activities. The simpler linearization procedure has been proposed and could be applied to all our data sets and is able to rep lace the complicated nonlinear iron/manganese tracer kinetic model neglecti ng any influence of manganese on the analysis.