PET tracer


Tracer is a positron emitting isotope labeled molecule, molecular probe, that is either structurally related to the natural substrate (tracee) or involved in the dynamic process.

Administering only trace amounts (i.e. with a high specific activity) ensures that radiopharmaceutical (radioligand) does not cause any unintentional pharmacological or systemic effects. The system needs to be kept in dynamic equilibrium during the PET study, so that the only thing that is changing is the concentration and distribution of our radiopharmaceutical. When this is the case, then the processes can be described with first-order rate constants, and we can calculate results using usual mathematical methods.

Trace amount

Tracer is introduced to system in a trace amount:

Higher than tracer doses

Higher radioligand masses can be intentionally administered in certain study protocols, for example to measure receptor Bmax and KD separately.

See also:


Huang SC., Carson R.E., Phelps M.E. (1983) Tracer Kinetic Modeling in Positron Computed Tomography. In: Lambrecht R.M., Rescigno A. (eds.) Tracer Kinetics and Physiologic Modeling. Lecture Notes in Biomathematics, vol 48. Springer, Berlin, Heidelberg. doi: 10.1007/978-3-642-50036-7_6.

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Updated at: 2019-03-24
Created at: 2013-12-20
Written by: Vesa Oikonen