PET-microdosing

Lappin G, Garner RC. Big physics, small doses the use of AMS and PET in human microdosing of development drugs. Nat Rev Drug Discov 2003 2 233 0. 

Since the doses are very small, conventional LC-MS techniques are sometimes not sensitive enough to assay samples from microdosing studies. Often accelerator mass spectrometry (AMS) and positron emission tomography (PET) are required for obtaining PK and distribution information, respectively. As described in Section 5.4, although AMS is capable of quantifying 14C-labeled compounds with attomole (10 18M) sensitivity, the technique is not useful for distinguishing between an NCE... 

Metabolism. PET can only measure radioactivity and in order to be able to evaluate those PET data, information about the chemical form of the measured radioactivity is important. Determination of the fraction of intact tracer in plasma and in the target organ in animal experiments can give the required information. The occurrence of labeled metabolites should be assessed at different time points in the human microdosing study. 

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