Though other scientists have attempted to use PET to noninvasively monitor maternal-fetal drug exchange and pharmacokinetics (how quickly a drug is taken up and distributed among the body's organs), the PET technique alone did not provide adequate anatomical detail of the tiny fetal organs. The current study combined PET with high-resolution magnetic resonance imaging (MRI) to track cocaine pharmacokinetics down to the level of the placenta and individual regions of the fetal brain.
"The MRI images, which have the necessary detail, served as a high-resolution anatomical template onto which we 'overlaid' the PET pharmacokinetic data using sophisticated computer techniques," Benveniste said. "The resulting images gave us the best of both worlds and allowed us to look at cocaine uptake and distribution in the mother and fetus simultaneously," she added.
The animals were anesthetized prior to scanning. MRI scans were performed first, followed by PET. For the PET study, each animal was injected with a trace quantity of cocaine--less than 10 micrograms, which is not enough to cause pharmacological effects. The injected cocaine had previously been "labeled," or "tagged," with a short-lived radioactive form of carbon (carbon-11). This radiotracer emits a signal that is picked up by the PET scanner, which takes snapshots of the tracer's location over time to show how much and how quickly the cocaine (and/or the metabolic byproducts that retain the carbon-11) enters and clears the various organs. The radiotracer decays and completely clears from the animal's body in about two hours. After the procedure, the animals were returned to their social colony to deliver their offspring.
The combined images show that cocaine and/or its labeled metabolites readily cross the placenta. But the cocaine uptake distribution pattern observed in the fetus was
Source:Society of Nuclear Medecine