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  • Title: Postinjection L-phenylalanine increases basal ganglia contrast in PET scans of 6-18F-DOPA.
    Author: Doudet DJ, McLellan CA, Aigner TG, Wyatt R, Adams HR, Miyake H, Finn RT, Cohen RM.
    Journal: J Nucl Med; 1991 Jul; 32(7):1408-13. PubMed ID: 1906094.
    Abstract:
    The sensitivity of 18F-DOPA positron emission tomography for imaging presynaptic dopamine systems is limited by the amount of specific-to-nonspecific accumulation of radioactivity in brain. In rhesus monkeys, we have been able to increase this ratio by taking advantage of the lag time between 18F-DOPA injection and the formation of its main metabolite, the amino acid 18F-fluoromethoxydopa, the entrance of which into brain is responsible for most of the brain's nonspecific radioactivity. By infusing an unlabeled amino acid, L-phenylalanine, starting 15 min after 18F-DOPA administration, we preferentially blocked the accumulation of 18F-fluoromethoxydopa by preventing its entrance into brain through competition at the large neutral amino acid transport system of the blood-brain barrier. This method appears as reliable as the original and more sensitive, as demonstrated by the comparison of normal and MPTP-treated animals under both conditions.
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