Image Generation of Serotonin Synthesis Rates Using α-Methyltryptophan and PET

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Abstract
We sought to create functional images of the serotonin (5-HT) synthesis rate obtained with alpha-[11C]methyl-L-tryptophan (alpha-MTrp) and PET and standardize them into the stereotaxic coordinate system. Dynamic PET scans were performed in 11 healthy subjects after an injection of alpha-MTrp. Results obtained by the Patlak plot and nonlinear least-squares methods using arterial plasma as input function were compared. The pixel-by-pixel calculation of functional images of 5-HT synthesis was done by the Patlak plot approach, after results were compared by two methods. Input function obtained by combining venous plasma and sinus radioactivities was also evaluated as an alternative to arterial input function. There were no significant differences in 5-HT synthesis between the two calculation methods. The normalized venous input functions gave similar results as the arterial input function. The regional rates of 5-HT synthesis from functional images were not significantly different from those obtained by graphical plotting. alpha-MTrp images could be converted into functional images representing 5-HT synthesis rates in the living brain, facilitating statistical comparison.