Stability of α-[11C]methyl-l-tryptophan brain trapping in healthy male volunteers

  • Pedro Rosa-Neto
  • Mirko Diksic
  • Marco Leyton
  • Shadreck Mzengeza
  • Chawki Benkelfat
Original Article



The purpose of this study was to assess the reproducibility in healthy volunteers of α-[11C]methyl-l-tryptophan (α[11C]MT) brain trapping imaging with positron emission tomography (PET), using volumes of interest (VOIs) and voxel-based image analysis.


Six right-handed healthy male volunteers (34.3±10.9 years) with a negative family history for psychiatric disorders were scanned twice in the resting condition, 22±17 days apart. An unbiased semiautomatic segmentation of the brain was used to define VOIs. The trapping constant K* (ml g−1 min−1) for α[11C]MT was calculated for the whole brain and seven brain regions using the graphical method for irreversible tracers. In addition, parametric maps of K* were obtained from dynamic scans using the same method. Comparison of test and retest K* functional images was performed using SPM99. Student’s paired t statistic was applied for comparisons of α[11C]MT brain trapping in a priori selected VOIs.


α[11C]MT brain trapping in VOIs showed a mean variability 2.6±1.8% (0.3–5%) for absolute and 1.5±2.1% (1.4–4.1%) for normalized K*. Intraclass correlations between test and retest conditions were 0.61±0.34 for absolute K* values and 0.73±0.20 for K* values normalized by global mean. SPM99 analysis using a height threshold of p=0.05 (two tailed) and an extent threshold of 100 voxels showed no significant differences between scans.


Rest measurements in healthy male volunteers of the trapping constant for α[11C]MT, using PET, appeared to be stable during an average interval of 3 weeks.


PET α[11C]MT  Brain trapping Serotonin synthesis Test–retest 



This research was supported in part by grants from the NIH, CIHR, and FRSQ.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Pedro Rosa-Neto
    • 1
    • 2
  • Mirko Diksic
    • 1
  • Marco Leyton
    • 1
    • 2
  • Shadreck Mzengeza
    • 1
  • Chawki Benkelfat
    • 1
    • 2
  1. 1.Department of Neurology and NeurosurgeryMcGill UniversityMontrealCanada
  2. 2.Department of PsychiatryMcGill UniversityMontrealCanada

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