Stability of alpha-[11C]methyl-L-tryptophan brain trapping in healthy male volunteers

Eur J Nucl Med Mol Imaging. 2005 Oct;32(10):1199-204. doi: 10.1007/s00259-005-1829-5. Epub 2005 Jun 10.


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

Methods: 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 alpha[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 alpha[11C]MT brain trapping in a priori selected VOIs.

Results: alpha[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.

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

Publication types

  • Clinical Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Brain / diagnostic imaging*
  • Brain / metabolism*
  • Brain Mapping / methods*
  • Humans
  • Male
  • Metabolic Clearance Rate
  • Middle Aged
  • Positron-Emission Tomography / methods*
  • Radiopharmaceuticals / pharmacokinetics
  • Reference Values
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Serotonin / metabolism*
  • Tryptophan / analogs & derivatives*
  • Tryptophan / pharmacokinetics


  • Radiopharmaceuticals
  • alpha-methyltryptophan
  • Serotonin
  • Tryptophan