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


CONCLUSIONS
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.
Rosa-Neto
Pedro
P
Department of Neurology and Neurosurgery, McGill University, Montreal, QC, H3A 1A1, Canada.
Diksic
Mirko
M
Leyton
Marco
M
Mzengeza
Shadreck
S
Benkelfat
Chawki
C
D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
D019275:Radiopharmaceuticals; C020774:alpha-methyltryptophan; D012701:Serotonin; D014364:Tryptophan