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Human Brain Imaging and Radiation Dosimetry of ¹¹C-N-Desmethyl-Loperamide, a PET Radiotracer to Measure the Function of P-Glycoprotein

¹ Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland; and ² PET Department, Clinical Center, National Institutes of Health, Bethesda, Maryland

View larger version (94K): [in this window] [in a new window]   FIGURE 1.  PET images of 11C-dLop in human brain and corresponding MR image. PET images were summed from 0 to 90 min, and pixel values represent mean concentration of radioactivity (%SUV). Coregistered MR images and fused PET and MR images are also shown. Arrows point to choroid plexus on medial surfaces of lateral ventricles and on roof of third and fourth ventricles.

View larger version (6K): [in this window] [in a new window]   FIGURE 2.  (A) Concentration of radioactivity in brain, with () and without () vascular correction, in 4 subjects who had head-dedicated imaging. Symbols represent mean values. SD bars are included for all points after 18 min. Note that SD bars are smaller than symbols for all points after 60 min. (B) Concentration of radioactivity in brain in 8 subjects who had whole-body imaging. Vascular correction of brain activity could not be performed in these subjects, because no blood was collected during scanning. Conc = concentration.

View larger version (17K): [in this window] [in a new window]   FIGURE 3.  After injection of 11C-dLop, radioactivity in pituitary gland () and choroid plexus () peaked quickly and remained stable during course of scan, whereas uptake in venous sinus () and fourth ventricle (i.e., CSF) () peaked quickly and stabilized at lower level. Symbols represent mean values in 4 subjects. For clarity, SD bars are included only after 5 min and for every other time point. Conc = concentration.

View larger version (10K): [in this window] [in a new window]   FIGURE 4.  Concentration of unchanged 11C-dLop in plasma after radiotracer injection. Curve is shown with 2 time intervals (0–5 min and 5–90 min) because of high concentrations at early time points. Each symbol represents 1 of the 4 healthy control subjects. Conc = concentration.

View larger version (7K): [in this window] [in a new window]   FIGURE 5.  (A) Percentage composition of plasma radioactivity over time is shown for 11C-dLop () and total radiometabolites () (n = 4 subjects). Symbols represent mean ± SD, although SD is sometimes smaller than size of symbol. (B) Representative radiochromatogram of plasma at 30 min after injection of 11C-dLop. Parent constituted 88% of total radioactivity. Radiometabolites (A–E) are less lipophilic than11C-dLop. cps = counts per second.

View larger version (39K): [in this window] [in a new window]   FIGURE 6.  Maximal-intensity-projection images of distribution of radioactivity in healthy male subject at 3, 20, and 100 min after injection of 11C-dLop.

View larger version (9K): [in this window] [in a new window]   FIGURE 7.  Uptake of radioactivity in organs that could be visually identified on planar whole-body images. Activity of organ is expressed as percentage of injected activity. Data are mean ± SD in 8 subjects.