Measurement of dopamine D2 receptors in living human brain using [11C]raclopride with ultra-high specific radioactivity.
BACKGROUND
High specific radioactivity is preferable in the measurement of neuroreceptor bindings with positron emission tomography (PET) because receptor occupancy by mixed cold ligand hampers the accurate estimation of receptor binding. Recently, we succeeded in synthesizing [(11)C]raclopride, a dopamine D(2) receptor ligand, with ultra-high specific radioactivity, i.e., several thousand GBq/μmol. In the present study, we compared the [(11)C]raclopride bindings to dopamine D(2) receptors between radioligands with ultra-high specific radioactivity and ordinary high specific radioactivity in healthy human subjects.


METHODS
Two PET studies using [(11)C]raclopride with ultra-high specific radioactivity (4302-7222 GBq/μmol) or ordinary high specific radioactivity (133-280 GBq/μmol) were performed on different days in 14 healthy men. Binding potential (BP) was calculated by the simplified reference tissue method, peak equilibrium method, and area-under-the-curve method for each region-of-interest using time-activity data in the cerebellum as a reference brain region.


RESULTS
BP values for radioligands with ultra-high specific radioactivity and ordinary high specific radioactivity calculated by the simplified reference tissue method were 4.06 ± 0.29 and 4.10 ± 0.25 in the putamen, 0.44 ± 0.07 and 0.47 ± 0.07 in the thalamus and 0.37 ± 0.06 and 0.38 ± 0.06 in the temporal cortex, respectively (mean ± S.D.). No significant difference in BP was observed between ultra-high specific radioactivity and ordinary high specific radioactivity in any of the brain regions.


CONCLUSIONS
BP values of [(11)C]raclopride with ultra-high specific radioactivity did not differ from those with ordinary high specific radioactivity in the measured brain regions, including striatal and extrastriatal regions.
Fujimura
Yota
Y
Molecular Neuroimaging Group, Molecular Imaging Center, National Institutes of Radiological Sciences, Inage-ku, Chiba, 263-8555, Japan.
Ito
Hiroshi
H
Takahashi
Hidehiko
H
Yasuno
Fumihiko
F
Ikoma
Yoko
Y
Zhang
Ming-Rong
MR
Nanko
Shinichiro
S
Suzuki
Kazutoshi
K
Suhara
Tetsuya
T
D000328:Adult; D001923:Brain Chemistry; D002250:Carbon Radioisotopes; D018492:Dopamine Antagonists; D006801:Humans; D008024:Ligands; D008279:Magnetic Resonance Imaging; D008297:Male; D049268:Positron-Emission Tomography; D020891:Raclopride; D017448:Receptors, Dopamine D2 / Q000032:analysis*; D055815:Young Adult
D002250:Carbon Radioisotopes; D018492:Dopamine Antagonists; D008024:Ligands; D017448:Receptors, Dopamine D2; D020891:Raclopride