Current positron emission tomography is capable for three dimensional data acquisition and reconstruction (3D PET). The main advantage of 3D PET is its detectability for lower tracer concentrations. The images by a 3D PET have better signal to noise ratios compared to those by conventional 2D PET. This point is especially important for the studies of distributions of ligands for neuroreceptors such as F-18 FDOPA and C-11 YM-01951, since these ligands show low accumulation in brain. Reduction of scanning time is useful as well for patients are permitting extended scanning periods