  The novel whole-body PET system based on plastic scintillators is developed
by the {J-PET} Collaboration. It consists of plastic scintillator strips
arranged axially in the form of a cylinder, allowing the cost-effective
construction of the total-body PET. In order to determine properties of the
scanner prototype and optimize its geometry, advanced computer simulations
using the GATE software were performed.
  The spatial resolution, the sensitivity, the scatter fraction and the noise
equivalent count rate were estimated according to the NEMA norm as a function
of the length of the tomograph, number of the detection layers, diameter of the
tomographic chamber and for various types of the applied readout. For the
single-layer geometry with the diameter of 85 cm, strip length of 100 cm,
cross-section of 4 mm x 20 mm and silicon photomultipliers with the additional
layer of wavelength shifter as the readout, the spatial resolution (FWHM) in
the centre of the scanner is equal to 3 mm (radial, tangential) and 6 mm
(axial). For the analogous double-layer geometry with the same readout,
diameter and scintillator length, with the strip cross-section of 7 mm x 20 mm,
the NECR peak of 300 kcps was reached at 40 kBq/cc activity concentration, the
scatter fraction is estimated to about 35% and the sensitivity at the centre
amounts to 14.9 cps/kBq. Sensitivity profiles were also determined.
