This paper describes the Monte Carlo simulation, using MCNP4C, of a portable instant non-scanning tomography containing five radioactive sources with the same activities and seventy NaI(Tl) detectors constituted of five sets of fourteen detectors, diametrically opposite to each radioactive source. The detector was validated by comparison with the experimental measurements. The full width at half maximum (FWHM) deviation between the experimental and the simulated spectra was 3.5%. A steel pipe of 17 cm??0.5 cm (diameter??thickness) containing water and two dynamic bubbles of 2 cm and 4 cm diameter were simulated. The SIRT algorithm was used to reconstruct the images. The simulated images are presented in frames. On the first frame, no bubble is observed. On the subsequent frames, the growing of the bubbles is observed, reaching the maximum diameter; after that, the bubble begins to decrease progressively, until its disappearance. The measured bubble diameters generated by simulation were 43 ?? 3 mm and 27 ?? 2 mm for the bubbles of 40 mm and 20 mm diameters, respectively. The spatial resolution of the proposed simulated tomography was estimated by the Modulation Transfer Function (MTF), presenting a spatial resolution of 18.3 mm and 20.2 mm for samplings at 137Cs photopeak and full window, respectively.Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)FAPESP: 12/22705-3