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PET image quality (IQ) is altered by biological and physical parameters, like the scanner sensitivity, tomographic uniformity, contrast, spatial resolution and reconstruction algorithms. In this work we analyze the differences, advantages and disadvantages between NEMA NU-2 and AAPM TG 126 methods for PET IQ. Measurements were performed on a Siemens mCT Biograph PET-CT System and two phantoms were used: IEC/NEMA Body Phantom (for NEMA measurements) and PET ACR Phantom (for AAPM measurements). 18-Fluorine (18F) was used as the radioactive source (radiopharmaceutical) and all data were reconstructed with UHD: PSF + OSEM + TOF algorithm, iteration number and FWHM were varied. Our results indicates a dependence of contrast with reconstruction parameters. When contrast on a PET image increase, background noise and partial volume effect also increase. Three indicators were measured and graphed, drawing ROIs with an only one performance with NEMA, however, only contrast was measured with AAPM TG 126 protocol and data were compared with the reported limits of this protocol. It indicates that evaluation of IQ on NEMA NU-2 is better than AAPM TG 126, because of the different indicators reported, however AAPM TG 126 analysis is easier to evaluate if system does not have the NEMA quality control acquisition. [ABSTRACT FROM AUTHOR]