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Traditionally, PET scanners have annular lead shielding at the axial ends that extends beyond the crystals to reduce the number of photons from outside of the axial field of view (FOV) hitting the detector. In recent years there has been a trend toward reducing the end shielding in order to increase the patient port diameter of the PET scanner. The reduction of the lead shielding could have performance effects that could affect overall image quality. The University of Pennsylvania has both a Philips Gemini TF Big Bore and a standard Gemini TF, with the major difference between the two systems being the reduction of the end shielding on BigBore. We evaluated the count-rate performance between the two systems to determine differences in performance characteristics. We also performed phantom measurements to determine the impact of performance differences on the scatter correction and reconstructed image quality. While there are differences in the performance of BigBore as compared to TF, the overall image quality of studies obtained on BigBore are comparable to those obtained on TF.