Total hip replacement is the well-established surgical method for treatment of hip osteoarthritis and related diseases. The outcome of the procedure is commonly satisfactory and most patients will not need any revision surgery. However, the procedure has its complications, including (1) periprosthetic infection, (2) mechanical loosening caused by wear particles and (3) adverse reaction caused by metal ions released from metal-on-metal bearing surfaces. The unsolved clinical problem is related to the differential diagnosis of these conditions. The purpose of this prospective clinical study is to compare the efficacy of two techniques of PET/CT imaging in the differential diagnosis of these complications. Positron Emission Tomography (PET)/Computed Tomography (CT) imaging, performed during a single day, will include the head-to-head comparison of 18F-Fluoro-D-Glucose (18F-FDG) PET/CT and 68Gallium-citrate (68Ga-citrate) PET/CT imaging.