Positron emission tomography (PET) is the most state-of-the-art clinical examination method in the field of nuclear medicine imaging technology. The PET is one of the best tools for tumor diagnosis and guidance in the clinical treatment. The source data that are obtained by PET, need to be processed into a sinogram form data which can be used for image reconstruction. Parallel beam tomographic reconstruction and fan-beam tomographic reconstruction are two methods of imagetomographic reconstruction, respectively, corresponding to parallel beam data processing and fan beam data processing. The processing of the original data is inevitable to destruct the integrity of original data. Nowadays, the PET is a commonly used method of parallel beam image reconstruction. Parallel beam data processing will change original data by data interpolation operation, and the fan beam data processing avoids data interpolation operation. In this paper, we study the influence of data interpolation on PET image reconstruction by comparing the results obtained by the parallel-beam image reconstruction with those obtained by fan-beam image reconstruction.