[en] The influence of the numbers of projection of single photon emission computed tomography (SPECT) exerting on a re-constructed image cannot be strictly evaluated by phantom studies. Therefore, we compared re-constructed images of the filtered back projection (FBP) method and the maximum likelihood-expectation maximization (ML-EM) method by using simulation data. Simulation data was entered in the image processing software, and the projection data that changed the numbers of projection was made. Afterwards, reconstructed images of the FBP and the ML-EM methods were compared with respect to contrast, %COV, and the normalized mean square error (NMSE) value. When the numbers of projection of the FBP and the ML-EM method were decreased, all of the contrast, %COV, and the NMSE value were more deteriorated than that of the ideal image. Therefore, the image quality of SPECT improves with both FBP and ML-EM methods when there are many numbers of projection. Moreover, the FBP method was excellent in a cold contrast, and the ML-EM method was uniformly excellent. Therefore, an understanding of features and their inspection are effective for the selection of each image reconstruction method. (author)