1. An image processing apparatus comprising: reconstruction means for obtaining a reconstructed image of a predetermined structure by reconstructing an image representing the structure after fitting a model representing the structure to the structure in an input image having a periodic noise component, the model obtained by carrying out predetermined statistical processing on a plurality of images representing the predetermined structure without a periodic noise component, and the model representing the structure by one or more statistical characteristic quantities and weighting parameter or parameters for weighting the statistical characteristic quantity or quantities according to an individual characteristic of the structure; noise component extraction means for extracting the periodic noise component in the structure in the input image by calculating a difference value between values of pixels corresponding to each other in the structure in the reconstructed image and in the input image; noise frequency determination means for determining a frequency of the periodic noise component having been extracted; and noise removal means for generating a noise-free image by removing the periodic noise component of the determined frequency from the input image.