1. An image analysis apparatus for detecting a periodic signal corresponding to an arrangement of a grid, which is required to reduce scattered radiation components from an object, from an image obtained by radiation imaging using the grid, said apparatus comprising: a processor; and memory, the processor and the memory being operatively coupled to function as: a setting unit configured to set a plurality of regions on the image; an obtaining unit configured to obtain statistical information of pixel values corresponding to each of the plurality of regions of the image based on the image; a selection unit configured to select at least one measurement region from the plurality of regions based on the statistical information; and a detection unit configured to detect a spatial frequency corresponding to the periodic signal, based on the selected measurement region.