To measure the concentration of elements and/or element composites in a subject which is composed of elements and/or element composites by position resolution.

To measure the concentration of n elements and/or element composites in a subject composed of n elements and/or element composites, plural digital X-ray images are projected at once or one after another by a X-ray device (8) in at least one range of the subject (11) with m (≥n) different spectral distribution of X-ray beam S(E) and/or detector sensitivity D(E) under the same geometry condition to obtain m attenuation values μi of each pixel showing same position in the X-ray image. The concentration cj of n elements and/or element composites are calculated about at least one pixel from each m attenuation values μi by considering known absorption spectrum kj(E) of n elements and/or element composites and m (≥n) different spectral distribution of X-ray beam S(E) and/or detector sensitivity D(E).