of the edge enhancement mentioned above is called an edge effect accordingly when phase contrast edge enhancement by refraction of x ray is generated x ray image having high sharpness with sharply described edge can be obtained when x ray source is regarded as a point light source half width e of the phase contrast edge enhancement can be shown by the following formula as shown in fig2 e 2 3 1 r 2 r 1 1 3 r 2 u03b4 2 r 1 2 2 3 1 here r 1 represents a distance between x ray point source 3 and a center of a column of the subject 1 r 2 represents a distance between a center of a column that is assumed as the subject 1 and digital x ray image detector 2 r corresponds to a radius of the subject 1 that is assumed as the column since a blood vessel or a bone is a main substance to constitute the x ray image in a human body a style of the human body can be approximated to the column approximately further concerning u03b4 when refraction index n of x ray is expressed as follows here in medical field or non destructive test the coolidge x ray tube or electro thermal x ray tube 5 is widely used the case in which the coolidge.