X-ray contrast medium and X-ray image acquisition method

A method of analyzing a biological sample, comprising:

• penetrating a contrast agent into a biological sample and solidifying the contrast agent to provide a contrast image of the biological sample, the contrast agent comprising wax having a density of 0.95 g/cm3 or less in its solidified state after penetration into the biological sample, and having a melting point of 40° C. to 80° C.;
• melting and resolidifying the solidified contrast agent;
• acquiring an X-ray CT image by irradiating the resolidified biological sample with an X ray having an energy of 4 to 12 keV to acquire an X-ray CT image, the shape of the biological sample being a shape with which a maximum optical path length of the X ray in the biological sample is 2 mm or less;
• specifying a site to be further observed by an optical microscope and/or an electron microscope based on the acquired X-ray CT image and cutting and exposing the site;
• observing the site with the optical microscope and/or the electron microscope;
• and
• combining the X-ray CT image and results of the observation by the optical microscope and/or the electron microscope to analyze the biological sample.