X-Ray Methods in Histochemistry

Abstract

A survey is given of the various X-ray methods used in histochemical analysis. The techniques of the formation of microscopic X-ray absorption images are discussed. Direct microradiography of histological sections using fine grained photographic emulsions can give as good resolution as 1 u. with simple equipment. The X-ray microscope is expected to have a much better resolving power. Absorption images of cellular structures recorded with soft X-rays, 8-12 A. in wavelength, permit the determination of the mass (dry weight) in these structures. The accuracy of this cytological X-ray weighing technique is discussed. It is emphasized that the preparation of the biological material for such histochemical analysis introduces a considerable error. Absorption measurements with monochromatic X-rays of suitable wavelengths permit an elementary analysis on a histological level of certain elements but this method has very restricted applications. The accuracy of the X-ray absorption methods is relatively good when applied to ideal objects. The important point is that the accuracy of the method has to be determined for each problem under study before valid conclusions can be drawn. Methods utilizing X-ray emission (X-ray fluorescence methods) can be applied to certain biological problems. Especially the curved crystal X-ray image spectrograph seems to offer a promising approach to certain types of histochemical analyses. In the field of micro-X-ray diffraction new techniques have been developed recently which permit the recording of X-ray diffraction patterns of microscopic structures. Finally microradiological techniques applied to the study of the capillary circulation are examined critically. The problem of "microangiography" is that of administering the X-ray contrast to the blood vessel system without introducing artefacts.