The Radiomicrography of the Autopsy Brain

Abstract

One of the aims of radiography is to be able to magnify the radiographic image even as histologic technics magnify the cellular composition of the gross specimen. Various methods have been employed to achieve this goal: (1) Utilization of a special tube with a small anode producing soft x-rays penetrating the specimen, which lies in close contact with a fine grain photographic plate. (2) Utilization of a point source of x-rays either by means of a pin-hole serving as a secondary focus or by an extremely small focal spot roentgen tube. (3) Utilization of hard x-rays which first penetrate the photographic film, then the sample, and finally strike a heavy metal absorber such as lead. The secondary back-scatter from the lead absorber then penetrates the sample and strikes the film, producing a secondary image. (4) The electron microscope employing beta rays, alpha rays, and similar non-x-ray methods. A recent review of this subject by Bellman is summarized in Figure 1. In most instances, these studies were made on animal tissues other than human. In the angiomicrographic technics, injections can be made in living animals just prior to death, so that ideal distribution of the contrast medium can be obtained. With human tissues, where premortem injections are impossible, the problem is more difficult, and complete perfusion of the vascular system must be obtained prior to the injection of the contrast medium in order to remove the contained blood and insure more complete filling. It is the purpose of this paper to describe such a technic for routine postmortem examination of the brain by radiomicrography. Factors Involved in Radiomicrography with Secondary Magnification 1. Size of the Focal Spot: This must approach pin-point size. 2. Distance Between Focal Spot and Specimen, Between Focal Spot and Film, and Between Specimen and Film: The distance between focal spot and specimen, and between focal spot and film, must be as great as practical so as to reduce distortion to a minimum and yet not prolong exposure unnecessarily. The contact between specimen and film must likewise be maximal to avoid irregular distortion of the image. 3. Thickness and Size of the Sample: So long as large focus-to-object distances are used, good resolution with minimum distortion is obtained even with relatively thick samples. A sample should be thick enough so that a continuity of blood vessels is obtained to permit easier analysis. On the other hand, it must not be too thick, in order to avoid too many superimposed vascular shadows and too much backscatter. The thickness will vary with the tissue being studied and its relative vascularity and density. 4. Spectrum of the X-Ray Beam: The x-ray beam must be soft enough to be partially absorbed by the medium to produce contrast, hard enough to penetrate the section, and of such character that the scattering effect is least disturbing to the image.