Microscopic Historadiographic Technic for Locating and Quantitating Radioactive Elements in Tissues

Abstract

Accurate quantitative microscopic studies of tissue and cellular distribution of radioactive elements which decay with emission of alpha particles may be made quite easily by the technics to be described. The essential points in the technic are (1) the use of finegrained silver-bromide emulsions with selective response to alpha radiation. 1 , 2 (2) the mounting of tissue sections permanently on the emulsion at the beginning of the exposure. (3) examination of such preparations at 400 diameters in dark-field illumination for determination of number of alpha particle tracks per unit area of emulsion, and (4) examination of such preparations at 1000-2000 diameters for determination of the precise cellular location of the radioelement by tracing straight tracks through the emulsion to their points of origin in the tissue.

The following technics have been evolved in the study of radium F (polonium) which decays with emission of alpha particles and very low intensity gamma rays. The polonium is administered in physiological saline buffered with NaHCO₃. Tissues are fixed in buffered neutral 4% aqueous HCHO for 48 hours. Bones are decalcified in 5% aqueous HCOOH. Tissue blocks are dehydrated in acetone, cleared in gasoline, embedded in paraffin in a vacuum oven and sectioned at 5 μ. The ribbons are floated off cold water onto the photographic emulsion (Eastman alpha particle plate No. 329,489). All manipulations of the undeveloped photographic plates are carried out in a room illuminated by the appropriate safelight. The preparation is dried quickly in a current of air and is placed in a light-tight container for the remainder of the exposure period. At the end of the exposure period the paraffin is removed by placing the plate in xylene for 5 minutes and the plate is dried in a current of air. The plate is developed in D-19, hardened in SB-4, and fixed in F-5 (Eastman Kodak formulae) at room temperature after which it is washed in filtered tap water for 2 hours. The plate may be stained immediately or dried and stored for staining later. The plate is stained in freshly prepared Weigert's acid-iron hematoxylin for 2 minutes, washed in tap water 5 minutes, dehydrated in 3 changes of acetone, cleared in 1:1 acetone-xylene and in 3 changes of xylene. A drop of xylene-clarite is placed on the tissue and the preparation is covered with a glass coverslip.