AUTOKADIOGRAPIIY OF TISSUE 



lowed it, and this in turn was followed by a 

 section stained by the Mallory method, to 

 register connective tissue locations in rela- 

 tion to the "spot diameter" regponse of the 

 unstained autoradiograms. A "spot diam- 

 eter" is the grain response of the emulsion 

 to a single radioactive particle. The staining 

 sequence was followed through the entire 

 lung. All of the sections were measured 

 for Ru^"^ content on a mica window beta 

 counter. 



The insoluble ruthenium particles elicited 

 a specific "spot diameter" response in the 

 NTB emulsion. This was a well defined cir- 

 cular area of developed emulsion grains over 

 the precise location of the deposited par- 

 ticles, as illustrated in Figure 7. 



Knowing the total activity density for a 

 specific slide, the activity density of a single 

 particle was taken as proportional to the 

 diameter of the darkened area of the emul- 

 sion. Thus, if a number of particles were 

 present on a single slide, the total counting 

 rate was compared with the sum of all of 

 the darkened areas on that slide. Therefore, 

 each particle could be assigned an activity 

 density evaluation directly proportional to 

 the size of the individual "spot diameter" 

 measurement of the emulsion. The "spot 

 diameter" darkenings of the grains of the 

 emulsion varied in size and ranged from 8 fj, 

 to 170 fjL. A quantitative straight -line func- 

 tion exists between the sum of the spot 

 diameters or a single-spot diameter and the 

 total activity of each autoradiogram. 



This particular technique provides a 

 means of measuring the radioactivity of a 

 single radioactive particle or many particles 

 within tissue when the exposure, processing 

 and development are standardized. The par- 

 ticles occur in a pattern of distribution such 

 that the accumulated dose from nearby par- 

 ticles is sufficient to initiate fibrosis. By 

 means of the serial sections stained specifi- 

 cally for connective tissue, and the autora- 

 diograms, it is possible to reconstruct the 

 tissue in depth and study the relationship 



^ 





4 



GRAIN DENSITY 



Fig. 7. Stained lung-autoradiogram prepara- 

 tion illustrating deposition of Rui^^Qa particles 

 with resultant spot diameter darkenings. (Courtesy 

 J. Biol. Phot. Assoc.^^). 



of the fibrosis to the specific location of the 

 deposited radioactive particles. 



The autoradiographic technique for 

 Sr^oS04 in lung tissue of mice, administered 

 1 /iC per animal by inhalation, is mentioned 

 here for comparison with the foregoing meth- 

 ods. 



Sections from lung tissue fixed in 80% 

 ethyl alcohol were processed in a manner 

 similar to lung tissue containing Ru*"^ par- 

 ticles (7). The film used in this case, how- 

 ever, was 25 n No-Screen x-ray, single coated 

 on 1 X 3 inch slides. These slides had a pro- 

 tective coating. As counting techniques indi- 

 cated a low activity densitj^ for the sections, 

 they were exposed for 8 weeks. The use of 

 X-ray emulsion made it possible to register 

 activity densities that were approaching the 

 lower limits of detection by normal counting 

 methods. 



The autoradiogram of the lung section 

 containing Sr^", illustrated in Figure 8, shows 

 both a diffuse and particulate response to 

 the radioactive material. The adjacent his- 



