RADIOAUTOGRAPHY 



302 



RADIOAUTOGRAPHY 



a ferrous sulfate solution. By using 

 a physical rather than a chemical de- 

 velopment, it is theoretically possible 

 to obtain developed grains ranging 

 from 10~V to 1m in diameter. This 

 method, however, is still in the experi- 

 mental stage and there are several 

 serious technical difficulties that must 

 be overcome before the method can be 

 used in biological research, e.g., expo- 

 sures for more than two days have not 

 been successful due to the great accumu- 

 lation of background fog. 



Quantitative Determinations. 



Quantitative results have been ob- 

 tained using 1) densitometric measure- 

 ments, 2) grain counts, and 3) track 

 counts. 



The measurement of photographic 

 densities using a photometer is satis- 

 factory for work at low magnifications. 

 The magnified radioautographic image 

 is projected onto a frosted glass, and 

 estimated as "densities" (which are 

 measured as the log of the intensity of 

 incident over transmitted light). This 

 method has been used by Dobyns, 

 B. M., Skanse, B., and Maloof, F. 

 (J. Clin. Endocrinol., 1949, 9, 1171- 

 1184) and by Axelrod, D. J. and Hamil- 

 ton, J. G. (Am. J. Path., 1947, 23, 389- 

 412). Much work remains to be done 

 before densities may be translated in- 

 to concentrations of radio-elements. 



The counting of photographic grains 

 in an area outlined by a micrometer 

 placed in the ocular is the most satis- 

 factory method to estimate densities. 

 It may be used with small or large speci- 

 mens. All the grains in the area of the 

 emulsion overlying a reactive zone may 

 be counted (Pelc) or only the grains at 

 definite levels are recorded. Results 

 have been obtained with the latter 

 method in this Department in collabo- 

 ration with N. Nadler and a good agree- 

 ment with theoretical calculations was 

 found. 



The results may be expressed in 

 several ways. The density or grain 

 counts in one structure may be com- 

 pared with that of another structure in 

 the same tissue or animal or they may 

 be expressed in more absolute terms by 

 comparison with densities or grain 

 counts of standards radioautographed 

 at the same time as the test material 

 and containing known amounts of 

 radioactivity and geometry (Dudley, 

 R. A., and Dobyns, B. M., Science, 

 1949, 109, 327-328; Nadler, N. J. and 

 Bogoroch, R., Anat. Rec, Supplement, 

 1951, 109, 69). 



When attempting quantitative com- 

 parisons, the geometry of the source, 

 the distance between source and emul- 



sion, i.e., interspace, the emulsion and 

 section thickness must all be taken into 

 consideration. It must also be re- 

 membered that the density remains 

 proportional to the intensity of the 

 source, and thus to the concentration 

 of the isotope, only when the exposure 

 is kept to a minimum. Otherwise the 

 relationship between density and con- 

 centration is more complex. 



It is necessary to have uniform emul- 

 sions of absolute thicknesses (such as 

 stripping films) for densitometric meas- 

 urements since all the grains in every 

 level of the emulsion are measured. 

 On the other hand, when only definite 

 levels in the emulsion are examined 

 for grain counts, small variations in 

 emulsion thickness are unimportant. 

 The liquid coating method has made 

 it possible to obtain reproducible 

 quantitative results under these condi- 

 tions. 



The counting of tracks per unit area 

 using nuclear emulsions for o and rays 

 may also be used as a quantitative 

 method (Boyd, G. A. and Levi, H., 

 Science, 1950, 111, 58-59). 



Qualitative Results. 



Space does not permit a review of 

 the interpretation of the many results 

 that have been obtained using the vari- 

 ous techniques described above. Such 

 a review with bibliography as previ- 

 ously mentioned has been given by 

 Gross et al. Only a few examples of 

 the more extensive work with this 

 technique will therefore be cited. 



Foreign substances such as heavy 

 metals or fission products have been 

 investigated radioautographically es- 

 pecially by the Berkeley group under 

 J. G. Hamilton. The actinide and 

 lanthanide groups of elements, adminis- 

 tered as their ions, are found to be 

 localized primarily in bone where they 

 remain for considerable periods of 

 time. The elements related to calcium 

 localize mostly in the growing ends of 

 bone. 



The dynamics of phosphate deposi- 

 tion were used to study the growth of 

 bone by Leblond, C. P., Wilkinson, 

 G. W., B^langer, L. F., and Robichon, 

 J., (Am. J. Anat., 1950, 86, 289-341). 

 By studying coated and inverted 

 radioautographs of serial sections of 

 bones obtained from young rats sacri- 

 ficed at various time intervals after in- 

 jection of P^'^, these authors found that 

 two types of reactions occurred soon 

 after injection, diffuse and localized. 

 The diffuse reaction, extending through- 

 out the bone, was due to exchange 

 between labeled circulating phosphates 

 and the surface phosphates of crystals 



