MEDICO-BIOLOGIC RESEARCH 



with the same radiation at different angles 

 of incidence. Examples are given in the 

 literature (5). If microradiography by pro- 

 jection is employed diffraction can produce 

 images which correspond to a reduced inten- 

 sity of transmitted radiation and simulta- 

 neous images from intensity diffracted in 

 forward directions with Bragg angles less 

 than 45° (10). This effect is similar to the 

 phenomenon of diffraction from coarse grains 

 in metal specimens giving mottling effects 

 on macro radiographs (11). 



REFERENCES 



1. Sharpe, R. S., "X-Ray Microscopy and Mi- 



croradiography," pp. 591-602, Academic 

 Press, New York, 1957. (Edited by V. E. 

 Cosslett, A. Engstrom and H. H. Pattee, 

 Jr.) 



2. Johnson, W. and Andrews, K. W., Iron and 



Steel, 31, 437-444, 1958. 



3. Betteridge, W. and Sharpe, R. S., /. Iron 



and Steel Inst., 158, 185-191 (1948). 



4. This Encj'clopedia Section, p. 561, 574. 



5. Andrews, K. W. and Johnson, W., pp. 581- 



589 of Reference (1). 



6. MoRLEY, J. I., Iron and Steel hist. Spec. Report 



No. 43, pp. 195-205. (Esp. Figs. 48-51 and p. 

 200). 



7. KiRKY, H. W. AND MoRLEY, J. I., J. Iron and 



Steel Inst., 158, 289-294, 1948 (Esp. Figs. 

 34-40). 



8. Clark, G. L. and Gross, S. T., Ind. Eng. 



Chem. Anal. Ed. 14, 676-683 (1942). 



9. GoLDSCHMiDT, H. J., "Tlie Mechanism of 



Phase Transformations in Metals," pp. 

 105-119, 1956, The Institute of Metals, 

 London. (Monograph and Report series, 

 Xo. 18.) 



10. VoTAVA, E., Berghezan, a., and Gillette, 



R. H., pp. 603-616 of Reference (1). 



11. Glaisher, W. H., Betteridge, W., and 



Eborall, R., J. Inst. Met., 70, 81 (1944). 



K. W. Andrews 



W. JOHNSOX 



MEDICO-BIOLOGIC RESEARCH BY MICRO- 

 RADIOGRAPHY 



Theory and Technique 



Microradiography in medico-biological re- 

 search is that method by which a magnified 

 radiographic image (microradiograph) of an 



object is obtained. It is desirable to bring 

 the minimum magnification into this defi- 

 nition because there are many workers using 

 powers as low as 2X or 3X, claiming such 

 slightly enlarged radiographs to be micro- 

 radiographs. On the other hand, the power 

 may be called "micro" if it brings into view 

 such structures as cells, thin fibers, capil- 

 laries, etc., which are not seen with the un- 

 aided eye or with the low power mentioned 

 above. It is proposed to consider 35 X to be 

 this minimum power of a microradiograph. 



Magnification of an x-ray image may be 

 effected with different methods discussed in 

 several articles of this book. Most of these 

 are of recent proposition and are now in the 

 experimental stage; only contact microra- 

 diography has been used in medico-biologi- 

 cal research for more than 20 years (in rela- 

 tion to this research this method is 

 sometimes called "historadiography"). In 

 1951 Cosslett and Xixon proposed their 

 "x-ray shadow microscope", later termed 

 "x-ray projection microscope" for use in 

 medico-biological research. Theory and tech- 

 nique of the x-ray projection microscopy are 

 described elsewhere in this book and will 

 therefore not be discussed here. The method 

 attracts with its possibility of obtaining a 

 magnification of the radiographic image 

 without interference from emulsion graini- 

 ness. Principles of both methods are illus- 

 trated in Fig. 1. 



Before it can be indefinitely applied in 

 medico-biological research, however, the x- 

 ray projection microscopy has to work out 

 several problems of which the most impor- 

 tant is that of the resolution of microstruc- 



o 



tures with x-rays 1 A or longer. These rays 

 have a very low effective intensity especially 

 at the distance necessary for a magnified 

 image. This intensity is increased in the 

 contemporary x-ray projection microscopy 

 by making use of higher kilovoltage and, 

 consequently, harder x-rays. 



Literature data on the x-ray projection 

 microscopy show, however, that even these 



591 



