X-RAY MICROSCOPY 



FILM — _ 



SPECIMEN 



X-RAY 



TUBE 



CMR PMR 



Fig. 1. Scheme of contact microradiography 

 (CMR) and projection microradiography (PMR). 

 Dependence is shown in P.M.R. of magnification 

 upon the distance: specimen — film. 



hard projection micrographs (at 20-30 kv) 

 are made at comparatively short distance be- 

 cause their maximum true magnification 

 (not that achieved by the following photo- 

 graphic enlargement) is shown to be about 

 30 X. This is much lower than the working 

 magnification of contact microradiography 

 (around 120-150X). However, this difficulty 

 of PMR may be overcome through making 

 use of ultra-sensitive emulsions and by carry- 

 ing out microradiography in vacuum. To our 

 knowledge these experiments are now in 

 progress. There are some reasons to beheve 

 that they will be successful and the x-ray 

 projection microscopy may soon be widely 

 used in medico-biological research together 

 with contact microradiography. 



Microradiography can take its place in 

 medico-biological research equally with other 

 methods if it complies with the following 

 requirements : 



A. If it presents an image of details with 

 satisfactory contrasts and sharpness which 

 reduce the error to an admissible minimum. 



B. If a possibility exists of increasing x-ray 



absorption artificially via selective x-ray 

 coloring. 



C. If there is a facility of comparing 

 microradiographical patterns of details with 

 those obtained by other methods of micro- 

 scopical anatomy. 



It will be shown that all these require- 

 ments are fulfilled in microradiography. 



Contrast and Sharpness in Microra- 

 diography (Terminology relevant to mi- 

 croradiography used in this article, mostly 

 after Bronkhorst (37). 



Contrast: The amount of precipitated silver 

 in the emulsion layer of a radiographed 

 and processed film or plate which can be 

 measured in units of blackness. Color of 

 black velvet comprises approximately 2.0 

 of these units, color of a sheet of white 

 paper — zero units, with all transitions 

 from black to white having a definite 

 numerical expression in these units. 

 Difference in contrasts: Difference between 

 two contrasts of any present in a micro- 

 radiograph. 

 Range of contrasts: The number of contrasts 

 present in a microradiograph. Microra- 

 diograph is poor in contrasts if their range 

 is within the limits 20-30; 100 and more 

 is the range of a microradiograph rich in 

 contrasts. 

 Density: Transparency of a given microra- 

 diograph or part of it to the passing light. 

 Sharpness (definition or detail): The exact- 

 ness in picturing of details. One point of 

 the image corresponds to one point of the 

 object in an ideally sharp microradio- 

 graph. 

 Marginal sharpness: Sharpness seen on mar- 

 gins of the image of a microstructure. 

 Depth sharpness: Sharpness of image of mi- 

 crostructures which are far from the emul- 

 sion layer during microradiography. 

 Unsharpness: Inexactness in picturing of de- 

 tails. It is revealed as blurring either of 

 margins or of structural details of the im- 



age. 



592 



