MEDICO-BIOLOGIC RESEARCH 



O 



Brightness: ^Magnitude of light passing only x-rays from 1 to 10 A are used. 



through the microradiograph. These wave lengths of white radiation may 



Resolution of details: The visualization of be obtained at 12 kv and less in the x-ray 



structures invisible with the unaided eye. tube with tungsten target according to the 



Resolving power: Ability of an instrument Duane-Hunt law: 



12,400 



(e.g., microscope), photoemulsion, x-rays, 



etc. to bring into view structures not seen ^o (A) = — r^ (approximateh) {2) 



with the unaided eye. 



o 



It is obvious that the resolving power of X-rays 1 A long are absorbed by all mi- 

 the microradiograph is closely connected crostructures containing a sufficient amount 

 with both contrast and sharpness (see fur- of an element occupying a high place in the 

 ther about the unsharpness due to "discon- atomic chart, e.g., by any tissvie containing 

 trasting efTect" of the magnification). calcium or by blood vessels containing x-ray 

 Microstructures may be only then vis- opaque media, artificially introduced. Eight 

 ualized in a microradiograph if they absorb kv which generate white x-rays with the 

 a certain amount of x-rays and the effective effective wave length 1.55 A appear to be 

 intensity of rays which passed through these the lowest tension which can resolve details 

 structures is sufficient to produce either a mentioned above with the necessary con- 

 visible contrast within the emulsion layer or trast and sharpness. Harder rays (at 20-30 

 a conspicuous fluorescence of the screen. All kv) produce a blacker image than necessary 

 these dependencies are well expressed in the and do not effectively show certain differ- 

 equation: ences in contrasts, e.g., those between cal- 

 /pr = /abs I reff cium-rich and calcium-poor elements. On the 



other hand, the effective intensity of x-rays 



The primary intensity comprises x-ray obtained at 3 kv and less may be too weak to 



factor, the absorbed intensity depends produce any differentiation. If we take for 



mostly upon the object factor and the effec- example again the calcium-rich tissue, it 



tive intensity produces the x-ray image. All should appear homogeneously white in an 



these factors will now be discussed in detail, ultra-soft microradiograph. 



X-ray Factor. X-rays may resolve in Lamarque (81-83) has already pointed out 



two ways: qualitative and geometrical. The that there is no essential difference between 



first is the direct x-ray resolution; it is con- a microphotograph and a microradiograph 



nected only with the quality of x-rays used, of tissues and cells low in absorbing x-rays. 



It will be discussed in this paragraph. The and this assumption is supported to some 



geometrical resolution is closely connected extent by the following experiment of Boha- 



with the divergency of x-rays. Some data on tirchuk (unpublished) : two plates of the 



this resolution will be found in this para- same thickness (about 1 mm) one of lead 



graph (focal spot size). Other data will be (A) and the other of aluminum (B) were 



in the next paragraphs on object and image, radiographed with x-rays of different pene- 



The direct resolving power of x-rays de- trative power (Fig. 2). It is obvious that in 



pends either upon their wave length, if rays the radiograph made with 6 kv x-rays (1) 



are monochromatic, or upon the length of there is no difference in contrasts between 



an effective wave, if rays are "white" or images of both plates; in other words these 



"continuous" (mixed). The diapason of wave- soft x-rays are alike to fight in their effect, 



lengths of soft and ultra soft x-rays (those The differentiation becomes visible at 9 kv, 



longer than 4.2 A) is quite large— from 0.5 but only at 20 kv (2) is it quite clear. Cer- 



to 100 A. However, in microradiography tainly there is no proved indication in the 



593 



