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Electronic Computers /3I :3 



The soft-tissue problem may be simplified somewhat by using mono- 

 chromatic X rays. In this case, the equivalent wedge thickness of the 

 soft tissue has some meaning. However, it is still necessary to guess the 

 thickness of the soft tissue over the bone. If two monochromatic X-ray 

 photographs are taken at different wavelengths, each with the same bone 



i 



Absorption 

 due to Soft 

 Tissue only 



Absorption 

 due to Soft 

 Tissue only 



Distance Across Trace Path 



Figure 2. A cross section through the 

 humerus. The upper figure shows the 

 bone and soft tissue distribution. The 

 lower figure shows the optical density 

 of the X-ray film. Based on original 

 data of H. Schraer. The 

 Pennsylvania State University. 



Distance Across Trace Path 



Figure 3. Equivalent wedge thick- 

 ness. This is for the same trace path 

 shown in Figure 2. The abscissa 

 (distance axis) is the same in both 

 figures. The ordinate scales have 

 been adjusted to make the peaks 

 coincide. 



and wedge on the picture, then it is possible to determine independently 

 the mass of both the bone and the soft tissue lying around it. 



A similar procedure has been employed using two wedges, one an 

 analog of the bone and the other an analog of the soft tissue. These 

 are placed in the path of two monochromatic X-ray beams of different 

 wavelengths which pass through the wedges, soft tissue, and bone to 

 scintillation counters. The limb is moved across the beam and the 

 wedges adjusted to give a constant intensity at both wavelengths at the 



