RADIOGRAPHY 825 



the technician or doctor in charge of the X-ray department may find that some other 

 combination of factors produces a radiograph more to their liking. The operative- 

 technique chart with accompanying remarks shows the procedure for one particular 

 model X-ray unit and tube. 



A rough beginning for techniques with other apparatus may be obtained from this 

 chart (Table I) as follows: Take the product of current (milliamperes, ma.) multiplied 

 by the time, which will give milliampere-seconds, and then adhere to the other factors 

 shown. For instance, in this chart, radiography of the gall bladder calls for 60 ma. at 

 56 kilovolts for 2 sec. at 30 in. distance. If it is desired to make this radiograph with 

 an outfit that will not run so high as 60 ma. for 2 sec, the first step is to determine 

 the current-time factor, which in this case is 60 times 2, or 120 ma.-sec. If another 

 machine will operate at 30 ma. for 4 sec. at 56 kilovolts, the resulting film should be 

 about the same using a 30-in. distance. In any event, use of similar total milliampere- 

 seconds, with other factors as shown, will serve as a starting point for development of a 

 satisfactory technique. 



Exposure times for areas subject to movement should be as short as possible. A 

 heart which completes its diastole and systole 80 times a minute performs one of these 

 functions in about 0.3 sec. Therefore, to avoid blurring, a heart picture must be taken 

 in as small a fraction of a second as possible. Also to be considered is the fact that 

 each heart beat displaces various surrounding tissues, e.g., the lung. 



Clinical Interpretation. — Correct interpretation of clinical radiographs depends 

 almost entirely on experience under some efficient diagnostician. No amount of 

 study can take the place of actual viewing of films. Film diagnosis is not part of an 

 X-ray technician's work and under no condition should the technician attempt to give 

 such information to a patient without the consent of the radiologist in charge. Infrac- 

 tion of this rule may lead to serious consequences. 



Industrial Radiography, — While the application of X rays in industry for deter- 

 mination of flaws and internal defects in industrial materials is a more recent develop- 

 ment than that of medical radiographic diagnosis, it has progressed so rapidly in the 

 past few years that the value of this inspection method is no longer questioned. 

 Industrial radiography is the only nondestructive test now known for the actual 

 visualization of subsurface conditions. X-ray examination of welds, castings, molds, 

 radio tubes, and countless other manufactured articles is now a routine occurrence in 

 numerous plants throughout the world. As in medicine, the basis of industrial 

 radiography is the differential absorption of X rays by matter of varying densities. In 

 radiography of an object containing areas which, intentionally or not, differ in density 

 from surrounding material, those areas will register on a film providing they are not too 

 small. In general, defects IH to 2 per cent of the total thickness of the object under 

 inspection can be detected, and in special instances flaws as small as 1 per cent can be 

 demonstrated. If, for example, in a sample of carbon steel the carbon has precipitated 

 in one section, that area will be of lower density than the surrounding steel and allow 

 X rays to pass more freely. The result will be a dark spot on the film signifying 

 increased exposure. Any section of increased density will absorb X rays more readily 

 and record a lighter area on the film. When handled correctly, areas of increased 

 and decreased density may be registered on a film in faithful reproduction of the 

 original as to size and shape. Ordinary radiographic technique does not magnify or 

 enlarge any objects or their defects on the final film. 



Industrial X-ray Apparatus. — Industrial X-ray apparatus operates on the same 

 principle as medical radiographic machines, but whereas clinical equipment only 

 occasionally exceeds a rating of 100,000 volts, industrial work often requires a 200,000- 

 volt technique and in some instances industrial apparatus can be run as high as 400000, 

 volts. 



