Factors Affecting Radiographic Quality

FACTOR Density Contrast Sharpness Magnification Distortion
KV Kilovoltage      
mA milliamperage        
Time (Phototiming)        
Source to Image Distance (SID)  
Object to Image Distance (OID)    
Alignment        
Focal Spot Size        
Grid      
Cones & Collimators      
Filter      
Compression        
Contrast Media-dye      
Intensifying Screens      
Film    
Processing    
Motion        
Subject (Patient)      
Heel Effect        
Generator Power Source      

Radiographic Quality

 A “diagnostic” radiograph is defined as one showing the tissues adequately penetrated, sharply outlined, and the variations in tissue opacity sufficiently demonstrated.   There are two factors in radiographic quality control, namely the photographic effect and the geometric effect.  In the category of the photographic effect we find the following resultant factors of the four basic technical factors of mAS, Kv, and SID.

 Density- deposit of silver  Controlling factors—Ma, Time

Influencing factors-KvP, target-film distance, processing, air in tissue, tissue thickness, tissue opacity, film-intensifying screens, focal spot damage, filtration in the x-ray tube, added filters, usage of cones, stray radiation, the secondary radiation, stereo shift.

 

Contrast—presence of silver  Controlling factor—KvP

Influencing factors—Quality and quantity of radiation, grid, cone, intensifying screens, direct exposure, filter processing, secondary radiation fog.

 

Detail—presence and visibility of image

Influencing factors—proper density, proper contrast, focal spot size, anode angle and effective focal size, Source-object distance, Object-film distance, motion screen-film contact, intensifying screens, and type of screens

 

Distortion—accuracy of details--Magnification—change in size

Influencing factors—SID, OID

 

True distortion-change in shape

Influencing factors—Source to object to film alignment

 

Density, contrast and detail are photographic aspects of radiographic quality.  Detail and distortion are geometric aspects of radiographic quality.  There is a variation in the intensity due to the angle at which the x-rays are emitted from the focal spot of the tube.  This is called the “heel effect”.  This so called “heel effect” is the variation in intensity of the x-ray output with the angle of the x-ray emission from the focal spot.  The intensity of the beam diminishes fairly rapidly from the central-ray toward the anode side and increases slightly toward the cathode side.  This phenomenon can be made good use of in obtaining balanced densities in radiographs of heavier parts of the body.  To do so the patient is arranged relative to the tube so that the long axis of the tube is parallel to that of the boy part, with the anode toward the more easily penetrated area.  The “heel effect” is less noticeable in closed coned projections where the x-ray beam is fairly restricted.  But where there is larger collimation, it is very important.

 

Relative to radiographic contrast, which is defined as the differences in densities in the radiographic image as determined by the object tissue, there are basically two types.  The short scale, high contrast or low latitude radiograph demonstrates sharp definition of black, gray and white caused by low KvP’s short wave lengths.  Long scale, low contrast or high latitude radiographs show a blending of black, gray, and white caused by the high KvP’s short wave lengths.  Types of developer also demonstrate types of contrast.  Regular developer normally used at 68 degrees Fahrenheit for 5 minutes will demonstrate long scale contrast.  Rapid developer normally used at 68 degrees for 3 minutes would demonstrate short scale contrast.  Screen film demonstrates long scale contrast, just as light tissue will demonstrate short scale contrast.

 

Also of importance relative to the density factors of a resultant radiograph is the respiration effect.  Inspiration as compared to expiration requires an increase of one-third mAs for the same likeness or chest measurement.  Heart measurement effect, is controlled by the inspiration phase on a chest radiograph.  Another density factor which is utilized in special techniques is relative to the compensating filtration effect as determined by the usage of graduated aluminum filters, barium clay, and cast plaster wedges. 

 

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