Factors Affecting Radiographic Quality
|Source to Image Distance (SID)|
|Object to Image Distance (OID)|
|Focal Spot Size|
|Cones & Collimators|
|Generator Power Source|
“diagnostic” radiograph is defined as one showing the tissues adequately
penetrated, sharply outlined, and the variations in tissue opacity sufficiently
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.
deposit of silver
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
of silver Controlling
quantity of radiation, grid, cone, intensifying screens, direct exposure, filter
processing, secondary radiation fog.
and visibility of image
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
of details--Magnification—change in size
distortion-change in shape
factors—Source to object
to film alignment
contrast and detail are photographic aspects of radiographic quality.
Detail and distortion are geometric aspects of radiographic quality.
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.
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
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.