Transcript Film faults and factors affecting the radiographic

Factors affecting the radiographic
.
image and film faults
Image quality
I. Contrast
II. Image geometry
III. Characteristics of the X-ray beam
I. Contrast
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Subject contrast
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Film contrast
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Fog and scatter
Subject contrast
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Differences in tissue thickness
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Differences in tissue density
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kV or penetrating power of the radiation
beam
Film contrast
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The characteristic curve of the film
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Optical density
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Type of film- direct or indirect action
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Processing
Fog and scatter
Fogged film
Scatter radiation from within the patient’s
tissues
Perception of the radiographic
image
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Partial images-we all see the same partial
images but we don’t necessarily perceive
the same object
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Contrast
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Context
Effect of partial image
The effect of contrast
The effect of context
Image geometry
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Positioning of the film, object and x-ray
beam
Focal spot size and principle of line focus
Focal spot-object distance (FSOD), objectto film-distance (OFD)
Ideal image geometry
requirements
Focal spot size, heat distribution
and image sharpness
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Focal spot 1mm
Heat needs to be distributed over as large
as possible area
Principle of line focus
Focal spot-to filmdistance(FSFD)
FSFD
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Increasing the distance between the focal
spot and the object results in an image
with increased sharpness and less
magnification of the object
Object-to film- distance (OFD)
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Decreasing the distance between the
object and the film increases the
sharpness and result in less magnification
of the object
Image shape distortion
Cont’d
Practical factors influencing
image quality
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The X-ray equipment
The image receptor/screen combination
Processing
The patient
The operator and radiographic technique
Typical film faults
I.
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Film too dark
Overexposure
Overdevelopment
Fogging
Thin patients tissues
Films with inadequate
contrast
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Processing errors
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Exposure errors
Image unsharp and blurred
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Movement of the patient during the
exposure
Excessive bending of the film during
the exposure
Poor film/screen contact within the
cassette
Film marked
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Film packet bent by the operator
Careless handling of the film in the
darkroom :
Finger prints
Finger nails
Bending
Static electricity
Operator positioning faults
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1.Incorrect placement of the film packet
Back to front, image of the lead foil
evident
( film also too pale)
Inadvertently used twice, double exposure
(films also too dark)
Not covering the area of interest