Transcript Ch. 5- Radiographic Quality

Radiographic Quality
Chapter 5
Radiographic quality
 Refers to how easily details can be
perceived on a radiograph.

Need to obtain as much diagnostic
information as possible about the internal
structures of the patient.
Quality depends on
 Radiographic Density
 Contrast
 Geometric Factors that affect detail
Radiographic Density
 Defined as the degree of blackness or
darkness on a radiograph.
 Black areas on a developed radiograph
are produced by deposits of metallic
silver in the film emulsion that result from
exposure to x-rays and their subsequent
processing.
Density continued ….
 X-rays make radiographic film black

Degree of blackness on a radiograph
depends on the amount of x-rays reaching
the film.
 Density is influenced by the quantity and
quality of the x-ray beam, as well as the
type and thickness of the tissue under
examination.
Factors Affecting Radiographic
Density.
 Greater radiographic density may be
produced by increasing:
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Total # of x-rays that reach the film
The penetrating power of the x-rays
The developing time
The temperature of the developer
Let’s Review
 mAs- number of x-rays leaving the x-ray
tube in a set period of time.
 When kVp increases, the penetrating
power increases as well. This means
more x-rays will reach the film causing a
darker radiograph.
Other Density Influences
 Thickness and type of tissue being
radiographed.

Increase in thickness, means that the
patient can absorb more x-rays which will
results in a lighter image.
 Large
animals absorb more x-rays, so less xrays reach the film, so the lighter the image.
To compensate, we increase the kVp.
Type of Tissue
 Type of tissue affects density as well.
Higher density tissues will cause less xrays to reach film, therefore have lighter
areas on the film at that place.
Gray film, lacks good density
Contrast
 Defined as visible difference between
two adjacent radiographic densities
 Is divided into
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Radiographic Contrast
Subject Contrast
Radiographic Contrast
 Density between two adjacent areas on a
radiograph.
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Many black and white areas means you have
contrast.
If a radiograph has many grays and a small density
difference between 2 adjacent areas, then it has
low contrast.
Need right amount of contrast. Not desirable to
have to high or too low of contrast. Need it to be
just right. Want grays, blacks and whites so eye
can easily see detail.
Contrast is influenced by:
 kVp level
 Subject contrast
 Scatter radiation
 Film type
 Film fog
Subject Contrast
 Defined as the difference in density and
mass between two adjacent anatomic
structures
 Depends on:
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Thickness of the anatomic part.
Density of the anatomic part.
Contrast Continued
 Bone will have more white on the film
than soft tissue.
Bone -> high contrast -> low kVp
Soft tissue -> low contrast -> high kVp
Exposure factors
 Poor contrast is due to inappropriate exposure
factors.
 mAs- affects contrast when too little or too
much is used.
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Primarily affects density so should not affect
contrast if proper kVp is used.
If mAs is insufficient, contrast is reduced because
overall density of the radiograph is reduced.
If quantity of x-rays reaching the film is too low, film
will be pale.
If too much mAs is applied, overall film will be
blacker but less effect on contrast.
How should mAs be adjusted?
Kilovoltage
 Affects both contrast and density
 Increase in kVp = Increase in
penetrating power.
 Increase in kVp = shorter wavelengths
are produced.
 As penetrating power increases, so does
scatter radiation. This can alter
radiographic contrast.
kVp
 If too low, will have gray and white
appearance and image will be
imperceptible.
 Will have low density because unable to
reach film.
 Causes difficulty in distinguishing
anatomic organs
Scatter Radiation
 Radiation that does not form an image
and is scattered in all directions.
 Contrast is decreased because
inappropriate areas of the film are being
exposed.
Sources of Scatter Radiation
 From the Patient
 Table
 Film Tray
Backscatter
 Backscatter- radiation arising from
sources behind the image plane that are
scattered back to the image.
 Avoid backscatter by limiting the size of
the x-ray beam so that the field does not
exceed the image receptor.
 Cassettes contain lead- foil backing to
prevent backscatter from reaching the
film.
Grids
 When thick body parts are being
radiographed, you want to minimize
scatter radiation, you do this by using a
grid.
 Grid- device placed between the patient
and the radiographic film designed to
absorb non-image forming x-rays.
 Composed of alternating strips of lead
and spacer material.
Grids Continued
 Spacer material usually consists of fiber,
alumininum, or plastic because they
have low x-ray absorption
 Grids may be
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Placed on top of the cassette.
Built into the cassette.
Placed under the table between the patient
and the cassette.
Grid Pattern
 Linear Grid- most table top machines are
equipped with a linear grid- Lead strips
parallel in their longitudinal axis.
 Crossed Grid- 2 superimposed linear
grids absorbs maximum amount of
scatter radiation
Grids continued
 Generally grids now are a part of the
cassette or the x-ray table.
 Potter Bucky Diaphragm- usually found
in large animal situations.
 Grids must be adequately cared for, can
not be dropped because will result in
permanent damage.
Radiographic Detail and
Definition
 Terms used to describe image
sharpness, clarity, distinctness, and
perceptibility.
 Lack of detail factors

1. Geometric unsharpness- loss of detail
due to geometric distortion
 Large
focal spot size
 Decreased SID
 Motion
 Screens and films
 2. Geometric Distortion and
Magnification- variation in size and
shape of anatomic structures due to their
position in relation to the x-ray source
and film.

Important to keep areas being
radiographed parallel to image receptor to
avoid distortion.
 Distortions
include: Magnification, elongation,
foreshortening.