Transcript Chapter 8 The Four Radiographic Qualities

Chapter 8
The Four
Radiographic
Qualities
Radiographic Qualities
 There
are four distinct qualities in a
radiograph that determines the overall
quality of the film.
 They are:
Detail
Density
Contrast
Distortion
Detail

Detail is the delineation or demarcation
that separates one structure, organ or
tissue from another. The size of the
focal spot plays a large part in the
amount of detail seen on film.
Penumbra is the blurring of the edges
of an object due to the size of the focal
spot.
Detail
 Primary
Factor:
 Detail is primarily controlled by
the size of the focal spot. The
larger the focal spot, the poorer
the detail; the smaller the focal
spot, the better the detail, again,
due to the penumbra effect.
Detail
 Secondary
Factors:
 FAD
 PFD
 Improper
Kv
 (High
Kv = Grey film)
 (Low Kv = Black/White film)
 FAD
and PFD are concerned with
distortion but the greater the
distortion, the poorer the detail.
Density (MAS)

Density (MAS) is responsible for the
blackening effect on your film and
refers to the amount of light that will
pass through the film when it is held
before a viewing box. The amount of
density is directly proportional to the
percentage of blacks and grays as
compared to whites.
Density (MAS)

The greater the percentage of blacks
and grays the greater the density of
your film. If the white areas are
excessive, density would be considered
minimal. Proper density suggests just
the right proportion of blacks, whites
and grays for the area being
radiographed. With proper density one
would expect to see all the areas of the
film adequately.
Density (MAS)
 Primary
Factor:
 Density is primarily controlled
by the milliampere-seconds.
The greater the MAS, the
greater the density; the lower
the MAS, the less dense the
film.
Density (MAS)

Secondary Factors:

Exposure of the film to scattered rays or light
Exposure of the film to fumes, heat or
moisture
Improper FAD. When the distance is changed
and MAS is not taken into account the
density will be incorrect.
Developing Mistakes
Improper KV.




Contrast (Kv)
 Contrast
(KV) refers to the
differences between the black,
white and gray shadows that might
be represented on a radiograph.
 Excessive contrast suggests that the
shadows will be black and white
and little gray (short scale
contrast).
Contrast (Kv)
 Minimal
contrast suggests that
the shadows will be mostly
gray with little black or white
areas (Long scale contrast).
With proper contrast there is
proper distribution of these
three shadows.
Contrast (Kv)
Main Factor:
 Contrast is primarily controlled by the
kilovoltage since it is the kilovoltage
which controls the penetrating power of
the x-ray beam, that is , what portions of
the film will be white, what portions gray,
what portions black. With black shadows
there has been complete penetration, with
gray shadows some penetration and with
white shadows no penetration.

Contrast (Kv)

The higher the KV, the lower the contrast
(less difference in adjacent densities); the
lower the KV, the higher the contrast.
Remember that higher the kV the more
Comptons scattering. This scatter, which
occurs at the higher energy levels, will be
strong enough to make its way onto the
film. This is why higher kV levels often
result in grayer film.
Contrast (Kv)








Less important factors that may effect contrast:
Exposure of film to scattered rays or light
Exposure of film to fumes, heat or moisture
Outdated film
Improper FAD or Improper MAS
Developing Mistakes
Film emulsion characteristics
Contrast is increased by the use of cassettes
rather than cardboard holders
Distortion
 Distortion
is the
misrepresentation of an
anatomical structure on a
radiograph. It cannot be
completely avoided, but it can
be minimized. To minimize
distortion, use a close PFD and
a long FAD.
Distortion
 Main
Factors:
 Distortion is primarily controlled
by the film-anode distance. The
greater the FAD, the less the
distortion; the shorter the FAD, the
greater the distortion.
 Another important factor is PFD.
Distortion
 Less
important factors that may effect
contrast
 Improper positioning
 Angulation of the x-ray beam.
 Focal spot size due to magnification