Operating Manual

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11.5 Summary of factors that influence image quality
The factors that influence image quality are:
1. Contrast
2. Unsharpness
3. Graininess
1 Contrast depends on:
• Radiation energy (hardness)
• Variation in thickness
• Backscatter
• Front- and back screen
• Film-screen combination
• Film-screen contact
• Defect location, depth as well as orientation
2 Unsharpness depends on:
• Size of focus
• Thickness of the object
• Source-to-film distance
• Radiation energy (hardness)
• Film-screen combination
• Film-screen contact
3 Graininess depends on:
• Type of film
• Type of screen
• Developing procedure
• Radiation energy (hardness)
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11.4 Radiation hardness and film contrast
When radiation hardness increases, the half-value thickness (HVT) also increases.
Tables 2-2 and 3-2 for steel and lead respectively show this in figures.
This is why in an object with different thicknesses, image contrast diminishes when radi-
ation hardness increases. Figure 7-11 clearly illustrates this.
The left side of a step-wedge is radiographed with 150 kV, the right side with 80 kV.
The right side shows the greater contrast between two steps, whereas on the left the
contrast range is the biggest.
Fig. 7-11. X-rays of a step-wedge with 150 kV (left) and 80 kV (right).
150 kV 80 kV