Image Characteristics Flashcards
What is radiographic density?
Darkening of the film due to interactions with x-radiation, the overall darkening of the film is radiographic density
What is the formula for optical density?
Log of initial density divided by the transmitted intensity
What is base plus fog?
Inherent density that manufacturers add to the base of a film to enhance viewing characteristics
What are the two subject factors that affect intensity?
Subject density and subject thickness. If both of these factors increase the initial intensity is lowered and the optical density increases
What are the three exposure factors that affect intensity?
Tube current, higher current increases optical density
Exposure time, more photons increases optical density
Tube voltage, increases the number of electrons that hit the target which in turn increases optical density
Out of the three exposure factors, which one does not change intensity?
Exposure time
What is the characteristic curve?
Plot of exposure on the x-axis vs. radiographic density on the y-axis.
Increasing exposure makes the radiograph lighter or darker?
Darker
What is film latitude?
The range of useful exposures
What is radiographic contrast?
The difference in densities between two adjacent areas
How does gray scale relate to contrast?
Narrower gray scale means higher contrast. The less shades of gray the higher the contrast
Which dentists prefer high contrast and why? Low contrast?
General dentists prefer high contrast or narrow grayscale because it is easier to see caries
Periodontists prefer low contrast because its better for seeing soft tissue lesions
What is subject contrast?
Inherent properties of the person being radiographed
What happens to image contrast with increasing tube voltage?
It decreases, increases the grayscale
How can you compensate for higher tube voltage?
Decrease exposure time or the tube current
