Chapter 9 Flashcards
What determines the overall quality of an image?
Visibility of anatomic structures and the accuracy of their structural lines (sharpness)
Brightness and contrast are used to describe an images:
Visibility
How is image sharpness acheived?
Maximizing spatial resolution and minimizing distortion
How is visibility acheived?
Properly balancing brightness and contrast
What is brightness?
The amount of luminance of a display monitor
Brightness can easily be adjusted in digtial imaging because the images are formed by:
Numerical data
How is brightness adjusted in digital imaging?
Adjusting technique or adjusting window during post processing
Why should a radiographer repeat the image if it is way too dark or too bright?
Windowing can correct brightness but it cannot correct over or under penetrated
What does a receptor need to properly utilize as much of the remnant beam as possible?
Wide dynamic range
What should the radiographer evaluate before sending an image to PACS?
Proper exposure, not just brightness
What is saturation?
Receptor is over exposed, resulting in an image that is burnt out and cannot be corrected with windowing
What causes an image to look grainy?
Receptor is underexposed
What are exposure indicators?
Numeric values that indicate the amount of radiation exposure received
What is image contrast?
The exhibited difference in brightness levels within an image
What causes an image to have a washed out appearance?
Too little contrast
What causes an image to have a black and white appearance
High contrast
When do we want high contrast vs low contrast?
High - bony structures
Low - Soft tissue
What is radiographic contrast?
Combined results of dynamic range, radiation quality, and the characteristics of tissues being imaged
What is subject contrast?
Refers to the absorption characteristics of the tissues being imaged
What tissue characteristics affect contrast?
Thickness, density, and effective atomic number
How does high radiation quality alter subject contrast?
The stronger the beam, the more likely it is to scatter or pass through the body
Less chance of absorption results in fewer brightness differences - lower contrast
How does high absorption affect subject contrast?
More brightness differences in the image, but can also degrade image quality of IR is not properly exposed
Contrast is a complex image attribute, it is more _______ than brightness
Subjective