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Questions and Answers
What is the ability to differentiate a structure that varies only slightly in density from its surroundings?
What is the ability to differentiate a structure that varies only slightly in density from its surroundings?
- Artifact detection
- Low-contrast sensitivity (correct)
- Image resolution
- High-contrast sensitivity
What is the term for any systematic discrepancy between the CT numbers in the reconstructed image and the true attenuation coefficients of the object?
What is the term for any systematic discrepancy between the CT numbers in the reconstructed image and the true attenuation coefficients of the object?
- Artifact (correct)
- Noise
- Beam hardening
- Image distortion
What is the cause of quantum mottle?
What is the cause of quantum mottle?
- Excessive number of x-ray photons detected
- Insufficient number of x-ray photons detected (correct)
- Inadequate image processing
- Malfunction of the X-ray tube
What is the result of decreasing the number of x-ray photons to create an image?
What is the result of decreasing the number of x-ray photons to create an image?
What type of artifact is caused by a temporary short circuit in the X-ray tube?
What type of artifact is caused by a temporary short circuit in the X-ray tube?
What is the term for the undesirable fluctuation of pixel values in an image of a homogeneous material?
What is the term for the undesirable fluctuation of pixel values in an image of a homogeneous material?
What is the result of increasing the signal-to-noise ratio?
What is the result of increasing the signal-to-noise ratio?
What type of artifact is also known as incomplete projection artifact?
What type of artifact is also known as incomplete projection artifact?
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Study Notes
Contrast Resolution
- Ability to differentiate structures that vary slightly in density from their surroundings
- Also referred to as sensitivity of the system or low-contrast sensitivity
- Encompasses low-contrast detectability, which is the ability to distinguish an object nearly the same density as its background
CT Image Artifacts
- Defined as anything appearing on the image that is not present in the object scanned
- Systematic discrepancy between reconstructed image CT numbers and true attenuation coefficients of the object
- Divided into three categories
Noise
- Undesirable fluctuation of pixel values in an image of a homogeneous material
- Recognized as grainy appearance or "Salt and pepper" look on an underexposed image
- Can occur due to quantum mottle, which results from insufficient detected photons
- Signal-to-noise ratio (SNR) measures the number of x-ray photons detected per pixel
- Higher SNR indicates less obtrusive background noise
Other Artifacts
- Out of field artifacts (also known as incomplete projection artifact)
- Tube arcing artifacts caused by temporary short circuit in the X-ray tube, leading to momentary loss of X-ray output
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