Week 9 - Artifacts Flashcards
Any irregularities on an image that is not caused by proper shadowing of tissue by the primary xray beam
Artifact
Artifacts can be characterized by their cause, what are some examples?
-processing
-handling
-software
-object
-operator
Artifacts that are greater in radiographic density than the surrounding area
Plus density artifact
Artifacts that are less radiographically dense than the surrounding area
Minus density artifacts
What are common causes of image receptor artifacts?
Rough handling
Scratches
Dust
Pixel malfunction
T/F
There is no such thing as “radiation fatigue” or IRs
-they should last for thousands of exposures
True
-irregular line patterns caused by noise in the plate reader electronics
-requires CR reader to be serviced
Noise artifacts
(A) an exposure of a correctly oriented grid with the grid lines perpendicular to the plate readers scan lines
(B) a moire pattern caused by an incorrectly oriented grid, with the plate readers scan lines
Moire effect
Radiograph demonstrating a CR reader light guide artifact
Reader artifacts
What are some examples of artifacts caused by operator error?
Improper collimation
-poor histogram analysis
-contrast differences
CR cassette upside down
-results in artifacts from hinges, etc. on the back of the cassette
Artifacts occurring because of incomplete erasure of a previous image on a CR IP
Ghost artifacts
-if a CR IP has not been used for 24 hours it should be erased again before use
T/F
Environmental radiation can contribute to ghost artifacts
True
What is an example of a time where interpolation would be used for artifacts?
Software artifacts
Ex. Dead pixel or dead row
The process of assigning a value to a dead pixel based on the recorded values of adjacent pixels
Interpolation
T/F
If an image is taken prior to the detector releasing all the signal from the previous image, a faint image of the previous exposure may be visible
True
Can be avoided by:
-increasing time between exposures
-collimating to reduce amount of unattenuated beam
-use appropriate technical factors
What is the appearance of the resultant image if the exposure field is not properly collimated, size and positioned?
This can lead to histogram analysis errors
The result is very dark or very light or very noisy images
What are some examples of object artifacts?
Jewelry, hair accessories, hearing aids….
What artifact is caused by involuntary, voluntary or equipment motion
Motion artifacts
Defined as a decrease in number of transmitted photons reaching IR due to misalignment of grid with divergence of beam
Grid cut off errors
-when a focused grid is placed upside down on the IR
-results in grid lines going opposite the angle of divergence
-loss of exposure to the edges as the Center has parallel line
Upside down focused
-xray beam angled across lead strips
-can be due to an angled tube or an angled grid
-results in overall decrease in exposure
-can occur with both focus and parallel grids
Off level
-“lateral decentering”
-central ray is not aligned side to side with focused grid; divergence doesn’t match angle of lead strips
-results in overall loss in density across image
Off center
-occurs when SID is outside the recommended focal range
-grid cutoff occurs if the SID is less than or greater than the focal range
-results in loss of exposure on the periphery of the images
Off focus
-refers to an insufficient number of incoming xray photons reaching the image receptor
-it is visible as brightness or density fluctuations on the image
Quantum mottle
*requires increase of incoming signal, by increasing mAs
-created by scatter exit radiation
Fog
*grids help absorb scatter radiation that exit the patient
