Image Analysis Ch 2.2 Flashcards
Know when an image is no longer considered a legal document in regards to the marker
Once a marker is added postprocessing
Be able to describe how you can estimate how much automatic rescaling occurred on an image
Through the exposure indicator number as long as a histogram analysis error has not occurred
Know what happens to an image when the image has resulted in an exposure indicator number that is lower than ideal
May require repeating because of the mottle image appearance
Be able to describe what quantum noise is and how to fix it
The blotchy appearance on the image that results when an insufficient number of photons reach the imaging plate
-to fix it an increase in exposure factors is needed to reduce the effects of quantum noise
Know what happens when an exposure indicator number is higher then the ideal value
Typically do not require repeating because of image quality unless they are so high above the ideal number that the image demonstrates excessive grayscale
Be able to describe what the difference is between high contrast resolution and low contrast resolution
The higher the contrast resolution the more distinct are the Adjacent structures of similar subject contrast.
the lower the contrast resolution the lower the shade differences
Be able to define dynamic range
The range of gray shades that the imaging system can display is referred to as the dynamic range
Know what a higher dynamic range means for an image
The more gray shades that are available for the pixels to display resulting in better contrast resolution
Be able to differentiate the difference in digital imaging from filmscreen systems in regards to dynamic range
Digital radiography systems have a 14 bit dynamic range allowing 16,384 shades of gray to be demonstrated this is superior to filmscreen systems that represent a dynamic range of only 1000 shades of gray
What quantum noise is characterized by
Graininess or a random superimposed pattern on the image
Know what it means to adjust a window width
Allows the viewer to increase or decrease the contrast of the image
Know why you shouldn’t adjust window with and then save it to PACS instead you should leave it as the raw image taken
Once the windowing has been done and the image is saved the Wide dynamic range from the original image is lost leaving only the range that was saved
Know why double exposure results are different from digital to filmscreen
When digital radiography is used a double exposed image will not demonstrate low brightness (a.k.a. high density) as with filmscreen because the image will be normalized during processing
Know what an anatomic artifact is
Any anatomic structure is within the image that could have been removed. includes super imposition over VOI and anatomy not supposed to be In image
Know what an external artifact is and give examples
Artifact found outside the patient’s body
example: earrings, necklaces, bra hooks monitoring lines gown snaps
Know what an internal artifact is and give examples
Artifact found within the patient and cannot be removed and must be accepted
Examples- prosthesis, pacemaker, central venous catheter
Know what a grid alignment artifact looks like with film screen
Demonstrates a loss in density where the grid lines are shown
Know what a grid alignment artifact looks like with digital radiography
Will show the grid lines, but will not demonstrate an increase in brightness value where the grid lines are visible because the image will be automatically rescaled to correct brightness as long as there is a grid cut off across the entire image
Be able to describe aliasing/moire artifact
Occurs when a stationary grid is used and the IR is placed in the reader so that the grids. Lead strips are aligned parallel with the scanning direction resulting in a wavy line pattern on the image it is more common with grids that have a frequency below 60 lines/cm
Know how to eliminate a aliasing/moire grid artifact
By using a moving grid to blur lines and a grid frequency of 60 lines per centimeter or higher and by processing the image so that the grids lead strips are aligned perpendicular to the plates reader laser scanning direction
Know what a phantom image is
Artifacts in the CR that occur when the Imaging plate is not adequately erased before the next image is exposed on it
Know how scatter and fog can produce phantom images
When the computed radiography IR is accidentally exposed to scatter radiation when left in the room during other exposures
Know what happens when the back of an IR is exposed to the x-ray Source
A faint white grid type, honeycomb or square pattern will be overlaying the image – there will also be white areas that correspond to the hinges if they are included within the exposure field
Be Able to describe what the two most common phosphor plate artifacts are
Dust or dirt particles and scratches on the surface of the phosphor plate produces small white dots or curved white lines. Dust or dirt artifacts can be corrected by cleaning the screen. Scratches are permanent unless you replace the plate.
Know if you must add an annotation what must you be careful not to do
Do not cover up the original marker
