Image Analysis Ch 2.2

Question 1

Know when an image is no longer considered a legal document in regards to the marker

Answer 1

Once a marker is added postprocessing

Question 2

Be able to describe how you can estimate how much automatic rescaling occurred on an image

Answer 2

Through the exposure indicator number as long as a histogram analysis error has not occurred

Question 3

Know what happens to an image when the image has resulted in an exposure indicator number that is lower than ideal

Answer 3

May require repeating because of the mottle image appearance

Question 4

Be able to describe what quantum noise is and how to fix it

Answer 4

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

Question 5

Know what happens when an exposure indicator number is higher then the ideal value

Answer 5

Typically do not require repeating because of image quality unless they are so high above the ideal number that the image demonstrates excessive grayscale

Question 6

Be able to describe what the difference is between high contrast resolution and low contrast resolution

Answer 6

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

Question 7

Be able to define dynamic range

Answer 7

The range of gray shades that the imaging system can display is referred to as the dynamic range

Question 8

Know what a higher dynamic range means for an image

Answer 8

The more gray shades that are available for the pixels to display resulting in better contrast resolution

Question 9

Be able to differentiate the difference in digital imaging from filmscreen systems in regards to dynamic range

Answer 9

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

Question 10

What quantum noise is characterized by

Answer 10

Graininess or a random superimposed pattern on the image

Question 11

Know what it means to adjust a window width

Answer 11

Allows the viewer to increase or decrease the contrast of the image

Question 12

Know why you shouldn’t adjust window with and then save it to PACS instead you should leave it as the raw image taken

Answer 12

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

Question 13

Know why double exposure results are different from digital to filmscreen

Answer 13

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

Question 14

Know what an anatomic artifact is

Answer 14

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

Question 15

Know what an external artifact is and give examples

Answer 15

Artifact found outside the patient’s body

example: earrings, necklaces, bra hooks monitoring lines gown snaps

Question 16

Know what an internal artifact is and give examples

Answer 16

Artifact found within the patient and cannot be removed and must be accepted
Examples- prosthesis, pacemaker, central venous catheter

Question 17

Know what a grid alignment artifact looks like with film screen

Answer 17

Demonstrates a loss in density where the grid lines are shown

Question 18

Know what a grid alignment artifact looks like with digital radiography

Answer 18

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

Question 19

Be able to describe aliasing/moire artifact

Answer 19

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

Question 20

Know how to eliminate a aliasing/moire grid artifact

Answer 20

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

Question 21

Know what a phantom image is

Answer 21

Artifacts in the CR that occur when the Imaging plate is not adequately erased before the next image is exposed on it

Question 22

Know how scatter and fog can produce phantom images

Answer 22

When the computed radiography IR is accidentally exposed to scatter radiation when left in the room during other exposures

Question 23

Know what happens when the back of an IR is exposed to the x-ray Source

Answer 23

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

Question 24

Be Able to describe what the two most common phosphor plate artifacts are

Answer 24

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.

Question 25

Know if you must add an annotation what must you be careful not to do

Answer 25

Do not cover up the original marker