Image Analysis Ch 2.2 Flashcards Preview

Radiography Spring 2016 > Image Analysis Ch 2.2 > Flashcards

Flashcards in Image Analysis Ch 2.2 Deck (25):
1

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

Once a marker is added postprocessing

2

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

3

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

4

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

5

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

6

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

7

Be able to define dynamic range

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

8

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

9

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

10

What quantum noise is characterized by

Graininess or a random superimposed pattern on the image

11

Know what it means to adjust a window width

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

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

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

13

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

14

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

15

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

16

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

17

Know what a grid alignment artifact looks like with film screen

Demonstrates a loss in density where the grid lines are shown

18

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

19

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

20

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

21

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

22

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

23

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

24

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.

25

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

Do not cover up the original marker