CH 27 Contrast & CH18Grids

Question 1

Visibilty of detail

Answer 1

Image is visible to the human eye only because contrast permits it.

Question 2

Image contrast

Answer 2

difference between adjacent densities/IR exposures

Question 3

Subject contrast

Answer 3

in patient, differential absorption differences in densities.

Question 4

Window width

Answer 4

Manipulating the contrast on digital systems

Question 5

Contrasts main controlling factor?

Answer 5

kV

Question 6

Larger differences between densities means

Answer 6

High contrast (less gray)

Question 7

In regards to contrast what happens when kV decreases?

Answer 7

Contrast increases/High Contrast

Question 8

High contrast means that the image has?

Answer 8

less densities, shorter scale

Question 9

In regards to contrast what happens when kV increases?

Answer 9

Contrast decreases/Low contrast

Question 10

Low contrast means the image has?

Answer 10

More denities, scale is longer

Question 11

In regard to bone work what would kV be?

Answer 11

Lower to moderate kV.

Question 12

Short scale is the same as?

Answer 12

High Contrast

Question 13

Long scale is the same as?

Answer 13

Low contrast

Question 14

In regards to soft tissue what would kV be?

Answer 14

Higher kV

Question 15

Subject contrast

Answer 15

dependent on the amount of kV, type of tissue and tissue thickness

Question 16

Use of a grid leads to

Answer 16

higher contrast, removes sctter, less densities, shorter scale, higher contrast

Question 17

An increase of ___% (____kv) at 30-50kV will lead to a visible change?

Answer 17

4-5%, 1-3

Question 18

An increase of ___% (____kv) at 50-90kV will lead to a visible change?

Answer 18

8-9%,4-8

Question 19

An increase of ___% (___kv) at 90-130kV will lead to a visible change?

Answer 19

10-12%, 9-16kv

Question 20

15 percent rule

Answer 20

Increasing kV by 15% will increase the density 2xs. Decreasing it by 15% will cut denisty in half.

Question 21

Film base is made of

Answer 21

polyester that pocesses an inherent blue dye and fog.

Question 22

Latitude is

Answer 22

The range of densities that can be viewed on the radiograph.

Question 23

The geometric factors for detail are?

Answer 23

FSS (Focal Spot Size), SID (Source to IR Distance) and OID (Object to IR Distance).

Question 24

What kinds of screens are there? (In order from slowest to fastest)

Answer 24

1)Nonscreen, 2)Slow/Detail/Extremity 3)Medium/Par 4)Fast/High speed

Question 25

In order to help reduce motion, one should:

Answer 25

Use a faster exposure time/decrease in time.

Question 26

Voluntary movements are reduced by:

Answer 26

clear instructions and communication

Question 27

Involuntary movements causes:

Answer 27

Heartbeat, spasm, tremors, peristolces.

Question 28

Mechanical movement is caused by:

Answer 28

x-ray tube/locks, bucky

Question 29

Immobilization devices are

Answer 29

tape, sponges, sand bags, pigg o stat, mummy wrap

Question 30

Penumbra formula:

Answer 30

(Focal Spot Size X OID)/SOD

Question 31

What two types of distortion are there?

Answer 31

Size and Shape

Question 32

Elongation is caused by?

Answer 32

Incorrect angle of IR (Excessive)

Question 33

Foreshortening iss caused by

Answer 33

Angled part, or not sufficiently angled

Question 34

When should a grid be used?

Answer 34

When greater contrast is needed.

Question 35

The spaces between grid lines are

Answer 35

Radiolumenescent.

Question 36

The grid lines are considered:

Answer 36

Radiopaque

Question 37

What is the Moire Effect?

Answer 37

Grid error that occurs with Digital IR systems when the grid lines are captured and scanned parallel to the scan lines in the imaging plate reader.

Question 38

What type of grid has lead strips running in only one direction?

Answer 38

Parallel grid

Question 39

How is the focused grid designed?

Answer 39

It is designed to match the diverence of x-ray beam. So torward the middle the lines are parallel, however the outlines are more incline/slanted.

Question 40

How does the air gap technique improve contrast?

Answer 40

It increases OID, which in turn helps reduce scatter. The same amount of scatter will be created but less of it will reach the IR.

Question 41

The amount of scatter radiation increases with?

Answer 41

1)^Patient thickness 2) larger field sizes 3) Decrease in atomic number of the tissue