Radiographic Imaging Chapter 5 - Fauber

Front 1

Scatter is Primarily the Result of?

Back 1

Compton effect

Front 2

What factors affect the Amount and Energy of Scatter?

Back 2

kVp and tissue volume

Front 3

What are the effects of Increased kVp on photoelectric effect, penetration and Compton effect?

Back 3

increased x-ray transmission

reduced photoelectric interactions

increased Compton effect

Front 4

What are the purposes of Beam Restriction?

Back 4

limits patient exposure

reduces scatter

Front 5

What is the effect of a Beam Restricting Device?

Back 5

changes shape and size of primary beam

Front 6

What are the effects of Collimation on scatter, contrast and exposure technique?

Back 6

decreased scatter

increased contrast

may require increased exposure techniques of 30-50%

Front 7

What materials are used to Construct Collumators?

Back 7

metals that readily absorb x-rays

Front 8

Descript an Aperture Diaphragm.

Back 8

flat piece of lead that has a hole (aperture) in it

causes large areas of unsharpness on perimeter of radiograph

Front 9

Describe the Structures of Cones and Cylinders

Back 9

aperature diaphragm with extended flange

flange can also be telescoping

Front 10

What are the advantages of Cones and Cylinders?

Back 10

reduce unsharpness (cylinders are better)

Front 11

What is the Effect of the Angle of the Flange of the Cone?

Back 11

if cone angle is too great it then only acts as an aperture diaphragm

Front 12

Describe the construction and features of a Collimator.

Back 12

has multiple lead shutters which allow adjustment in the projected fields

has white light source and mirror to project light field onto the patient,indicating where primary beam will be projected

may also have cross hairs

Front 13

What is an Automatic Collimator?

Back 13

also called a positive beam-limiting device
automatically limits size and shape of beam to match IR
have override mechanism if needed

Front 14

Describe the features of a Grid and its effect on exposure. When should grids be used?

Back 14

device with thin lead strips with radiolucent interspaces used to absorb scatter

using a grid requires additional mAs

usually used whtn anatomic part is greater than 10 cm

Front 15

What effect does a Grid have on Contrast?

Back 15

increases contrast

Front 16

What are the characteristics and purpose of Interspace Material on a grid?

Back 16

radiolucent material that separates lead strips

Front 17

What is Grid Frequency?

Back 17

expresses number of lead lines per unit length

Ex: 30 lines/cm

Front 18

What is the Grid Ratio and how is it calculated

Back 18

height of lead strips divided by distance between strips

Grid Ratio = h/D

ratios usually range between 4 to 16:1

Front 19

What is the effect of High Grid Ratio grids?

Back 19

Increase contrast

Front 20

What type of Grid Patterns are available

Back 20

linear and cross-hatched

Front 21

Advantages/Disadvantages of Cross-Hatched Grids

Back 21

remove more scatter

x-ray tube cannot be angled

Front 22

What types of Grid Focus are available?

Back 22

parallel (nonfocused)

angled (focused)

Front 23

What is meant by the Convergent Point?

Back 23

point of x-ray origin from tube

Front 24

What is meant by the Convergent Line of a grid

Back 24

points connected alont the length of the grid

Front 25

What is Focal Distance (grid radius) of a grid?

Back 25

distance between the grid and the convergent point

Front 26

What is the Focal Range of a grid?

Back 26

recommended range of the SID that can be used with a focused grid

Ex: 36-42 inches

Front 27

Where is a Wafer Grid placed?

Back 27

matches the size of the cassette and is taped to the top of the IR

Front 28

What is a Grid Cassette?

Back 28

IR with grid permanently mounted to front surface

Front 29

What is a Grid Cap?

Back 29

a permanently mounted grid that allows IR to be mounted behind it

Front 30

What are Stationary Grids? What are their disadvantages?

Back 30

possible to see grid lines on the image

Front 31

What are Reciprocating Grids? What are their advantages?

Back 31

makes grid lines less visible

Front 32

What is the Potter-Bucky Diaphragm?

Back 32

a reciprocating grid located just above tray holding the IR

Front 33

What is a Long-Dimension Grid?

Back 33

has lead strips running parallel to the long axis of the grid

Front 34

What is a Short-Axis Grid?

Back 34

has lead strips running perpendicular to the long axis of the grid

used where it is difficult to center the central ray along the long axis

Front 35

Grid Conversion Factor (Bucky Factor)

Back 35

used to determine the adjustment in mAs needed when using a grid

GCF = mAs (with grid) / mAs (without grid)

a function of the grid ratio

Front 36

What formula is used when calculating exposure when using different grid factors?

Back 36

mAs1 GCF1
____ = ____

mAs2 GCF2

Front 37

What is Grid Cutoff and what causes grid cutoff?

Back 37

decreased number of transmitted photons reaching the IR because of grid misalignment

Front 38

What are the 4 Types of Grid Cutoff?

Back 38

1) upside-down focused grid - both sides of image very underexposed
2) off-level grid (tilted) - appears as exposure loss
3) off-center grid - one side of image underexposed
4) off-focus grid - both sides of image underexposed

Front 39

What is Moire Effect? What causes the Moire Effect?

Back 39

a zebra-pattern created when a stationary grid is used during computed imaging

results from the grid frequency being similar to the laser scanning frequency during image processing

Front 40

What is Air Gap Technique? What can be done to decrease magnification?

Back 40

scatter is reuced with an increased OID

requires increased SID to increase sharpness

Front 41

What are the characteristics of the typical grid?

Back 41

Linear (not crossed)

Focused (not parallel)

Mid-ratio (8:1 to 12:1)

Has a focal range of 40 - 72"

Front 42

The projected shape of the unrestricted primary beam is:

A) square

B) rectangular

C) circular

D) elliptical

Back 42

C

Front 43

A purpose of beam-restricting devices is to __________ by changing the size and shape of the primary beam.

A) increase patient dose

B) decrease scatter

C) increase IR exposure

D) decrease image contrase

Back 43

B

Front 44

The most effective type of beam-restricting device is the:

A) cone

B) aperture diaphragm

C) cylinder

D) collimater

Back 44

D

Front 45

Of the beam-restricting devices, which two are most similar:

A) cone & aperture diaphragm

B) cone and cylinder

C) aperture diaphragm & cylinder

D) aperture diaphragm & collimator

Back 45

B

Front 46

The purpose of automated collimation is to ensure that:

A) the quantity of scatter production is minimal

B) the field size does not exceed the IR size

C) maximal recorded detail and contrast are achieved

D) exposure to the IR is maintained

Back 46

B

Front 47

When making a significant increase in collimation,:

A) mAs should be increased

B) kVp should be increased

C) mAs should be decreased

D) mAs should be increased

Back 47

A

Front 48

Which of the following increases as collimation increases?

A) Patient exposure

B) Scatter production

C) Fog

D) Contrast

Back 48

D

Front 49

Which of the following statements is true of positive beam-limiting devices?

A) They are required on all radiographic installations

B) They are required on all new radiographic installations

C) They have never been required on radiographic installations

D) They were once required on new radiographic installations

Back 49

D

Front 50

The purpose of a grid in radiography is to:

A) increase IR exposure

B) increase image contrast

C) decrease patient dose

D) increase recorded detail

Back 50

B

Front 51

Grid ration is defined at the ratio of the:

A) height of the lead strips to the distance between them

B) width of the lead strips to their height

C) number of lead strips to their width

D) width of the lead strips to the width of the interspace material

Back 51

A

Front 52

As compared to parallel grids, focused grids:

A) have a greater grid frequency and lead content

B) can be used with either side facing the tube

C) have a wider range of grid ratios and frequencies

D) allow more x-ray photons to reach the image receptor

Back 52

D

Front 53

If 15 mAs is used to produce a particular level of exposure to the IR without a grid, what mAs would be needed to produce that same level of exposure using a 16:1 grid?

Back 53

90

Front 54

Grid cutoff, regardless of the cause, is most recognizable on a radiograph as reduced:

A) contrast

B) recorded detail

C) density

D) positioning

Back 54

C

Front 55

Off-focus grid cutoff occurs by using an SID that is not:

A) within the focal range of the grid

B) equal to the focal distance of the grid

C) at the level of the convergent line of the grid

D) at the level of the convergent point of the grid

Back 55

A

Front 56

The type of motion most used for moving grids is:

A) longitudinal

B) reciprocating

C) circular

D) esingle stroke

Back 56

B

Front 57

A grid should be used whenever the anatomic part size exceeds:

A) 3 cm

B) 6 cm

C) 10 cm

D) 12 cm

Back 57

C

Front 58

The air gap technique uses a increased ________ instead of a grid.

A) kVp

B) mAs

C) SID

D) OID

Back 58

D