Ch. 12 Scatter Control

Question 1

scatter in diagnostic x-ray is primarily due to this type of interaction

Answer 1

Compton effect

Question 2

what are the 2 major factors that affect scatter production

Answer 2

• tissue volume
• kVp

Question 3

what is tissue volume dependent on

Answer 3

part thickness and field size

Question 4

scatter adds unwanted radiation to the image, what do we call this

Answer 4

fog

Question 5

beam restrictions do these two things

Answer 5

• limits patient dose
• reduces scatter production

Question 6

relationship between collimation and field size

Answer 6

inverse

Question 7

increasing collimation does what to field size

Answer 7

decrease field size

Question 8

increasing collimation does what to scatter production

Answer 8

decreases scatter production

Question 9

significant changes in collimation will require this

Answer 9

adjusted mAs

Question 9

going from a 14x17 field size to a 4x4 field size may require what

Answer 9

more mAs

Question 10

essentially a flat piece of lead with a small hole in it, attaches to the collimator

Answer 10

aperture diaphragms

Question 11

long tube/cone that attaches to the collimator, most often used for dental imaging today, can also be used for small parts such as nasal bones and fingers. These devices help to limit both scatter and beam divergence

Answer 11

cones/cylinders

Question 12

most used form beam restriction, this is the part of the x-ray tube that we use to set field size. Typically consists of 2-3 lead shutters that can be adjusted using controls on the collimator

Answer 12

collimators

Question 13

also called positive beam-limiting devices (PBL). these are essentially the same as standard collimators, the difference is that these automatically set selected field size depending on what exam is being completed. a lot of collimators today are a form of PBL

Answer 13

automatic collimators

Question 14

who invented the radiographic grid and when

Answer 14

Gustave Bucky - 1913

Question 15

number of lead strips per unit length

Answer 15

grid frequency

Question 16

the ratio of the height of the lead strips and the distance between them

Answer 16

grid ratio

Question 17

what are the 2 types of grid focus

Answer 17

• parallel grid
• focused grid

Question 18

what are the 4 types of grid

Answer 18

• wafer grid
• grid cassette
• grid cap
• reciprocating grid

Question 19

stationary, same size as IR, usually taped to secure it to IR

Answer 19

wafer grid

Question 20

stationary, IR with a permanent grid mounted to the front surface

Answer 20

grid cassette

Question 21

stationary, very similar to the wafer, but is designed to hold the IR, so no tape is required to secure it. Most common grid type

Answer 21

grid cap

Question 22

dynamic, they slightly move while the image is being taken, so as to blur out grid lines. these are built into wall stands and table buckys

Answer 22

reciprocating grid

Question 23

the decrease in the number of transmitted photons that reach the IR due to grid misalignment

Answer 23

grid cutoff

Question 24

because focused grids are designed to match beam divergence, if they are place upside down, then they will cutoff most of the radiation before it can reach the IR

Answer 24

upside down focused

Question 25

most common type of cutoff, happens when the IR with grid is tilted and the CR is not adjusted to match. also the only type that can occur with both focused and parallel grids

Answer 25

off-level

Question 26

happens with focused grids when the CR is not aligned to the center of the IR, once again, because focused grids are designed to work with beam divergence

Answer 26

off-center

Question 27

occurs when SID is outside of the focal range of the focused grid, meaning the tube is either too close or too far away from the IR at the time of exposure. This results in images with not enough exposure along the edges of the image

Answer 27

off focused

Question 28

zebra stripe pattern that occurs when the grid frequency of a stationary grid used in CR imaging is similar to the laser scanning frequency of the CR reader

Answer 28

moire effect

Question 29

what can help eliminate moire effect

Answer 29

- using higher frequency grids - using moving grids with CR

Question 30

method for limiting the scatter reaching the image receptor. scatter will miss the image receptor if there is increased distance between the patient and the image receptor (increased OID)

Answer 30

air gap technique

Question 31

the simplest type of beam-restricting device, constructed of a flat piece of lead that has a hole in it

Answer 31

aperture diaphragm

Question 32

automatically limits the size and shape of the primary beam to the size and shape of the image receptor

Answer 32

automatic collimator

Question 33

changes the shape and size of the primary beam; located just below the x-ray tube housing

Answer 33

beam-restricting device

Question 34

refers to a decrease in the size of the projected radiation field also known as collimation

Answer 34

beam restriction

Question 35

the potter-bucky diaphragm located directly below the radiographic tabletop, which contains the grid and holds the image receptor

Answer 35

bucky

Question 36

can be used to determine the adjustment in milliampere/second needed when changing from using a grid to non-grid (or vice versa) or for changing to grids with different grid ratios

Answer 36

bucky factor

Question 37

refers to a decrease in the size of the projected radiation field, also known as beam restriction

Answer 37

collimation

Question 38

located immediately below the tube window where the entrance shutters limit the x-ray beam field size

Answer 38

collimator

Question 39

essentially an aperture diaphragm that has an extended flange attached

Answer 39

cone

Question 40

an imaginary line if points were connected along the length of a linear focused grid

Answer 40

convergent line

Question 41

an imaginary point, if imaginary lines were drawn from each of the lead lines in a linear focused grid

Answer 41

convergent point

Question 42

has lead line that run at a right angle to one another

Answer 42

cross-hatched grid; crossed grid

Question 43

essentially an aperture diaphragm that has an extended flange attached to it

Answer 43

cylinder

Question 44

the distance between the grid and the convergent line or point; also known as the grid radius

Answer 44

focal distance

Question 45

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

Answer 45

focal range

Question 46

has lead line that are angled, or canted, to approximately match the angle of divergence of the primary beam

Answer 46

focused grid

Question 47

a device that has very thin lead strips with radiolucent interspaces; intended to absorb scatter radiation emitted from the patient before it strikes the IR

Answer 47

grid

Question 48

contains a permanently mounted grid and allows the IR to slide in behind it

Answer 48

grid cap

Question 49

an IR that has a grid permanently mounted to its front surface

Answer 49

grid cassette

Question 50

can be used to determine the adjustment in milliampere/second needed when changing from using a grid to non-grid (or vice versa) or for changing to grids with different grid ratios; also called the bucky factor

Answer 50

grid conversion factor (GCF)

Question 51

a decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid

Answer 51

grid cutoff

Question 52

the orientation of a grid's lead lines to one another

Answer 52

grid focus

Question 53

expresses the number of lead lines per unit length in inches, centimeters, or both

Answer 53

grid frequency

Question 54

refers to the linear pattern of the lead lines of a grid

Answer 54

grid pattern

Question 55

the ratio of the height of the lead strips to the distance between them

Answer 55

grid ratio

Question 56

radiolucent strips between the lead lines of a grid, generally made of aluminum

Answer 56

interspace material

Question 57

changes the shape and size of the projected x-ray field; similar to an aperture diaphragm

Answer 57

lead mask

Question 58

has lead lines that run in one direction only

Answer 58

linear grid

Question 59

a zebra pattern artifact that can occur during computed radiography imaging if the grid frequency is similar to the laser scanning frequency or if a grid cassette is placed in a bucky

Answer 59

Moire effect

Question 60

has lead lines that run parallel to one another; also called a parallel grid

Answer 60

non-focused grid

Question 61

has lead lines that run parallel to one another; also called a non-focused grid

Answer 61

parallel grid

Question 62

automatically limits the size and shape of the primary beam to the size and shape of the image receptor; also called automatic collimator

Answer 62

positive beam-limiting (PBL) device

Question 63

a stationary grid placed on top of the image receptor

Answer 63

wafer grid