Chapter 18 Notes

Question 1

a grid is used to

Answer 1

improve image contrast

Question 2

grids are made of

Answer 2

lead strips alternating with an interspace material (usually aluminum)

Question 3

what grids are more efficient at removing scatter

Answer 3

grids with higher ratios and lead content

Question 4

what technical factor should be increased when using a grid

Answer 4

mAs

Question 5

alternative to use of a grid

Answer 5

air-gap technique or grid replacement software applications

Question 6

what is the primary source of scatter radiation

Answer 6

the patient

Question 7

scatter radiation has no _____

Answer 7

diagnostic value

Question 8

transmission on a radiograph

Answer 8

dark areas of image

Question 9

absorption on a radiograph

Answer 9

light areas of image

Question 10

what does scatter do to contrast

Answer 10

lowers contrast

Question 11

scatter increases as

Answer 11

kVp increases; field size increases; thickness of part increases; and atomic number decreases

Question 12

grids are recommended in patients with

Answer 12

part thickness greater than 10 cm

Question 13

grids are recommended with kVp setting

Answer 13

greater than 60

Question 14

who created grids

Answer 14

Dr. Gustav Bucky

Question 15

when were grids created

Answer 15

1913

Question 16

what was the design of early grids

Answer 16

wide lead strips (2” apart) with a crosshatched design

Question 17

who made improvements to the early grid

Answer 17

Dr. Hollis Potter

Question 18

how did Dr. Hollis Potter improve the grid

Answer 18

realigned lead strips to run in one direction; thinner strips

Question 19

grid ratio =

Answer 19

height of lead strips / thickness of interspace material
(h/D)

Question 20

typical grid ratio range

Answer 20

5:1 to 17:1

Question 21

grid frequency

Answer 21

number of lead strips per inch or cm

Question 22

grid frequency range

Answer 22

60-200 lines/in (lpi)

Question 23

most common grid frequency

Answer 23

85-103 lpi

Question 24

lead content measured in

Answer 24

mass per unit area
gcm(squared)

Question 25

as lead content increases, removal of scatter _____; therefore contrast _____

Answer 25

increases; increases

Question 26

linear grid pattern

Answer 26

grid lines running in one direction only

Question 27

cross-hatched grids

Answer 27

two parallel grids; one on top of the other

Question 28

the cross-hatched grid is not widely used due to

Answer 28

positioning limitations and dose

Question 29

a linear grid allows

Answer 29

primary beam to be angled along direction that lines are running (typically along long axis of table)

Question 30

short axis grids

Answer 30

grid lines run across short axis of grid

Question 31

a short axis grid is useful for

Answer 31

portable chest procedures when IR is placed crosswise

Question 32

focused linear grids

Answer 32

lead strips angled to match divergence of beam

Question 33

focused linear grids must be used within

Answer 33

range of SIDs

Question 34

what grid is least expensive but unpopular due to positioning limitations

Answer 34

parallel linear grids

Question 35

stationary grids

Answer 35

grids that can be attached to IR cassette

Question 36

Potter-Bucky diaphragm

Answer 36

moves grid during exposure

Question 37

reciprocating grid movement

Answer 37

small motor drives grid back and forth during exposure

Question 38

oscillating grid movement

Answer 38

electromagnet pulls grid to one side, releasing it during exposure

Question 39

GCF stands for

Answer 39

grid conversion factor

Question 40

GCF =

Answer 40

mAs with grid / mAs without grid

Question 41

GCF is _____ dependent

Answer 41

kVp

Question 42

grid conversion

Answer 42

mAs1/mAs2 = GCF1/GCF2

Question 43

contrast improvement ability

Answer 43

"K" factor

Question 44

K factor typically ranges between

Answer 44

1.5 and 3.5

Question 45

higher "K" factor grids offer

Answer 45

higher contrast

Question 46

Moire effect

Answer 46

grid lines parallel to scan lines

Question 47

how can Moire effect be prevented

Answer 47

by using high-frequency grids designed for computed radiography

Question 48

what air gap has similar clean-up of 15:1 grid

Answer 48

10"

Question 49

grid replacement software is designed to

Answer 49

produce a grid-like image with no grid use

Question 50

grid suppression software

Answer 50

removes grid lines from final image for review