Lecture 4

Front 1

what is the function of a grid

Back 1

series of lead strips on edge which only allow the primary x-rays which are traveling in straight lines to reach the film

Front 2

does a grid help reduce scatter?

Back 2

yes

Front 3

grid focus

Back 3

the distance the grid needs to be from the x-ray tube (36-40 inches)

Front 4

grid cutoff

Back 4

occurs when x-ray tube is not in required 36-40 inch range. grid cutoff is a decrease in the # of x-rays that reach the film near the periphery due to the grid absorbing the x-rays

Front 5

what does the finished radiograph look like when grid cutoff occurs

Back 5

a lighter image than expected with white lines near the periphery

Front 6

4 reasons for grid cutoff

Back 6

1. incorrect grid focus

2. improper centering of the grid beneath the x-ray tube

3. tilting of the tube or the grid

4. focused grid upside down

Front 7

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

Back 7

grid efficiency

Front 8

what grid is more efficient; a 10:1 grid or a 5:1 grid?

Back 8

10:1. absorbs more scatter radiation.

Front 9

if the grid is stationary more lines that are finer are less apt to show up on a radiograph. fewer thick lines show up more.

Back 9

lines per centimeter

Front 10

a device that moves the grid back and forth under the table. it helps to prevent grid lines from showing

Back 10

potter-bucky diaphragm

Front 11

two different types of grids

Back 11

-focused

-unfocused or parallel

Front 12

purpose of film cassettes

Back 12

-rigid film holders

-protect the film from external light/damage

-keep x-ray film in close contact with the screens

- must be radiolucent

Front 13

what is the back of a cassette made of, and why is this what it is made of?

Back 13

lead, to decrease back scatter

Front 14

cassettes can easily be damaged. how are they commonly damaged in practice

Back 14

-stepped on (large animal)

-leak (urine)

Front 15

what are intensifying screens composed of?

Back 15

they are sheets of luminescent phosphor crystals on a cardboard or plastic base. two within each cassette- film gets sandwiched between them (crystals + x-rays = visible light)

Front 16

with the typical "screen film" used __% of our exposure on the film is due to visible light and __% is due to the x-rays directly

Back 16

95%, 5%

Front 17

type of film used which don't use screens of film cassettes. x-rays directly cause the latent image to be formed, not visible light

Back 17

non-screen films

Front 18

true or false: non-screen films need a lot more x-ray exposure and therefore more time to expose them

Back 18

true

Front 19

true or false: non screen films are less detailed

Back 19

false. non screen films give more detailed radiographs, but more exposure time to everyone involved

Front 20

what are non screen films commonly used for?

Back 20

dental film

Front 21

true or false: using screens leads to less radiation exposure, because you are using fewer x-rays to get your latent image.

Back 21

true

Front 22

what 3 things do screens (phosphor layer) need to have?

Back 22

1. high levels of x-ray absorption (determined by phosphor crystal type)

2. high level of x-ray to light conversion with the correct energy and color for the type of film used

3. must have little or no "afterglow"

Front 23

gives off blue light

Back 23

calcium tungstate

Front 24

gives off 4x the amount of light that calcium tungstate does. gives off green light

Back 24

rare earth elements