Unit 3: Grids

Question 1

Function of a grid

Answer 1

to absorb a large amount of scattered radiation before it reaches the IR

Question 2

Transmission is responsible for:

Answer 2

dark areas

Question 3

Absorption responsible for

Answer 3

light areas

Question 4

The absorption of x-rays in the patient, occurs from?

Answer 4

Photoelectric Interaction

Question 5

Scattered x-rays

Answer 5

Creat noise
Lower image contrast and overall quality

Question 6

Image forming x-rays

Answer 6

1. photons that reach IR
2. transmission
3. compton scatter

Question 7

Scatter definition

Answer 7

X rays in the primary beam that interact within the patient which cause them to change direction and lose energy.

Question 7

Each time an xray photon scatteres, what happens to its energy?

Answer 7

Decreases

Question 8

Are scattered x-rays in the primary beam?

Answer 8

No

Question 9

X-rays only scatter when:

Answer 9

they interact w/ the pt or other matter

Question 10

Primary beam is made up of:

Answer 10

Brems
Characteristic
Stem (off focus)
(no scattered xrays)

Question 11

Off focus radiation

Answer 11

Radiation that escapes the collimators (this will image things not w/in the collimated field)

Question 12

When do x-rays scatter

Answer 12

When interacting w/ tissues in the pt., compton interactions, and some from classical interactions

Question 12

Scattered x rays reaching the IR are produced almost entirely from

Answer 12

Compton Interactions

Question 13

Things that increase the intensity (quantity) of scattered radiation

Answer 13

1. Higher kVp techniques create more scatter. (bigger beam = higher energy = more forward scatter)
2. Thicker body parts create more scatter.
3. Increasing field size (decreasing collimation) creates more scatter.
4. Higher tissue density body parts create more scatter.
5. Water rich tissues produce a greater amount of scatter.

Question 14

What is tissue (mass) density?

Answer 14

the number of atoms in a specific volume of tissue.

Question 14

“ how tightly packed” atoms are in certain tissues.

Answer 14

tissue (mass) density

Question 15

Compton Scatter is just as likely to occur in an atom soft tissue and bone.
The increased presence of water in soft tissue makes it just as likely that scatter will occur in bone and soft tissue, despite the density of bone vs. soft tissue.

Question 16

a muscular, or obese, or hypersthenic body build creates ____ scattered radiation compared to a hyposthenic, asthenic, or emaciated body build, with all other factors remaining constant.

Answer 16

More

Question 17

What do compton interactions “decide”

Answer 17

direction and angle of degree that x-rays scatter

Question 18

Purpose of grid

Answer 18

Catch scatter before it can reach the IR
Improves image contrast.

Question 19

Recall

Answer 19

the function of contrast is to make “spatial resolution visible”.

Question 20

contrast allows:

Answer 20

visibility of anatomy to increase accuracy of image interpretation

Question 21

Does scatter decrease SR?

Answer 21

No - just the visibility of SR

Question 22

SR is only determined by ______ factors?

Answer 22

Geometric

Question 23

Grid caps

Answer 23

Grid frames used during CR

Question 23

Grids were first developed by _________ and Gustav Bucky in the early 1900’s.

Answer 23

Hollis Potter Gustav Bucky

Question 24

table grid device used to be called

Answer 24

potter-bucky diaphragm

Question 25

Who made improvments to the grid?

Answer 25

Dr. Hollis Potter

Question 25

Hollis did what to improve grids?

Answer 25

Realigned the lead strips to run in one direction Moved grid during exposure to make lines invisible

Question 26

Grids absorb scattered radiation which means your radiograph will:

Answer 26

Have higher visible image contrast. Have better visibility of anatomy. Have less noise.

Question 27

Methods to Reduce Scattered Radiation Reaching the IR

Answer 27

Use the lowest acceptable kVp for each body part. Always collimate to the smallest possible field. Compress the part if possible Use a grid. Air gap technique

Question 28

to use a grid with body parts measuring over

Answer 28

10-12 cm

Question 29

to use a grid when using a kVp of

Answer 29

>60

Question 30

Calipers

Answer 30

measure thickness in cm. during film era

Question 31

Compression bands

Answer 31

reduce scatter

Question 31

Types of Grids

Answer 31

Linear focused/Non-parallel Linear non-focused or parallel Crosshatch Long dimension Short dimension

Question 31

Long dimension grids

Answer 31

grid lines run parallel to the long axis.

Question 32

Short dimension grids

Answer 32

grid lines run perpendicular to the long axis

Question 32

Most common grid type

Answer 32

Linear focused

Question 32

Grid patterns

Answer 32

Criss-cross or cross-hatch Linear (parallel and focused)

Question 33

When are criss-cross/cross-hatch used?

Answer 33

In fluro and IR where there is a lot of scatter

Question 34

Linear pattern is used for:

Answer 34

Wall, table, portable

Question 34

Grid Cutoff

Answer 34

When the grid eats up lots of good info

Question 35

Why can't you angle the beam with cross hatch?

Answer 35

Cutoff

Question 35

Can you angle the beam with linear?

Answer 35

Yes, only cephalad or caudad because of the direction of lead strips