Grids

Question 1

Who built the first grid?

Answer 1

Gustave Bucky 1913. Built the first lead foil strips on the standing edge of the grid in order to trap scatter radiation.

Question 2

Who is Hollis E. Potter?

Answer 2

Created the first wire grid in 1915-1917. Shares the credit with Bucky on creating the grid

Question 3

When looking at the image, what does dark area represent?

Answer 3

Transmission of x-rays passing through the body and striking the IR.

Question 4

What does light areas on the image represent?

Answer 4

Absorption of x-ray or absence of x-ray striking the IR.

Question 5

As a general rule, use a grid when body parts exceed ___

Answer 5

10 cm

Question 6

As a general rule, use a grid when kVp is above ___

Answer 6

60

Question 7

Name the term that explains the height of the grid divided by interspace width.

Answer 7

Grid Ratio.

GR = (h/D)

Question 8

What is radiopaque material made from?

Answer 8

inexpensive lead and has high atomic #

Question 9

What does radiolucent material made from

Answer 9

interspaced materal, thicker than lead, either aluminum or plastic fiber, absorbs low energy scatter.

Question 10

If height were to stay the same and width were to decrease, ____

Answer 10

the ratio would increase. Inverse relationship.

Question 11

Grid ratios can range from ___ to ___.

Answer 11

4:1 to 16:1. The most common is the 8:1 to 10:1

Question 12

Which type of grid ratio will remove most of the scatter radiation?

Answer 12

Higher grids

Question 13

True or False: The higher the grid ratio, the higher the Bucky factor?

Answer 13

True

Question 14

What is a bucky factor?

Answer 14

to measure the penetration of primary and scatter radiation through the grid

Question 15

Which type of grid ratio will improve the contrast?

Answer 15

higher ratios

Question 16

What is a grid frequency?

Answer 16

the # of lead strips per inch or cm. Most common lays between 60 to 110 lines

Question 17

General rule: typically higher frequency grid has ___ lead strips.

Answer 17

thinner

Question 18

How much scatter does 5:1 cleans up?

Answer 18

85%

Question 19

How much scatter does 16:1 clean up?

Answer 19

97%

Question 20

In grid frequency, as contrast increases, ___

Answer 20

scatter decreases

Question 21

The simplest type of grid, easiest to manufacture, and absorbs scatter in one direction.

Answer 21

Parallel grid

Question 22

The undesirable absorption of primary x-ray by the grid.

Answer 22

gird cutoff

Question 23

More efficient than parallel grid in cleaning up scatter radiation, manufacturing is not excessively expensive.

Answer 23

crossed grids

Question 24

Name the three disadvantages of crossed grids

Answer 24

1) positioning is critical
2) Tilt-table techniques are possible if tube and table are aligned
3) Exposure technique requires higher PT radiation dose.

Question 25

Difficult to manufacture but has the same properties of parallel grids expect when positioned properly exhibit no grid cutoff.

Answer 25

Focused Grid

Question 26

Three characteristics of focused linear grids

Answer 26

1) Proper centering 2) Preset SID 3) Careful alignment

Question 27

What is a reciprocating grid?

Answer 27

a moving grid that is motor-driven. The total distance of the drive is 2 cm.

Question 28

What is an oscillating grid?

Answer 28

A powerful electromagnet pulling the grid to one of the four sides. The gird moves (oscillates) in a circular motion for 20 to 30 seconds.

Question 29

Disadvantages of moving grids

Answer 29

Distance between patient and image receptor is increased. | Magnification and image blur due to increasing distance.

Question 30

True or False: Moving grids are the technique of choice and widely used

Answer 30

True

Question 31

As a general rule, below 90 kVp use a grid of ___. About 90 kVp use a grid of ___.

Answer 31

below - 8:1 | above - 10:1

Question 32

As grid ratio increases, ______

Answer 32

radiographic density decreases. (inverse relationship)

Question 33

What is a grid selectivity?

Answer 33

describe grid's ability to allow primary radiation to reach image receptor and prevent scatter. k = (contrast with grid/contrast without grid) Ranges of 1.5 or 3.5 (times better with grids)

Question 34

Commonly seen in mobile or beside radiography grid error.

Answer 34

Off-center and off-focus

Question 35

Grid problems results in ____

Answer 35

underexposed image or underexposed edges of images

Question 36

What is an off-level grid error?

Answer 36

Grid or tube was tilted. Cutoff happens around the image.

Question 37

what is an off-center grid error?

Answer 37

A lateral detent problem, One side of the image was cut-off.

Question 38

What will a off focus grid error look like?

Answer 38

Image appears blurry with some grid cutoff around the sides

Question 39

What is an air technique?

Answer 39

IR is moved 10 to 15 cm away from the patient. A portion of the scatter radiation will never hit the IR.

Question 40

What are the disadvantages with air technique?

Answer 40

increase mA 10% for every centimeter of air gap. Technique is about the same for 8:1 grid. Higher dose of PT, increase SID and OID, image blur a bit.