Technique Ch. 18

Front 1

Grid

Back 1

Is a device used to improve the contrast of the radiographic image by absorbing scatter radiation before it can reach the image receptor (IR)

Front 2

The patient

Back 2

What is the primary source of scatter radiation during an x-ray

Front 3

NO

Back 3

Does scatter radiation have diagnostic value?

Front 4

Pass-through unaffected (transmission)

Be absorbed

(absorption)

Interact and change direction (scatter)

Back 4

When x-rays interact with patients, what three things can they do?

Front 5

Dark areas

Back 5

Transmission radiation is responsible for

Front 6

Light areas

Back 6

Absorption radiation is responsible for

Front 7

Lowers contrast

Back 7

Scatter radiation lowers what?

Front 8

scatter radiation

Back 8

Primary radiation that interacts and, as a result of this interaction, changes direction is known as

Front 9

A grid

Back 9

Increase technique when using what?

Front 10

Increased kVP

Patient thickness

Larger field sizes

Decreases in atomic number of the tissue

Back 10

The amount of scatter radiation increases with

Front 11

Patients with part thickness greater than 10cm

kVp greater than 60

Back 11

Grades are recommended when..

when..

Front 12

Radio plaque lead strips separated by radiolucent interspace material

Back 12

Grids are made of

Front 13

Plastic or aluminum cover

Back 13

The lead strips of a grid are protected by

Front 14

Foil, aluminum

Back 14

The lead strips are a very thin ____ and the interspace material is thicker and usually made of _____

Front 15

1913, Gustav Bucky

Back 15

The very first grid was made in ____, by _____

Front 16

Gustav Bucky's first grid

Back 16

Crude design by today's standard.

Wide LED strips, two inches apart.

Crosshatch design.

Greatly improved image contrast.

Could see checkerboard gridlines in image

Front 17

Dr. Hollis Potter, 1920

Back 17

Made improvements to the Bucky design by realigning thinner lead strips strips to run in One Direction.

Invented the Potter Bucky diaphram ( moving grid)

Improvements paved way for modern grid design and functionality

Front 18

Potter Bucky diaphragm

Back 18

Device that allowed the grid to move during the exposure to blur out gridlines, making them invisible

Front 19

Benefits of grids

Back 19

Allows primary radiation to reach image receptor.

Absorbs most scatter radiation

Front 20

Primary disadvantages of using grids

Back 20

Gridlines on film

Some absorption of primary radiation if not used properly

Front 21

Low-dose grids

Back 21

Interspace material and grid encasement are made of carbon fiber

Front 22

Carbon fiber interspace grids

Back 22

Are preferred when using low kvp techniques where their application can contribute to lower patient dose, such as in mammography

Front 23

Grid ratio

Back 23

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

= H/D

Front 24

H/D

3 / 0.25 = 12

12:1 grid ratio

Back 24

If the lead strips are 3 mm high and are separated by an interspace of 0.25 mm, what is the grid ratio?

Front 25

Decrease

Back 25

If the height of the grid is a constant, decreasing the distance between the lead strips would result in a ____ in the grid ratio

Think about it

Front 26

Higher grid ratio

Back 26

Is more effective in removing scatter

Requires more exposure

Front 27

5:1 to 17:1

Back 27

Typical grid ratio range:

Front 28

Digital grids and analog (film/screen) grids

Back 28

Grid ratio can vary between what two types of grids

Front 29

4

Back 29

What is the conversion factor at a grid ratio of 8:1

Front 30

Absorption, contrast

Increase

Back 30

The higher the grid ratio, the higher the ____, which leads to higher ____

Increase or decrease exposure?

Front 31

Increase

Back 31

If the height of the grid is a constant, decreasing the distance between the lead strips would result in a ____ in the grid ratio

Think about it

Hint 31

Front 32

Grid frequency

Back 32

The number of grid lines per inch or centimeter

Front 33

The grid lead content

Back 33

What is most important in determining the Grid's efficiency at cleaning up scatter

Measured in mass per unit area: g/cm^2

Front 34

The total quantity of lead in the grid

Back 34

By combining information about grid ratio and frequency, you can determine

Front 35

Higher, lower

Back 35

The lead content is greater in a grid that has a ____ grid ratio and ____ grid frequency

Front 36

Increases

Back 36

As the lead content of a grid increases, the ability of the grid to remove scatter and improve contrast..

Front 37

Grid cutoff

Back 37

Is the undesirable interception of primary beam photons, by the grid strips

The results of the primary beam being angled into the lead strips

Front 38

Cross-hatched or crisscross grids

Back 38

2 linear grids placed on top of one another so that the lead strips form a crisscross pattern

Not widely used due to positioning limitations and dose

Front 39

Linear grids

Back 39

A grid with lead strips running in only one direction

Front 40

Linear grid

Back 40

Allows primary beam to be angled along direction that lines are running.

Allows for angling tube toward head or feet of patient since the strips run along long access of the table

Front 41

Short access grids

Back 41

Has grid lines that run across the short access of the grid.

Are useful for mobile chest procedures to decrease the chance of grid cut off when the image receptor is placed clockwise

Front 42

Focused linear grids

Back 42

Lead strips angled to match Divergence of beam

Primary beam will align with interspace material

Must be used with a range of SIDs

If these led strips were extended, the strips would intersect along the line in space known as the Convergence Line

Beam is diverging from tube (flashlight)

Primary beam has to align with interspace

Hint 42

Front 43

Higher

Back 43

_____ ratio grids require careful alignment with tube

Front 44

Primary beam

Back 44

Beam before it hits patient

Front 45

Secondary beam (remnant)

Back 45

Beam after patient but before IR

Front 46

Parallel linear grids

Back 46

All lead strips parallel to one another.

Absorbs large amount of primary beam resulting in some cut off.

Least expensive, but unpopular due to positioning limitations

Function best at long as opposed to short, SID

Front 47

Stationary grids

Back 47

Words that can be attached to image receptor cassette.

Grid lines on the image will usually be noticed on close inspection

Front 48

Stationary, Potter-Bucky diaphragm

Back 48

A grid is used either in a ____ position or mounted in a ____

Front 49

Potter-Bucky diaphragm (Bucky)

Back 49

The most common use of the grid is for procedures using the

Involves reciprocating or oscillating devices

Front 50

Reciprocating grid

Back 50

A motor drives the grid back and forth during the exposure for a total distance of no more than 2 to 3 cm

Front 51

Oscillating grid

Back 51

And electromagnet pulls the grid to one side and then releases it during exposure. The Grid oscillates in a circular motion with the grade frame

Front 52

Whenever a grid is used to remove scatter

Back 52

Image receptor exposure of radiographic go down

Exposure factors must be increased to compensate for a lack of image receptor exposure

Front 53

Grid conversion factor or Bucky Factor

Back 53

Required increase in technique due to using grid can be calculated by using

Front 54

Back 54

A satisfactory chest radiograph is produced using 5 mAs at 85 kvp without a grid. A second image is requested using a 12:1 grid. What mAs is needed to produce a second satisfactory image?

Hint 54

Front 55

Back 55

When converting from one grid ratio to another, the following formula is used

Front 56

Back 56

A satisfactory abdominal image is produced using a 8:1 grid, 35 mAs, and 85 kvp. A second image is requested using a 12:1 grid. Calculate what mAs is needed to produce a second satisfactory image

Hint 56

Front 57

Proper alignment between x-ray tube and grid.

Improper alignment results in Cut Off

Back 57

Very important avoidable grid error

Front 58

Off level Grid error

Back 58

A grid error that occurs when the tube is angled across the long axis of the grid strips. This can be the result of improper tube or grid positioning

Can occur with a focused grid and is the only positioning are possible with a parallel grid

Hint 58

Front 59

Off-level error

Back 59

When this error occurs, there is an undesirable absorption of primary radiation, which results in a radiograph with a decrease in exposure across the entire image

Front 60

Off-center grid error

Back 60

The X-ray tube must be centered along the central axis of a focused grid to prevent this.

The center grid strips are perpendicular and become more and more inclined away from the center.

This design coincides with the Divergence of the X-ray beam from the tube

Hint 60

Front 61

Off center grid (off-axis or lateral decentering)

Back 61

This error results in a decrease in exposure across the entire image

Front 62

Off focus grid error

Back 62

When a grid is used at a distance other than that specified as the focal range, this error resultsCauses grid cutoff along peripheral edges of the image

Causes grid cutoff along peripheral edges of the image

Causes grid cutoff along peripheral edges of the image

Hint 62

Front 63

Off-focused grid error

Back 63

Results in Grid cutoff along the peripheral edges of the image

Front 64

Upside down grid error

Back 64

Causes severe peripheral grid cutoff.

Radiation will pass through the grid along the Central Access where the grid strips are most perpendicular and radiation will be increasingly absorbed away from the center

Hint 64

Front 65

Upside down grid error

Back 65

Front 66

Moire effect

Back 66

Is a grid error that occurs with digital IR systems when the grid lines are captured and scanned parallel to the scan lines in the Imaging plate readers

Can be prevented by using high-frequency grids design for computed radiography

Hint 66

Front 67

Grid errors

Back 67

Off level.

Central Ray angulation across grid

lines.

Off center.

Off focus.

Upside down.

Moire effect (grid aliasing)

Front 68

Air-Gap technique

Back 68

Alternative to grid use.

Scatter radiation is lost in air space between patient and receptor.

10 inch air gap has similar clean up of 15:1 grid.

SID needs to increase equal amount to maintain image Revolution

Hint 68

Front 69

Air gap technique

Back 69

The _____ technique reduces the amount of scatter radiation reaching the image receptor

Front 70

Digital receptors, increase, 50

Back 70

When _____ are used, increasing kvp values is strongly recommended. Use 15% rule and an _____ in kVp can be offset with a ___% reduction in mAs

Front 71

Selectivity

Back 71

Grids that absorb a greater amount of scatter then primary radiation are described as having a greater degree of

Front 72

Contrast Improvement Factor

Back 72

A scatter increases, contrast decreases, as will the...