RAD 214: Unit 4 Scatter Control

What is the frequency range for low frequency grids?

40 - 50 lines/cm (100-120 lines/inch)

What is the frequency range for medium frequency grids?

50-60 lines/cm (120 - 150 lines/inch)

What is the frequency range for high frequency grids?

60 - 70+ lines/cm (150-170+ lines/inch)

If 24 mAs and a 6:1 grid results in an excellent radiograph, how much mAs is needed with a 5:1 grid? A. 16 mAs. B. 20 mAs. C. 28.8 mAs. D. 36 mAs.

A. 16 mAs.

_____________________ collimation means _________________ field size. A. Decreasing; increasing B. Increasing; increasing C. Decreasing; decreasing D. none of the above

A. Decreasing; increasing

Adding a grid or increasing grid ratio results in an increase in patient dose. A. True B. False

A. True

Focused grids are more effective than parallel grids in absorbing scatter radiation and allowing transmitted radiation to reach the IR. A. True B. False

A. True

Scatter radiation is of no value in radiographic imaging. A. True B. False

A. True

To overcome the decrease in sharpness caused by the air gap technique, an increase in SID is required. A. True B. False

A. True

The beam-restriction device that results in images with the most unsharpness around the edge of the image is the A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

A. aperture diaphragm

The simplest type of beam-restricting device is a flat piece of lead with a hole in it called a(n) A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

A. aperture diaphragm

The higher the grid ratio, the _____________ the scatter clean up and the _____________________ the radiographic contrast. A. better; higher B. worse; lower C. better; lower D. worse; higher

A. better; higher

If all the convergent points were connected along the length of the grid they would form the A. convergent line B. focal distance C. convergent point D. focal range

A. convergent line

A significant amount of collimation will have what effect on the amount of radiation reaching the IR A. reduced B. increased C. the same D. none of the above

A. reduced

The unrestricted primary x-ray beam is A. round B. oval C. square D. rectangular

A. round

The probability of a Compton interaction occurring is related to A. the energy of the x-ray photon B. the atomic number of the matter C. the mAs used D. all of the above

A. the energy of the x-ray photon

The cutoff that appears as a strip of appropriate density in the middle of the image and a significant loss of density on both sides is A. upside-down focused B. off-level C. off-center D. off-focus

A. upside-down focused

The type of grid that is usually taped to the front of an IR is the A. wafer grid B. bucky C. grid cap D. grid cassette

A. wafer grid

What are some types of beam-restricting devices?

Aperture Diaphragm Cones and Cylinders Collimators

NEED TO KNOW!! How do you compensate for collimation?

As collimation increases, radiation reaching IR decreases, mAs needs to be increased to compensate & vise versa

What does an automatic collimator do?

Automatically collimates to size of IR allows reducing field size smaller than IR Automatically adjusts for changes in SID

If a shoulder examination is done using an 8:1 ratio grid and 12 mAs, how much mAs should be used if the examination must be done tabletop (no grid)? A. 1.5 mAs. B. 3 mAs. C. 48 mAs. D. 96 mAs

B. 3 mAs.

What is the grid ratio if the grid frequency is 100 lines/inch, and the lead strips are 1.8 mm high and 0.3 mm apart? A. 5:1. B. 6:1. C. 8:1. D. 12:1.

B. 6:1.

Beam-restricting devices are located just above the tube housing. A. True B. False

B. False

Grids absorb almost all of the scatter radiation and allow all of the transmitted photons to pass through to the IR. A. True B. False

B. False

It is safe to assume that the x-ray beam field size and the light field size are exactly the same. A. True B. False

B. False

The grid limits the amount of scatter radiation produced in the patient. A. True B. False

B. False

The grid used for the air gap technique should be high frequency. A. True B. False

B. False

When using automatic collimation, collimating to the anatomy of interest is an unnecessary waste of time; the beam is already collimated. A. True B. False

B. False

To compensate for some of the loss of recorded detail due to the large OID used with the air gap technique, the ________ should be increased as well. A. grid ratio B. SID C. focal spot size D. A and B

B. SID

The grid is located A. just below the x-ray tube window B. between the patient and IR C. just below the IR D. between the x-ray tube and the patient

B. between the patient and IR

The grid is part of a device located just below the tabletop that also includes a tray to hold the IR. This device is the A. wafer grid B. bucky C. grid cap D. grid cassette

B. bucky

The beam-restriction device that includes a visible light projecting the x-ray field size onto the patient is the A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

B. collimator

The most easily adjusted radiographic beam-restricting device is the A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

B. collimator

The most effective and often used radiographic beam-restriction device is the A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

B. collimator

The distance between the grid and the convergent line is the A. convergent line B. focal distance C. convergent point D. focal range

B. focal distance

A short-dimension grid A. is typically used for most examinations B. has lead strips running perpendicular to the long axis of the grid C. has lead strips running parallel to the long axis of the grid D. A and B

B. has lead strips running perpendicular to the long axis of the grid

As compared with lower kVp exposures, when using high kVp will result in a scattered photon that is of ________ energy. A. lower B. higher C. the same D. half

B. higher

The purpose of automatic collimation is A. improved image quality B. limiting patient exposure C. increasing the cost of equipment D, none of the above

B. limiting patient exposure

The only grid cutoff error that can occur with a parallel grid is A. upside-down focused B. off-level C. off-center D. off-focus

B. off-level

When the x-ray beam is angled across the lead strips you have _________ cutoff. A. upside-down focused B. off-level C. off-center D. off-focus

B. off-level

Anyone in the room during an exposure must wear a lead apron to absorb the scatter radiation produced in the A. table B. patient C. air D. beam

B. patient

The material between the lead strips of a grid must be A. radiopaque B. radiolucent C. made of lead D. made of tungsten

B. radiolucent

The relationship between the height of the lead strips and the distance between them is the grid A. number B. ratio C. frequency D. rating

B. ratio

For a lateral lumbar spine, placing a lead shield on the table behind the area of exposure A. reduces the scatter exiting the patient B. reduces the scatter reaching the IR C. increases the scatter reaching the IR D. A and B

B. reduces the scatter reaching the IR

A focused grid's lead strips are angled to match A. the anode angle B. the angle of the x-rays in the primary beam C. the angle of the scattered photons leaving the patient D. the tube angulation

B. the angle of the x-rays in the primary beam

Grids are typically only used when the part measures more than ________ cm and ______ kVp is needed for the examination. A. 5; 50 B. 10; 50 C. 10; 60 D. 15; 65

C. 10; 60

If a tabletop exposure (no grid) of a humerus requires 2.5 mAs, how much mAs is needed if a 12:1 ratio grid is added? A. 0.21 mAs. B. 0.5 mAs. C. 12.5 mAs. D. 30 mAs.

C. 12.5 mAs.

What is the grid ratio if the lead strips are 2.4 mm high, 0.02 mm wide, and 0.3 mm apart? A. 5:1. B. 61. C. 8:1. D. 12:1.

C. 8:1.

For radiographic procedures, scatter radiation is primarily the result of A. Photoelectric interaction B. Pair production C. Compton interaction D. Classical scattering

C. Compton interaction

The formula for the grid conversion factor is A. GCF = mAs without grid/mAs with grid B. GCF = mAs with grid - mAs without grid C. GCF = mAs with grid/mAs without grid D. GCF = mAs without grid - mAs with grid

C. GCF = mAs with grid/mAs without grid

Which of the following is the formula used to determine grid ratio? A. Grid ratio = distance between the lead strips/height of the lead strips. B. Grid ratio = width of the lead strips/height of the lead strips. C. Grid ratio = height of the lead strips/distance between the lead strips. D. Grid ratio = height of the lead strips/width of the lead strips.

C. Grid ratio = height of the lead strips/distance between the lead strips.

The air gap technique is based on creating a gap by increasing the ______ A. SID B. SOD C. OID D. mAs

C. OID

When imaging the pelvis, changing from 14 × 17 collimation to 8 × 10 collimation requires A. an increase in kVp B. a decrease in kVp C. an increase in mAs D. a decrease in mAs

C. an increase in mAs

The reason the grid in the bucky reciprocates is to A. absorb more scatter radiation B. allow more transmitted radiation to reach the IR C. blur out the grid lines D. all of the above

C. blur out the grid lines

A flat piece of lead with a hole in it that has a flange directed toward the patient is a(n) A. aperture diaphragm B. collimator C. cone or cylinder D. none of the above

C. cone or cylinder

The location in space where all the lines extended from the lead strips meet is the A. convergent line B. focal distance C. convergent point D. focal range

C. convergent point

Increasing collimation (decreasing the field size) results in A. increased scatter production and higher contrast B. increased scatter production and lower contrast C. decreased scatter production and higher contrast D. decreased scatter production and lower contrast

C. decreased scatter production and higher contrast

The number of lead lines per inch or centimeter is the grid A. number B. ratio C. frequency D. rating

C. frequency

The type of grid that is permanently mounted but includes a channel for the IR to slide into is the A. wafer grid B. bucky C. grid cap D. grid cassette

C. grid cap

Absorption of transmitted photons by a grid caused by misalignment is A. grid focus B. grid reduction C. grid cutoff D. transmission reduction

C. grid cutoff

To compensate for the reduction of radiation reaching the IR when a grid is used, ___________ is typically increased. A. SID B. kVp C. mAs D. OID

C. mAs

The formula to use when changing from one grid to another is A. mAs1/mAs2 = GCF2/GCF1 B. mAs1/mAs2 = (GCF2)2/GCF1)2 C. mAs1/mAs2 = GCF1/GCF2 D. mAs1/mAs2 = (GCF1)2/GCF2)2

C. mAs1/mAs2 = GCF1/GCF2

The air gap technique reduces the amount of scatter radiation reaching the IR because A. more scatter is absorbed in the air B. less scatter is produced in the patient C. more scatter misses the IR D. less scatter misses the IR

C. more scatter misses the IR

When the x-ray beam is not lined up with the center of the grid you have _________ cutoff. A. upside-down focused B. off-level C. off-center D. off-focus

C. off-center

The field shape produced by a collimator is A. round B. oval C. rectangular D. all of the above

C. rectangular

Linear grids are the most commonly used because A. they are very inexpensive B. the tube can be angled in all directions C. the tube can be angled in the direction of the lead lines D. all of the above

C. the tube can be angled in the direction of the lead lines

The two major factors that affect the amount of scatter radiation produced and exiting the patient are A. kVp and mAs B. volume of tissue irradiated and mAs C. volume of tissue irradiated and kVp D. kVp and the use of a grid

C. volume of tissue irradiated and kVp

How can a linear grid be used?

Can only angle along direction of grid lines

What interaction primarily produces scatter?

Compton 90%

What is the result when you increase your grid ratio?

Contrast increase Patient dose increase likelihood of grid cutoff increases

Which of the following grids provides excellent scatter clean-up but requires close to perfect alignment to avoid cutoff? A. 5:1 ratio grid. B. 8:1 ratio grid. C. 12:1 ratio grid. D. 16:1 ratio grid.

D. 16:1 ratio grid.

If 22 mAs and a 5:1 grid results in an excellent radiograph, how much mAs is needed with a 12:1 grid? A. 8.8 mAs. B. 9.2 mAs. C. 52.8 mAs. D. 55 mAs.

D. 55 mAs.

During the exposure, the grid in the bucky A. reciprocates B. moves slightly from side to side C. moves slightly from top to bottom D. A and B E. A and C

D. A and B

A grid with lead strips that run parallel to each other is a A. parallel grid B. focused grid C. nonfocused grid D. A and C E. B and C

D. A and C

Restriction of the primary beam to the anatomy of interest A. reduces patient exposure B. is a major cause of repeated images C. reduces the amount of scatter produced D. A and C E. B and C

D. A and C

The Moiré effect can be caused by A. using a grid with a frequency similar to the CR laser scanning frequency B. using a focused grid upside down in the bucky C. using a grid cassette in the bucky D. A and C E. B and C

D. A and C

Which of the following factors need to be considered when determining the grid to be used for a specific examination? A. Patient exposure. B. Level of contrast improvement needed. C. Focal range. D. All of the above.

D. All of the above.

Which of the following produces the greatest amount of scatter radiation exiting the patient? A. Low kVp and small field size. B. Low kVp and large field size. C. High kVp and small field size. D. High kVp and large field size.

D. High kVp and large field size.

Grid cutoff results in A. reduced exposure to the IR B. a light film-screen image C. possible quantum mottle D. all of the above

D. all of the above

The volume of tissue irradiated is determined by A. the area of collimation B. patient thickness C. field size D. all of the above

D. all of the above

The automatic collimator A. automatically collimates to the anatomy of interest B. is required by law on all new equipment C. is seldom found on modern x-ray equipment D. automatically collimates to the IR size

D. automatically collimates to the IR size

The recommended SIDs that can be used with a focused grid is the A. convergent line B. focal distance C. convergent point D. focal range

D. focal range

An IR that has a grid permanently attached to its front surface is a A. wafer grid B. bucky C. grid cap D. grid cassette

D. grid cassette

To determine the amount of mAs to be increased when making grid changes, it is necessary to use the GCF, also known as the A. grid constancy figure B. grid compensatory factor C. general compensation factuals D. grid conversion factor

D. grid conversion factor

When the SID is above or below the focal range you have _________ cutoff. A. upside-down focused B. off-level C. off-center D. off-focus

D. off-focus

Grids absorb scatter radiation because the scattered photons A. have high energy B. have extremely low energy C. travel in the same direction as the transmitted photons D. travel at an angle to the transmitted photons

D. travel at an angle to the transmitted photons

The Moiré effect is also known as the _________ pattern. A. cheetah B. giraffe C. lion D. zebra

D. zebra

A linear grid A. has lead strips that cross each other B. has lead strips that travel in one direction C. is the most common type of radiographic grid D. A and C E. B and C

E. B and C

NEED TO KNOW!! True or False Grids effect the production of radiation.

False

NEED TO KNOW!! What causes a narrow band of normal density?

Focused Grid Upside Down

Who invented the grid and when?

Gustav Bucky in 1913

What frequency grid is particularly important for digital radiography systems? Why?

High frequency grid to avoid aliasing artifacts low frequency grids can also be used

Higher kVp - ___________ interactions - amount of scatter hitting IR ____________

Higher kVp - fewer interactions - amount of scatter hitting IR increases

Higher kVp = _________ image contrast

Higher kVp = Lower image contrast

Who invented the moving grid and when?

Hollis Potter in 1920

If air gap technique is used in place of a grid patient dose is ___________ by the ____________

If air gap technique is used in place of a grid patient dose is decreases by the grid factor.

What is a long dimension grid?

Lead strips run parallel to long axis Need to center to grid cross wise, but can angle to it length wise - Portable chest length wise - Decubs cross wise

What are short dimension grids?

Lead strips run parallel to short axis Need to center to grid length wise, but can angle to it cross wise - Portable chest cross wise - X-T lateral L-spine - Decubs length wise

Light field and______________________ must be symmetrical.

Light field and radiation field must be symmetrical.

LD

Long dimension grids

Lower kVp = ___________ image contrast

Lower kVp = Higher image contrast

What do you get with a higher kVp?

More even penetration of all tissues (Reducing subject & image contrast) More scatter hitting the IR with more energy (Reducing image contrast)

How is the air gap technique set up?

OID is increased 5 to 10 inches requires a longer SID - for every 1" air gap; SID must be increased 12" mAs must be adjusted to compensate for increased SID (inverse square law)

NEED TO KNOW!! What can cause grid cut off along one side?

Off level Off center Angling across the grid lines

NEED TO KNOW!! What does an increase in collimation cause?

Patient dose decreases Scatter radiation decreases. Radiographic contrast increases. Quantum noise increases.

NEED TO KNOW!! What does an increased field size cause?

Patient dose increases. Scatter radiation increases. Radiographic contrast decreases. Quantum noise decreases.

How does a higher kVp effect the different interactions?

Photoelectric interactions decrease drastically Compton interactions very slightly decrease (scatter produced has more energy and more likely to hit IR)

PBL

Positive Beam Limitation

What is another name for automatic collimators?

Positive Beam Limitation (PBL)

SD

Short dimension grids

The collimator has to be within ________________________________.

The collimator has to be within 1 degree of perpendicular or less.

The collimator misalignment has to be less than _______ of SID.

The collimator misalignment has to be less than 2% of SID.

The higher the efficiency the ________ scatter is absorbed and ________ radiation hits the IR.

The higher the efficiency the more scatter is absorbed and less radiation hits the IR.

The higher the grid ratio the _________ potential for cutoff.

The higher the grid ratio the more potential for cutoff.

How does tissue volume effect scatter?

Thicker tissue produces more scatter (Fat produces more scatter than same thickness of muscle) Larger field size produces more scatter

What causes grid focus de-centering error?

Wrong SID

What is grid cutoff?

a decrease in the number of transmitted photons reaching the IR because of some misalignment of the grid. - Cutting them off from IR - Results increase in noise caused by a decrease in x-ray photons reaching the digital IR.

NEED TO KNOW!! What is the function of a grid?

absorb scatter radiation

When does a linear grid non-focused grid work the best?

at longer SID & smaller IR (FOV)

What is another name for grid conversion factor?

bucky factor

How does bowing caused by patient's weight cause artifacts?

changes canting of grid lines

What is tissue volume?

determined by part thickness and field size (collimation)

GCF

grid conversion factor

What is another name for grid frequency?

grid density

NEED TO KNOW!! What is grid lead content affected by?

grid frequency and ratio The higher the lead content the more efficient the scatter clean up

How are grid lines arranged in a linear grid focused grid?

grid lines are canted (angled) to match divergent rays within a specified SID focal range

How can dropping a grid cause artifacts?

grid lines out of alignment show up on image

What is the grid ratio formula?

grid ratio = height/width of interspace

What is grid ratio?

height of the Pb strip to the width of the interspace (material)

When is it recommended that a grid be used?

if part thickness is 10 cm or more 70 kVp or more is used (some books are saying 60 kVp)

NEED TO KNOW!! What is the purpose of a grid?

increase image contrast

How do you compensate when going from a 14x17 to a 8x10?

increase mAs by 50%

NEED TO KNOW!! What is the affect of increased grid frequency when given the same grid ratio?

lead content decreases - width (thickness) of leads strips gets thinner to get more lines in - less lead content, less scatter absorbed, less efficient - higher grid frequency, lower contrast

NEED TO KNOW!! What is the affect of increased grid ratio when given the same grid frequency?

lead content increases - leads strips gets taller - more lead content, more scatter absorbed, more efficient - higher grid ratio, higher contrast

What are the types of grid patterns?

linear grid (parallel grid) Cross-hatched grid

How do you compensate when going from a 14x17 to a 10x12?

no change

If grid is added and technique is NOT adjusted, what is the change in patient dose?

no change in patient dose

What are the types of linear grids?

non-focused grid focused grid

What is grid frequency?

number of grid line (Pb strips) per mm or inch

NEED TO KNOW!! what is the Grid factor formula?

old mAs/new mAs = old grid factor/new grid factor

If grid is added and technique is adjusted, what will happen to patient dose?

patient dose will increase

What does scatter do?

reduces image contrast and increases dose/exit or remnant radiation

What is a virtual grid?

software program that reduces the signal energy that response to the scatter, which increases image contrast

What is Moire effect or aliasing?

the sampled signals contain frequencies that are sampled at less than 2 samples / cycle, then the computer system assigns a lower frequency signal than the actual frequency signal. The assigned frequency represents an aliased signal in the output image.

What is a grid made of?

thin strips (lines) of lead with radiolucent material between (inter-space)

Why does the SID have to be increased with the air gap technique?

to minimize magnification and maintain detail

What is the purpose of the air gap technique?

used instead of a grid to reduce the amount of scatter reaching the IR

What is the grid conversion factor?

used to determine the adjustment in mAs needed when changing from using a grid to non-grid (or vice-versa) or for changing to grids with different grid ratios.

When are medium and high frequency grids used?

used with stationary grid holders (e.g., portable radiography and many digital radiography systems)

NEED TO KNOW!! How are the grid lines arranged in a linear grid non-focused grid?

vertical or parallel to each other

What does the amount of scatter produced depend on?

volume of tissue exposed kVp used

When can cross-hatched grid pattern be used?

when the tube can not be angled Fluoroscopy & C-arms

When are low frequency grids used?

with systems having a moving grid assembly (Bucky device) that oscillates during the exposure to blur the grid lines