***Control of Scatter (Test 2)

Remnant Radiation (direct transmission)

What is the good radiation that forms the radiographic image and passes through the patient without any interactions?

Compton Scatter

What is the bad radiation that hits a structure and changes direction?

Image contrast

What refers to the visible difference between the signal intensity (dark and light areas) of the image (post-processing)?

Subject Contrast

What refers to the different shades of gray due to differential absorption of the radiation within the body tissues (patient factors)?

Contrast Resolution

What refers to the ability to image and distinguish soft tissues?

Image contrast decreases

As scatter radiation increases, what happens to image contrast?

Subject contrast decreases

As scatter radiation increases, what happens to subject contrast?

Contrast resolution decreases

As scatter radiation increases, what happens to the overall contrast resolution?

Technologist dose increases

As scatter radiation increases, what happens to the technologist's dose?

99%

What percent of the technologist dose comes from scatter radiation?

PE absorption decreases

As kVp increases, what happens to photoelectric absorption (PE)?

Patient absorbed dose decreases

As the KVP increases and PE absorption decreases, what happens to the patient's absorbed dose?

Compton scatter increases

As the kVp increases, what happens to Compton scatter due to increased penetration?

Contrast resolution decreases

As the kVp increases, what happens to contrast resolution due to increased Compton scatter?

IR exposure increased

As kVp increases, what happens to image receptor exposure (15% rule)?

Increase kVp

As body part thickness increases, what must increase to penetrate the patient's tissues?

Scatter production increases

As body part thickness increases, what happens to scatter production?

Contrast decreases

As body part thickness increases, what happens to contrast due to increased scatter production?

Post-processing and dynamic range

In digital imaging, what corrects the issue of scatter on an image?

IR exposure decreases

As body part thickness increases, what happens to IR exposure due to increased absorption in the patient?

Compression bands and turning the patient prone

What two things are done to decrease patient thickness?

Patient exposure increases

If the field size is increased, what happens to patient exposure?

Scatter radiation increases

If the field size is increased, what happens to scatter radiation?

Contrast resolution decreases

If the field size is increased, what happens to contrast resolution due to the increased scatter?

Image contrast increases, IR exposure decreases, and patient exposure decreases

If the field size is decreased, what happens to image contrast, IR exposure, and patient exposure?

Decrease kVp and decrease field size

To reduce the production of scatter, what must be done?

Reduced patient exposure

If the field size is reduced or the beam restriction is increased, what effect does this have on the patient's exposure?

Using beam restriction

What is the best way to decrease patient exposure?

Reduced scatter production

If the field size is reduced or the beam restriction is increased, what effect does this have on the production of scatter?

Reduced IR exposure

If the field size is reduced or the beam restriction is increased, what effect does this have on the IR exposure?

Increased image contrast

If the field size is reduced or the beam restriction is increased, what effect does this have on the image contrast?

Increased visibility

If the field size is reduced or the beam restriction is increased, what effect does this have on the visibility of the image?

Aperture Diaphragm

What is the oldest and simplest type of beam restriction device that has lead with a hole in the center of it?

1 cm smaller

When using an armature diaphragm, the field size must be how much smaller than the film size?

Cones (flared) and cylinders (straight)

What type of beam restriction device is made of heavy metal that extends in length to restrict the beam size?

Circular images

What kind of images did cones and cylinders produce?

Variable Collimator

What is the most common beam restriction device that has an infinite number of field sizes, 2 sets of shutters, light localization, and a visual indication of field size?

Absorbs off-focus radiation

What does the top set of shutters do in the variable collimator?

Makes edges of the beam sharp

What does the bottom set of shutters do in the variable collimator?

Positive Beam Limitation (PBL)

What was a regulation mandated by the FDA from 1974 to 1994 that X-ray equipment automatically adjusts the X-ray beam to the size of the selected image receptor?

To reduce scatter radiation reaching the IR

What is the purpose of grids?

Grids absorb scatter and some remnant radiation

Why do grids require increased technique?

Image contrast increases

If a grid reduces scatter radiation that reaches the IR, what happens to image contrast?

Visibility increases

If a grid reduces scatter radiation that reaches the IR, what happens to the image's visibility?

Spatial resolution, magnification, and distortion

What do grids not affect?

Patient absorbed dose and ESE increases

When using a grid and the technique is properly adjusted, what happens to the patient's absorbed dose and entrance skin exposure?

IR exposure decreases

If the grid ratio increases and there are no technical adjustments, what happens to the IR exposure?

Patient absorbed dose and ESE do not change

If the grid ratio increases and there are no technical adjustments, what happens to the patient's absorbed dose and entrance skin exposure?

Stationary Grids

What type of grid is configured in a cross-hatch pattern of lead strips that runs in both directions and was invented by Gustav Bucky in 1913?

Made them moveable to blur out grid lines

In 1920, what did Hollis Potter do to the stationary grid?

Interspace distance

What is the distance between the grid strips?

radiolucent

Interspace material is ____________

Plastic fiber

What is the interspace material made of?

Hold the lead grid strips in a precise position

What is the interspace material designed to do in the grid?

Allows remnant radiation to pass through

Because the interspace material in a grid is radiolucent, what does this allow?

lead / radiopaque

Grid strip material is made of _______ and is ___________

- It's inexpensive

- It's easy to shape

- Has a high atomic number

What are the three reasons that lead is the material of choice for grid strips?

To provide stability and keep out moisture

Why is the entire grid covered by a thin sheet of aluminum?

Because scatter is at an angle

Why is scatter radiation more likely to be absorbed by the lead grid strips?

Grid Ratio

What refers to the ratio of the height of the lead strips and the distance between the strips?

R = h/D

What is the grid ratio formula?

Grid efficiency increases

As the grid ratio increases, what happens to the efficiency of the grid?

Used at specific SIDs

With higher grid ratios, how should they be used?

- Thicker lead strips and keep interspace thickness the same

- Thinner interspace and keep lead strip thickness the same (allows more lead strips)

- Increase the height of the lead strip

What are the three ways the manufacturer can increase the grid ratio?

Make the lead lines more visible

All of the ways to increase the grid ratio do what to the lead lines in the grid?

Grid frequency

What refers to the number of lead lines per centimeter?

25 - 45 lines/cm

What is the normal grid frequency for most grids?

- Decrease the interspace thickness

- Decrease the lead strip thickness

What are the two ways a manufacturer can increase the frequency of a grid?

Increased grid ratio and patient dose

What does decreasing the interspace thickness result in?

Decreased grid ratio and scatter absorption

What does decreasing the lead strip thickness result in?

Grid Ratio

What is the most frequently used method of checking the efficiency of a grid?

Contrast Improvement Factor (K): The ratio of contrast with a grid to contrast without a grid

What refers to how well contrast is improved with the use of a grid? What is another definition?

K = contrast with a grid / contrast without a grid

What is the formula for the contrast improvement factor?

1.5 to 2.5

What is the normal contrast improvement factor (K)?

K depends on how the grid ratio is affected

What does the contrast improvement factor (k) depend on?

K increases

If the grid ratio increases, what happens to the contrast improvement factor (k)?

K decreases

If the lead strip thickness is decreased or made thinner to increase the grid frequency, what happens to the contrast improvement factor (K)?

K increases

If the interspace thickness is decreased or made thinner to increase the grid frequency, what happens to the contrast improvement factor (K)?

Bucky Factor (B) or Grid Factor

What measures how much the technique will have to be increased compared to a non-grid exposure?

- B = Incident remnant rad. reaching grid /Transmitted - image forming rays

- B = Patient dose with a grid / Patient dose without a grid

What are the two Bucky factor (b) formulas?

B increases

If the grid ratio increases with the proper technical adjustments, what happens to the bucky factor (B)?

B increases

If the kVp increases, what happens to the bucky factor (b)?

Patient exposure increases

If the bucky factor increases, what happens to the patient's exposure?

Cross-Hatched Grid

What type of grid had lead strips that ran in two directions and was very efficient in stopping scatter before it reached the IR?

- Can't angle tube

- Centering must be exact

- Requires much higher exposures

What are the three disadvantages of a cross-hatched grid?

Parallel or linear unfocused grid

What type of grid has lead strips running in one direction and always has grid cutoff on the lateral borders due to not matching diverging x-ray photons?

With high grid ratios, large field sizes, and short SIDs

With parallel/linear unfocused grids, when would grid cutoff be more noticeable?

Linear Focused Grid

What type of grid is the most common and has lead strips that run in one direction but are canted (angled) to the beam's path?

Certain SIDs called the focal distance or focusing distance

What must be used specifically with linear focused grids?

Less positioning latitude

When using linear focused grids, what was needed less with high ratio grids?

Linear focused

Moving grids are almost always ___________ __________

Reciprocating and Oscillating

What are the two types of movements a moving grid can have?

Reciprocating

What type of moving grid is motor-driven in a back-and-forth motion?

Moves perpendicular to the grid lines

How does the reciprocating motion in a moving grid move with the grid lines?

Oscillating

What type of moving grid is an electromagnetic device that causes the grid to move in a circle?

Needs minimal OID and can run roughly

What are two disadvantages of a moving grid?

Virtual Grid Software

What type of grid is the latest innovation for scatter/contrast improvement in digital imaging, which uses computer algorithms to identify the energy of the X-ray beam and the frequency of scatter radiation, thereby eliminating the scatter frequency in the reconstructed image?

FugiFilm in 2014

Who created the virtual grid software?

Reduces patient radiation dose, improves image contrast, and is easier to use

What are the three advantages of virtual grid software?

Grid Cutoff

What is described as the absorption of the remnant beam caused by a misalignment of the radiographic grid?