P9 - Scatter Control and Filtration

- High kVp

- Thick tissue-dense body part

- Large x-ray field size (collimation)

State the factors controlling scatter

- Make less scatter radiation

- Prevent scatter photons from reaching the film

State the scatter control strategies

Collimation

_____ is used to restrict the size and shape of the x-ray beam and to reduce patient exposure

Increase mAs for more thickness

Patient thickness effect on factor selection

Compression devices

_____ also help decrease tissue thickness

Grid

A _____ goes between the patient and film

- Post-patient scatter reduction

- Increases patient dose, but makes a better image

Increase mAs

When we use a grid, what do we adjust?

Decreased

How do grids affect density?

Higher contrast

How do grids affect contrast?

Increase, lines on image

How do grids affect artifacts?

- 12:1

- 100 lines/inch (minimum)

- Focal range 40-72"

- Linear

- Focused

- Stationary

State the recommended grid

Between patient and film

Where does the grid go?

12:1

Recommendaed grid ratio (line pairs per mm)

Lines per inch

Grid frequency

<90

_____ lines per inch results in distracting lines

>100

_____ lines per inch results in faint lines (tolerable)

Linear

Which grid pattern do we want?

Focused

Which grid pattern do we want?

Off-level

This is an _____ grid

Off-center

This is an _____ grid

Off-focus

This is an _____ grid

Upside-down

This is an _____ grid

60%

The introduction of 1 mm of aluminum filtration reduces the skin dosage by _____

80%, 70%

2 mm of aluminum reduces skin dosage by _____ at 50Kv and _____ at 100 kV

Filtration

_____ changes beam quality and quantity

- Patient exposure

- Image quality

- Inherent

- Added

- Compensating

State the types of filtration

Total

Inherent filtration + added filtration = _____ filtration

- 2.5 mm aluminum equivalent

Inherent

_____ filtration: total of about 0.5 mm aluminum equivalent

- Tube

• Glass envelope

• Oil

Added

_____ filtration: total of about 2 mm aluminum equivalent

- Added aluminum between the collimator and the tube

- Collimator mirror

Beam hardening

Weaker photons preferentially removed

Decreases

Beam hardening _____ beam quantity

Increases

Beam hardening _____ beam quality

Half-value layer (HVL)

- Thickness of material required to attenuate 1/2 the photons in the beam

- Permits equivalency of different materials

12.5%

- First HVL removes 50% of initial photons

- Second HVL removes 50% of what's left

- Third HVL removes 50% of what's left

What percentage of beam remains after 3 HVL's?

Compensating filters

- Applied by technician when setting up for exposure

- Composed of:

• Aluminum

• Copper

• Rare earth metals

- Used to compensate for various tissue thicknesses

• Thoracic spine

• Foot

• Shoulder (AC joint)