Radiographic Contrast

Define Contrast

the difference between adjacent densities

5 ways to describe high contrast

• few shades of gray

• increased contrast

• low kVp

• short scale

• less latitude

5 ways to describe low contrast

• many shades of gray

• decreased contrast

• high kVp

• long scale

• greater latitude

Does this radiograph have good or bad technique?

good

Does this radiograph have high or low contrast?

high

Does this radiograph have high or low contrast?

low

What are the two types of contrast?

• Image Receptor (Film) Contrast

• Subject Contrast

The range of densities that the image receptor is capable of recording is determined by:

1) Intensifying Screens

2) Film Density

3) D log E curve

4) Processing

Intensifying screens create an inherently _____ contrast image.

The higher the speed of the screen, the ____ the contrast.

BUT, this difference is ______.

higher

greater

negligible

Within the diagnostic range, film density has ____ effect on contrast.

BUT, excessive or inadequate density _____ contrast.

little

decreases

What represents the physical composition of the film?

D log E curve

D log E Curve

The steeper (more vertical) the slope of the curve, the ______ contrast.

The steeper the slope, the _____ the range of exposures that will produce densities within the diagnostic range.

The greater the contrast, the ____ the latitude.

greater

narrower

less

Which film has greater contrast, greater latitude, greater speed, and less detail?

film A

List the 4 processing factors that affect contrast

1. developer time

2. developer temperature

3. replenishment rate

4. contamination of the chemicals

Changes in any of the processing factors will result in ___ contrast on the film.

decreased

(Subject Contrast) The range of difference in the intensity of the x-ray beam after it has passed through the patient is dependent upon:

1. kVp

2. amount and type of irradiated material

What is the primary controller of subject contrast?

kVp

The higher the kVp, the ___ the range of energies in the beam.

This produces a ____ range of densities on the film (____).

greater

wider, (grays)

High kVp = ___ contrast

low contrast

With low kVp, dense structures (bone) will absorb most of the x-rays while x-rays will pass through structures with ____ density (soft tissue or air).

Low kVp will ____ differential absorption.

little

enhance

Low kVp = ____ contrast

high contrast

Define the Compton Effect

higher kVp will cause more scatter

(T/F) Scatter causes fog on the film.

true

What is fog?

What will fog do to contrast?

an overall unwanted density on the film

any kind of fog will decrease contrast

The thicker the body part, the ____ x-rays are absorbed and the ____ x-rays are transmitted.

Smaller body parts absorb ____ x-rays.

Great difference in adjacent body part thicknesses will cause ____ subject contrast.

more, less

less

high

(T/F) When the overall thickness of the body part increases or the field size increases, the amount of scatter decreases.

False, the amount of scatter increases

More scatter = ____ contrast

less contrast

Two factors that affect subject contrast:

1) atomic number

2) density (mass per volume)

The higher the atomic number, the ____ x-rays are absorbed.

The greater the difference in average atomic number of adjacent tissues, the _____ the contrast.

Barium = Soft tissue =

more

greater

56, 8

The greater the density of a tissue, the ____ x-rays are absorbed.

When the difference between adjacent densities is great, the subject contrast is ____.

Bone vs. ____ tissue

more

high

lung

What is the major controller of radiographic contrast?

kVp

An increase in kVp will cause a ____ in contrast.

decrease

It takes a change of at least ___% in kVp to see a visible difference in contrast.

4%

mAs controls _____

density

If the density is too much or too little, the contrast is _____.

reduced

What affect does focal spot size have on contrast?

little or no effect

What effect does anode heel effect have on contrast?

very little effect

What does SID affect?

density

OIDs over ____” will reduce the amount

less scatter = ____ contrast

10 inches

higher

more filtration = ____ contrast

less contrast

tighter collimation (increased beam restriction) will result in ____ scatter

less scatter = ____ contrast

less

higher

the thicker the part, the _____ scatter

more scatter = ____ contrast

higher the atomic number of the part = the ____ the contrast

more

less

higher

Grids absorb scatter which creates ____ contrast

higher contrast

What is the contrast improvement Factor (K)

K = average gradient w/grid/average gradient w/o grid

Most grids have contrast improvement factors between ____ and ____.

the contrast is ___ to ___ times higher than if a grid is not used.

the higher the contrast improvement factor —- the _____ the contrast

1.5 and 3.5

1.5 to 3.5

higher

screens create _____ contrast

the faster the screens, the _____ the contrast

higher

higher

Changes in temperature, developer times, replenishment rate, or chemical contamination will ____ contrast

decrease