1. Radiographic Contrast

2. Contrast
The range of density variation among the light and dark areas on a radiographic image.
A difference in density on adjacent anatomic structures.

3. Radiographic Contrast
The overall contrast of a radiograph
Dependent on two factors.
Subject contrast
Film contrast

4. Subject Contrast The contrast in the aerial image.
The ratio of the number photons in two or more equal zones of the aerial image.
Aerial Image = The image that contains the information derived from the patient.

5. Aerial Image
Also contaminated by unwanted noise which impairs the quality of information that is displayed on the imaging system.
Noise factors
Quantum mottle
Scattered radiation
Fogging

6. Determining Factors of Subject Contrast
Patient Size
Density
Attenuating characteristics of the subject.

7. Determining Factors of Subject Contrast
Patient Size (thickness)
With increased total thickness of tissue traversed by the x-ray beam, there are more atoms available for interactions (absorption and scatter).
Greater attenuation means that less radiation is transmitted through the patient; less exit radiation is available for interaction with the imaging system.

8. Determining Factors of Subject Contrast
Part density
An increase in density (grams/cm3) increases x-ray attenuation per cm of tissue.
With higher density, more electrons are present per cm3 of tissue to engage in Compton’s scatter.

9. Determining Factors of Subject Contrast
Attenuating characteristics of the subject.
Photoelectric absorption increases dramatically with increasing atomic number.
Attenuation is higher per cm of bone than per soft tissue.

10. Film Contrast
Films vary in inherent contrast, depending on their emulsion characteristics.
Films are designed for long, medium, and short contrast.
Film development also affects film contrast.

11. Film Contrast
Intensifying screens convert 98% or more of the radiologic image to light.
The aerial image is changed almost completely to a light image, which is then recorded by the film.
This process enhances the contrast because screen type film has more inherent contrast for the light emitted by the screens than for x-rays directly.

12. Film and Subject contrast relationship
Radiopacity is the degree of attenuation in a tissue.
Radiolucency is the degree of transmission in a tissue.
The greater the tissue attenuation, less radiation transmitted through the patient.

13. Film and Subject contrast relationship
Various soft tissues are represented as shades of gray, depending on their differential absorption/attenuation.
Fat capsule around the kidneys.
Fat around the psoas muscles.
Both appear as dark gray or nearly black lines.
This ultimately produces subject contrast which improves the image quality.

14. Controlling factors Kilovoltage (kVp)
Determines the penetrability of the remnant beam.
As the penetrability increases, the scale of contrast on the radiographic image lengthens thus giving the appearance of an increase in the number of gray shades.

15. Controlling factors
Likewise, as the penetrability of the remnant beam decreases, the scale of contrast shortens thus giving the image a more black and white appearance.

16. Influencing Factors Milliampere seconds (mAs) Grids
Beam Limiting Devices
Intensification Factor
Patient Considerations
Contrast Media

17. References
Bushong, S. Radiologic Science for Technologists, Physics, Biology, and Protection, 6th Edition, Mosby, 1997.
Bushberg, et al. The Essential Physics of Medical Imaging, Williams & Wilkins, 1994.
Carlton et al. Principles of Radiographic Imaging an Art and a Science, 3rd Edition, Delmar, 2001.
Selman, J. The Fundamentals of X-Ray and Radium Physics, 8th Edition, Charles Thomas, 1994.