MOD 2: CONTRAST

• Factors affecting radiographic contrast:

  1. kVp

  2. Grid

  3. Beam Restriction

  4. Subject Contrast

  5. Compression

  6. Air Gap Technique
• Kilovoltage peak (kVp) is the primary technical factor for controlling radiographic contrast
• High kVp:

  • High frequency
  • High energy
  • Hard x-rays
  • Short Wavelength
  • Produces more scatter radiation, resulting in low contrast resolution
  • Compton effect is more prominent
  • X-ray beam is highly penetrating
• Radiographic Grid:

  • Designed to absorb scatter radiation before it reaches the recording medium
  • Placed between the patient and the image receptor
• Beam Restriction:

  • A larger field size increases the amount of tissue irradiated, causing more scatter radiation
  • Collimation affects radiographic contrast, especially in large anatomic areas and with high kVp
• Aperture Diaphragm is the simplest beam-restricting device, with a lead or lead-lined aperture that cannot be adjusted from the designed size
• Cones and cylinders limit unsharpness surrounding the radiographic image more than aperture diaphragms
• Object to Image Receptor Distance (Air Gap Technique):

  • Creating distance between the object and IR decreases beam intensity
  • Air gap technique reduces scatter radiation reaching the IR, increasing radiographic contrast
• Part Thickness:

  • Affects the amount of x-ray beam attenuation
  • Thick parts absorb more radiation, thin parts transmit more radiation
• Filtration:

  • Reduces low-energy photons in the x-ray beam
  • Inherent filtration includes the tube envelope, oil, and window in the tube housing
• Factors affecting radiographic contrast:

  1. kVp

  2. Grid

  3. Beam Restriction

  4. Subject Contrast

  5. Compression

  6. Air Gap Technique
• Kilovoltage peak (kVp) is the primary technical factor for controlling radiographic contrast, affecting both x-ray quality and quantity
• High kVp produces more scatter radiation, resulting in low contrast resolution, while low kVp produces less scatter radiation, resulting in high contrast resolution
• Radiographic grid:

  • Designed to absorb scatter radiation before it reaches the recording medium
  • Placed between the patient and the image receptor
  • Reduces the number of scatter rays striking the film
• Beam Restriction:

  • Any change in the size of the x-ray field alters the amount of tissue irradiated
  • Larger field size increases tissue irradiated, causing more scatter radiation and less radiographic contrast
• Aperture Diaphragm is the simplest beam-restricting device, with a lead or lead-lined aperture that cannot be adjusted from the designed size
• Cones and cylinders limit unsharpness surrounding the radiographic image more than aperture diaphragms, with cylinders better at reducing image unsharpness than cones
• Object to Image Receptor Distance (Air Gap Technique):

  • Creating distance between the object and IR decreases beam intensity
  • Air gap technique reduces scatter radiation reaching the IR, increasing radiographic contrast
• Part Thickness:

  • The thickness of the anatomic part being imaged affects the amount of x-ray beam attenuation
  • Thick parts absorb more radiation, thin parts transmit more radiation
• Filtration:

  • Filtration is added to the x-ray beam to attenuate or absorb low-energy photons
  • Main function of filtration is to absorb low-energy photons that only contribute to patient dose
• 1. ray Tube Filtration:

  • Increasing tube filtration increases the ratio of higher-penetrating x-rays to lower-penetrating x-rays
  • Added filtration increases the average energy of the x-ray beam with a reduction in x-ray quantity
• Inherent filtration refers to the filtration permanently in the path of the x-ray beam, including the envelope of the tube, the oil surrounding the tube, and the window in the tube housing