Radiology 1 PP

• Electromagnetic radiation


  Energy that travels in a straight path through space in waves
• 1. rays


  • Short wavelength, high energy radiation
• Physical Properties of X-rays

  1. X-rays travel in a straight line

  2. X-rays have enough energy to pass through many materials (transmitted x-rays)

  3. As x-rays pass through materials they will collide with electrons

  4. Change the path of the x-ray (scatter radiation)

  5. Increase electron energy (excitation)

  6. Certain substances will then release the energy in the form of light (fluorescence)

  7. Ejects an outer electron from atom (ionization)
• 1. ray tube


  • Glass vacuum tube
  • Cathode and anode produce X-rays
  • Metal housing
  • Protects the glass tube
  • Oil for cooling
  • Window and filter where X-rays exit
• Cathode


  • Electron source
  • Tungsten filaments
  • Similar to light bulb
  • Emit electrons rather than light
  • Focusing cups
  • Direct electrons toward the anode
• Anode


  • Tungsten metal target
  • Electron strikes release: X-rays (1% of energy), Heat (99% of energy)
  • Beveled surface
  • Directs X-rays downward through housing window
• Stationary anode


  • Tungsten target mounted on a stationary copper base
  • Focal spot prone to overheating and damage
  • Can only produce low energy X-rays

  •Dental radiography

  •Portable radiography
• Rotating anode

  • Target is a rotating disc with a beveled edge
  • Heat distributed over larger area
  • Can produce higher energy X-rays

  •Can produce higher energy X-rays

  •Small animal radiography

  •Large animal clinics
• Collimator


  • Controls the size of the primary x-ray beam
  • Reduce exposure to patient and personnel
  • Minimize scatter and improves image quality
• Collimator types


  • Adjustable lead shutters
  • Lead cones
• Tube Stand


  • Supports the x-ray tube and collimator
  • Adjustable: Tube height, Tube angle, Moves left/right along table
• Cassette Tray and Storage Bin

  • Holds x-ray film cassette under table
  • Tray lock
  • Aligns tray and x-ray tube
  • Moves tray left/right with tube stand
  • Can be unlocked for independent movement
  • Lead lined storage bin for loaded cassettes
• Control Panel


  • On/off switch
  • Kilovolt selectors
  • Milliamp selector
  • Time selector
  • Newer machines don't have this
  • Exposure foot switch
• Hazards of Ionizing Radiation

  • Damage to rapidly dividing or sensitive cells: Hematopoietic and lymphatic tissue, Intestinal epithelium, Gonads, Thyroid, Bone, Skin, Developing embryos
  • Pregnant technicians should NOT be taking radiographs
• Maximum Permissible Dose


  • National Council on Radiation Protection & Measurements (NCRP) determines the maximum exposure dose per year
  • Permissible dose for professionals is higher than for the general public
  • Professionals are trained and monitored regularly
• Units of measurement


  • Sieverts or rems
  • Adjusts for the biological effects of different radiation strengths
• ALARA (As Low As is Reasonably Achievable)


  Every effort should be made to keep the exposure rates as far below the dose limits as possible
• Exposure Allowances


  • 0.001 Sv/week (0.1 rems/Week)
  • 0.0125 Sv/quarter (1.25 rems/Quarter)
  • 0.05 Sv/year (5.0 rems/Year)
• Dosimetry


  • Dosimeter: Device that measures radiation exposure
  • Film badge most common
  • Must be worn at all times during radiography
  • Clip to collar outside of apron (required by California law)
  • Reports issued quarterly: Includes quarterly, annual, and lifetime exposure
• Primary beam


  1. rays intended to penetrate the patient and produce an image
• Filtration


  Aluminum filter eliminates weak x-rays that do not help produce an image but can still cause tissue damage
• Collimation


  Restricts the size of the beam to the minimum needed for the radiograph
• Technicians' body parts should never be in the primary beam
• Secondary radiation (aka scatter radiation)


  Scatter from the patient, table, or anything else in the primary beam
• Only essential personnel allowed in the room during radiography
• Use chemical restraint or mechanical restraint devices when possible
• Stand upright and away from the patient when using manual restraint
• Always wear protective apparel
• mAs


  • Milliamperes
  • Determines the quantity of x-rays produced per second
• Small animal x-ray machines have two settings

  • 100 mA
  • 300 mA
• mAs


  • milliamperes x seconds
  • The total quantity of x-rays produced during an exposure
• kVp


  • Kilovolt peak
  • The strength of the x-rays produced during an exposure
  • Thicker tissues require more powerful x-rays
  • Larger patients require higher kVp settings
  • Patient thickness is measured with a caliper
• kVp vs mAs


  • kVp is the power/strength/quality of the x-ray beam. Impacts both density and contrast
  • mA is the quantity/number of x-rays. Impacts the density
  • Time (seconds) impacts the density. Shortest time = less exposure and less movement of patient
• Distance


  • Source-image distance (SID): Distance between any x-ray source and any type of receptor (film, digital sensor, fluoroscope, etc)
  • Focal film distance (FFD): Distance between the anode focal spot and the x-ray film
  • mAs and kVp are determined for a specific distance
  • SID is typically 40 inches in small animal radiology
• Inverse square law


  • The intensity of the x-ray beam is inversely related to the square of the source-image distance (SID)
  • Double the distance, the beam intensity is reduced to 1/4
  • Halve the distance, the beam intensity increases 4 fold
  • Triple the distance, the beam intensity is reduced to 1/9
• Scatter


  • Scatter radiation is released in random directions
  • Exposure hazard to patient and technicians
  • Exposes the film and reduces image clarity
  • Exposes the film outside of the collimation area
  • Increased scatter: Large patients, Poor collimation, High kVp
• Grids


  • Device positioned between patient and film to absorb scatter radiation
  • Vertical strips of lead or aluminum and spacer material
  • Mounted under the table and above the cassette tray
• Motion


  • Patient positioning: Veterinary patients don't want to stay still in awkward positions
  • Restrain firmly and work quickly
  • Consider chemical restraint
  • Exposure time: Motion usually not detected at exposures less than 1/30 second
• Distortion


  • Foreshortening (B) - objects at an angle appear short
  • End on view (C) - long objects appear as spots
  • The body part of interest should be parallel to the film (A)
• The 4 Tissue Densities

  • Gas (Least dense)
  • Fat
  • Water
  • Bone (Most dense)