Rad1 Flashcards
X-rays are…
a form of electromagnetic radiation
X-rays are similar to visible light but…
- Can not be seen, felt, heard
* Carry more energy-more likely to cause injury
Possible outcomes when living tissue is exposed to X-rays
- X-rays pass through tissue w/ no effect
- Produce cell damage that is repairable
- Produce cell damage that is nor repairable
- Kill cell
X-rays damage living tissue by …
imparting ionizing radiation that can alter the normal chemical structure of biological molecules
Types of radiation injuries
- Skin burns, cataracts, anemia cancer (somatic damage)
- Birth defects–>skeletal/dental malformation, mental retardation, microphthalmia (genetic damage)
- Rapidly reproducing cells most commonly affected
Sources of radiation
- X-ray machines
- Radioactive materials from nuclear plants
- Background–> Cosmic rays, building materials, earth’s crust, the body
RAD
(radiation absorbed dose)–
measure how much ionizing radiation is absorbed by an individual
REMs
(Roentgen equivalent man)
measure of the amount of ionizing radiation and it’s ability to cause tissue damage
– also known as radiation dose equivalent
Sievert (Sv
another unit used to express radiation dose equivalent measurements
1 Sv = 100 rem
gray units (Gy)
Radiation exposure can also be measured using gray units (Gy)
1 GY = 100 rad
Dosimeters
devices used to measure radiation exposure
o Film badge
o Thermo-Luminescent Dosimeter (TLD)
• Dosimeters must be worn when taking radiographic exposures
Basis of X-ray Radiation
- X-rays are a form of energy
- Part of the electromagnetic spectrum
- X-rays can be produced in a laboratory by directing high speed electrons at a target atom
Maximum Permissible Dose (MPD)
amount of radiation an individual may receive w/o suffering appreciable bodily injury during a lifetime
Minimum safety standards
• set by federal government
• Maximum Permissible Dose
o 5 rem/yr (0.05 Sv/yr)
• No one under 18 is allowed to work w/ ionizing radiation equipment
• Pregnant women have lower limitsPhysical properties of X-rays
- Penetrate materials that absorb or reflect visible light
- Travel in a straight line
- Cause certain substances to fluoresce
- Cause chemical changes on radiographic film that form a visible image after development
- Cause injury to living tissue
Four components necessary for X-ray production
- Source of electrons
- Method of accelerating electrons
- Obstacle-free path for the passage of fast speed electrons
- A target w/ which electrons can interact to produce X-rays
Cathode
Made of molybdenum cup and tungsten filament
Anode
Beveled tungsten target on a copper base
Glass envelope
Creates vacuum between cathode and anode
Acceleration of electrons
Electrical potential difference created between cathode and anode
radiograph film
- Polyester base w/ a gelatin emulsion cover
- Exposure to visible light or X-rays causes chemical changes in silver halide crystals
- Screen film is more sensitive to fluorescent light than X-rays
- Nonscreen film is more sensitive to X-rays
- Speed correlates with the amount of radiation necessary to make a radiograph
Intensifying screens
- Used w/ screen film
- Reduce the amount of radiation necessary to make a radiograph
- Plastic base w/ a phosphor crystal layer cover
- Emit a fluorescent light that causes 95% of screen film exposure
- Screen speed correlates with the amount of radiation necessary to make a radiograph
Cassette
• Light-tight container that holds the film and intensifying screens in close contact
• Materials
o Front- polycarbonate, aluminum, magnesium, carbon fiber
o Back- a heavy material lined with lead
Digital image receptors
- Convert an analog signal (i.e. visible light produced by special intensifying screens) into a digital, electrical signal
- The digital electrical signals are used to create pixels (picture elements) that form a visible radiographic image on a computer monitor
CR systems
Digital image receptors may resemble and be used in the same manner as a conventional X-ray film cassette
Advantages of digital image receptors over conventional X-ray film
o Eliminates the need of X-ray film processing
o Better images that are made faster with fewer mistakes (i.e. retakes)
o Images can be manipulated (size, degree of darkness, contrast, measurements can be made, images can be sent)
CR vs. DR systems
o DR systems have a higher startup cost
o DR systems require no cassette handling faster image acquisition
o CR systems can be used for horizontal and vertical film images
Controllable components of the X-ray machine that play a role in the formation of the radiographic image
o Milliamperage
o Exposure Time
o Kilovoltage Peak
o Focal-Film Distance
Milliamperage (mA)
o Measure of the electrical current that is used to heat the wire filament at the cathode
o The temperature reached by filament is directly related to the # of electrons that are freed from their orbits to travel to the anode
Exposure Time
o Controls the period of time during which X-rays are actually produced in the X-ray tube
exposure time ~ # of X-rays produced
Both mA and exposure time control…
mA x exposure time =
• the # of X-rays produced during a radiographic exposure
= # of X-rays produced
Kilovoltage Peak (kVp)
• Measure of the electrical potential difference between the cathode (-) and the anode (+)
Focal-Film Distance (FFD)
o The distance between the focal spot in the X-ray tube and the X-ray film
o FFD affects the # of X-rays that reach the film during a radiographic exposure
Inverse square law
The intensity of the beam is reduced by 1/4th when you double the distance from the source
Visual quality of a radiograph image is assessed by looking at
o Radiographic density-
o Radiographic contrast
o Radiographic detail-
o Radiographic distortion
Radiographic density
o Dependent on the # of X-rays reaching the film
o The more X-rays to reach the film, the greater the blackness and the greater the density
Exposure Factors affecting radiographic density
o mA-s determines the number of X-rays produced, inc. mA-s inc. radiographic density
o kVp determines penetrating power of X-rays, inc. kVp inc. radiographic density
o FFD the farther the film is from the X-ray tube, the fewer the X-rays that reach the film and the lower the radiographic density
Film processing and patient factors affecting radiographic density
Developing time
Developing temperature
Tissue thickness and tissue density of subject being radiographed
Radiographic contrast
visible difference between two adjacent structures on a film
o Dependent on variations in penetrating power of X-rays
High contrast
black and white tones w/ very few gray tones
Low contrast
many gray tones between black and white tones
Exposure factors affecting radiographic contrast
kVp Variations in kVp and the penetrating power of X-rays can create more or fewer shades of gray on a radiograph
Patient and other factors affecting radiographic contrast
Differences in tissue thickness/density of the part being radiographed affect radiographic contrast
Scatter radiation non-image forming X-rays that expose inappropriate area of the film and decrease radiographic contrast
Radiographic detail
image sharpness, clarity
Factors affecting radiographic detail
Focal spot size
FFD
Animal motion
Screen-Film contact
Radiographic distortion
change from the original size and shape of the subject being radiographed
Distortion is Prevent by
Positioning subject as close to cassette as possible
Positioning point of interest in the center of the X-ray beam
Positioning subject parallel to cassette
Technique Chart
- A document that lists predetermined exposure factor settings based on the thickness of the region of the animal’s body being radiographed
- Provides a consistent method for choosing the correct exposure factor settings
- Avoids having to recalculate exposure factor settings each time a radiograph is taken
Variables affecting technique chart formulation include:
o X-ray machine (calibration, line voltage)
o Animal species: Bird vs. Horse
o Anatomical Region
Extremities Thorax, Abdomen
Determine kVp requirement using Santes’ rule:
2 X tissue thickness in cm + FFD in inches + grid factor = kVp
o Grid factor must be added to compensate for primary X-rays absorbed by the grid during exposure
Determine mA and exposure time settings
o mA typically set to highest setting to avoid motion artifact on radiograph
o Exposure time set based on mA-s requirement for region of body and the speed of intensifying screen/film being used
Patient Restraint for Large animal
• Be careful when handling animal
o Introduce animal to X-ray machine, cassette
o Avoid sudden movement, loud noises
• Sedation, twitches, stocks can be used if necessary
Equipment for Large animal
- X-ray machine used must be maneuverable
- Portable units
- Mobile modular units
- Mounted units
Patient Preparation for Large animal
• Part of animal being radiographed must be clean and dry • For hoof radiographs: o Remove horseshoe o Pack sole with Play Doh • Positioning Devices o Wooden blocks, cassette tunnel
Radiation Safety for Large animal
- Safety rules discussed for small animals still apply
- Use cassette-holding devices
- Make sure assistants are not in the path of the primary beam
