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What is an x-ray?
Electomagnetic wave that has a shorter wavelength than visible light
Wavelength is indirectly proportional to the energy produced, therefore a longer wavelength has a _____ amount of energy, and a shorter wavelength has a _____ amount of energy.
The greater the energy of the x-ray beam, the _____ its penetration.
The ability of a x-ray to penetrate an object depends on what two factors?
Energy of the x-ray and density of the object
What are the four properties of x-rays discussed in class?
- Ability to penetrate objects that absorb or reflect visible light
- Cause some substances to emit radiation of longer wavelengths or fluoresce
- Produce radiographic images that become visible through processing
- Ability to ionize atoms in substances that they pass through
Name the basic structures of the x-ray tube in the x-ray machine.
- Anode (+)
- Cathode (-)
- Glass envelope
- Lead housing
How are x-rays produced?
Heat from the cathode causes the electrons to detach from the filament. The electrons then travel to the anode through the application of high voltage. When the electrons collide with the anode, the sudden impact creates heat and x-ray production.
What is thermionic emission?
The process of electrons boiling off the cathode filament. A hotter filament boils off more electrons.
kVp controls ____________, while mA controls ____________.
Energy production (speed) of x-rays; # of electrons produced
What type of crystal does radiographic cassette film contain?
What are the compontents of the cathode, and what are the functions of each?
- Filament: provide the electrons with energy through heat production
- Focusing cup: hold filaments and redirects electrons which are off course
- Electrical circuits: produce high voltage (kilovoltage) or low voltage (milliamperage)
The cathode holds a ___ charge and the anode holds a ___ charge.
What are the two types of anodes?
Stationary and rotating
Why is the target area of the anode angled?
To allow the x-rays to leave the tube through the window
Where might a stationary anode be found?
- Older x-ray machines
- Dental equipment
- Small portable x-ray machines
Where might a rotating anode be found?
Higher powered x-ray machines
Rotating anodes produce what quality of radiographs?
99% of kinetic energy from an electron is converted into ___, and the other 1% is converted into ___.
What is the kilovoltage (kVp) responsible for and what does it influence in the radiograph?
The speed of the electrons from the cathode to the anode and determines the penetrating ability of the x-rays. It influences the contrast (shades of gray) of the radiograph.
Low contrast is produced by _____ the kVp, while high contrast is produced by ____ the kVp.
What is milliamperage (mA) responsible for and what does it influence on the radiograph?
The amount of electrons produced by the cathode, which then influences the amount of x-rays produced. It influences the film density.
What is the focal spot? Where is it located?
The size of the electron beam being produced from the cathode to the anode. It's location is on the anode.
A large focal spot results in _____, while a smaller focal spot produces _____ images.
Loss of detail; higher-quality
Describe what the heel effect is.
The angle of the target area determines the intensity of the x-ray beam based on how many of the electrons are absorbed by the anode and target area. The x-ray beam closest to the cathode is more intense due to more electrons being absorbed by the anode and target area on the anode side of the x-ray machine.
How are the mAs calculated?
mA x seconds (s)
What are the 5 types of x-ray machines?
- Mobile units
What are characteristics of the portable x-ray machine?
- Stationary anode
- Single filament
- Single focal spot
- Lower strength (up to 90 kVp, 10 mA)
- Light weight & easy to travel with
- Less sheilding & power
- More motion (poorer quality)
What are characteristics of mobile x-ray units?
- Stationary or rotating anode
- Double filament (higher mAs)
- Variable focal spot size
- Medium strength (max 125 kVp, 300 mA & 1/120 sec)
- Stationary or mobile
What are characteristics of stationary x-ray machines?
- Not mobile & units require installation in radiology rooms w/ proper shielding
- Cannot remove tube from mount
- Higher strength (300mA to 500mA, 125kVp & 1/60 -1/120 sec)
- Foot pedals
What are some characteristics of digital x-ray machines?
- Image displays directly on screen
- No film, screens or processing required
Computed radiography (CR) requires special _____ for digital development.
What are some characteristics of fluoroscopy?
- Tube under table
- Real time images on screens or tape
- C-arm mobile
- Radiation risk greatly increased
What should never be used on a x-ray machine to disinfect the table? Where may this be used in the radiology room?
Bleach may not be used on the table, but it should be used on the floors (unless otherwise stated)
How should the x-ray machine be cleaned?
Wiped down w/ a soft cloth. Any liquid substances may cause problems with electric circuits, therefore they should not be used on the x-ray machine.
What is the only self-serviceable item of the x-ray machine?
As a veterinary technician, you will never service the x-ray ____, ____, and ____ for maintenance purposes.
Machine, processor and chemicals
What effects can radiation have on tissues and liquid?
Ionize the tissue and liquid and cause damage to important structures in the cell. Repeated exposure may cause cells to become carcinogenic, and affected DNA may be passed on.
What type of organ systems are most sensitive to radiation? Give examples.
- Organ systems w/ rapidly dividing cells, such as:
- Reproductive organs
- Bone marrow
- Thyroid gland
- Intestinal epithelium
- Lens of the eye
- Developing fetus (especially during organogenesis)
What are the sources of ionizing radiation?
- CT scans
- Nuclear medicine
Explain roentgen (R).
It is a unit of measure used to determine the amount of radiation an object has been exposed to.
What is RAD and what does it determine?
- Radiation absored dose
- A unit that determines the amount of ionizing radiation that is absorbed by an object
What is REM and what does it determine?
- Roentgen equivalent man
- The amount of radiation that is absorbed by human tissue that has the same effects as 1 roentgen
What is MPD? Who is it set by and what are the maximum doses allowed per week? Per year? In a lifetime?
- Maximum permissible dose: highest amount of radiation a person can be exposed to over a period of time to prevent harm from radiation exposure.
- US Nuclear Regulatory Commission
- 0.1 rem/wk
- 5 rem/yr
- 15 rem/lifetime
What is the purpose of the dosimeter badge?
To record how much radiation a person is exposed to
What factors may affect readings on the dosimeter badge?
- Chemical fumes
What are the four types of dosimeter badges?
- Film badge
- Optically stimulated luminescence badges
- Ion chambers
How does the film dosimeter badge work?
A piece of film is housed in a light proof casing and the exposure amount is measured by how black the film is when it is developed
How does the thermoluminescent dosimeter badge work?
Contain lithium fluoride or calcium fluoride crystals that when processed release light that is proportional to the amount of radiation the badge has been exposed to.
How does the optically stimulated luminescence badge work?
A light laser causes the aluminum oxide between 3 element filters to illuminate in proportion with the amount of radiation exposure
How does the ion chamber dosimeter badge work?
Electrometer charges the chamber and the charge degrades in proportion to the radiation exposure
Goves reduce exposure from the primary beam by what %?
The patient, table and floor are examples of objects that are exposed to what while taking a radiograph?
What are the sources of radiation exposure associated with radiology?
- Primary beam
- Scatter radiation
- X-ray tube head
What are the three methods of decreasing exposure to ionizing radiation?
- Decrease exposure time
- Maximize distance from machine
- Use shielding
Exposure is inversely related to the square of the distance from the source of radiation. What does this mean?
- Doubling distance from the source of radiation decreases exposure by 4 fold (22 = 4 = only exposed to 1/4 the radiation)
While taking a radiograph, what should you do to minimize exposure?
- Lean back and look away
- Stay as far away as possible
- Do not place portible units in lap or hold them with hands
How can time be reduced when taking a radiograph?
- Use fast film screens
- Avoid retakes (appropriate use of technique charts & darkroom practices)
What does the collimator do?
Show size of primary beam & adjusts size of primary beam
Scatter radiation decreases ____ quality and increases the danger to the operator.
mAs are directly related to the patient dose, meaning?
When mAs go up, patient dose also goes up & when mAs go down, patient dose goes down
Why does an increase in mAs increase the patient dose?
mAs are directly related to the number of electrons being produced, and therefore it increases the amount of x-rays being produced
What is proper radiographic PPE?
Lead gowns, gloves (both top & bottom protection), thyroid shield, and glasses (if available)
How should lead apparel be handled/stored?
- Apron hung or draped to prevent cracks through folds and wrinkles
- Gloves hung open to allow air circulation or placed w/ cans inside
What are the exposure factors that may affect technique?
- Time of exposure
- Millamperage (mA)
- Kilovoltage (kVp)
- Focal film distance
- Type of intensifying screen
- Type of film
- Table top vs grid technique
mA has an inverse relationship with what factor? And a direct relationship with what?
Time; # of x-rays produced
A longer exposure time allows for what?
More time for the electrons to travel from the cathode to the anode, which causes an increase in x-ray production due to the 1:1 relationship between electrons and x-rays
mAs is a product of what? What is the most desirable setting of mA and s?
- mA and exposure time
- The highest mA and shortest exposure time possible is most desirable
Increasing the kVp will cause what? Explain. What happens if the kVp is too high?
- An increase in kVp will cause an increased penetration of tissues because kVp controls the attraction of the electrons to the anode. A higher kVp causes an increased force in electrons.
- To high of a kVp will cause more poor contrast
What is the focal film distance and how does it affect the quality of the radiographic image? What is the best range for focal film distance?
- The distance between the target on the anode and the film cassette. The relationship between the focal film distance and x-ray intensity is inversely proportional, so the further the distance, the better the image (so long as the x-rays can penetrate the tissues).
- Best range is b/w 36 - 40 inches
What is radiographic contrast? Describe the distance b/w high contrast (short latitude) and low contrast (long latitude).
- The difference between densities of tissues.
- High contrast (short latitude) gives fewer shades of gray due to extreme differences in density
- Low contrast (long latitude) gives more shades of gray (less difference b/w shades) due to more similar densities of tissues
What factors affect radiographic contrast?
- Subject density
- kVp level
- Film contrast
- Film fogging
List tissues in order from highest density to the lowest density.
Metal -> bone -> water/muscle -> fat -> air
What may cause film fogging? What effect does fogging have on the film?
- Heat, low grade light exposure, scatter radiation
- Decreases contrast
Why does a low kVp produce a higher contrast? Why does high kVp produce low contrast?
- More x-rays are absorbed into tissues with low kVp
- More x-rays penetrate the tissues with a high kVp, which allows for more shades of gray
What is the 16% rule? What setting does it apply to?
Increasing the kVp 16% will double kVp, where decreasing the kVp 16% will half kVp
An x-ray is taken @ 70 kVp. The image comes out with too low a contrast and we want to decrease kVp by 8%. What is the new kVp?
- 8/100 = x/70
- = 560/100
- = 5.6
- = 6
- 70 - 6 = 64 kVp
When would a nonscreen cassette be used? What increases with this type of screen and what type of studies are they typically used for?
- When great detail is needed
- It requires a longer exposure time
- Used for intraoral studies, nasal passages, and dental arcades
What is the nonscreen film encased in?
Cardboard or plastic holders
What is the purpose of the image intensifying screen? What contents allow for this to happen?
- Amplify the radiographic effect of the x-rays
- The flourescent crystals in the screen allow for this process
How many photons does one x-ray photon produce when absorbed by the intensifying screen?
1000 light photons
What is the flourescence exposure to direct x-ray exposure percent ratio of radiographic density?
What are the layers of the intensifying screen and what does each layer contain?
- Base: plastic/cardboard backing
- Reflective layer: titanium dioxide
- Phosphor layer: light emitting crystals
- Protective waterproof coat
What are the two light emitting crystals discussed in class and what color light goes with each?
- Calcium tungstate: blue light
- Rare Earth Phosphors: green light
What is a special characteristic of the rare earth phosphor crystals?
Higher ability to convert x-rays into light which decreases time
What does the protective waterproof coat of the intensifying screen prevent &/or allow?
- Static protection
- Physical protection
- Washable surface
What can you clean the intensifying screen with?
- Screen cleaner
- Distilled water
- 70% isopropyl alcohol
Describe the qualities of each screen speed: slow, par, high
- Slow: high definition, better detail
- Par: good resolution, minimum exposure
- High: fast speed, more exposure required for thick tissue, reduce patient exposure, appears grainy
Screen speed is inversely proportional to what? What does this mean?
- Exposure time
- High speed screen require less time, where slow speed screens require more time
What factors determine the screen speed? How does each factor effect the screen speed?
- Thickness of the phosphor layer: thicker layer emits more light which makes speed faster, but light is difuse and causes a more blurred image
- Phosphor crystal size: larger crystals emit more light, thus increases the speed, but image is grainier
- Light absorbing dyes: increase detail by trapping lateral spreading scatter radiation
Is film a legal document?
Yes, it is a permanent record of a dx
What is film composed of?
- Polyester base
- Light sensitive emulsion coating both sides
- Outer coat of clear protective gelatin
The emulsion coating of film is composed of what? How many are present per cubic centimeter?
- Silver halide crystals
- Billions per cubic cm
Describe the developing process
- 1. Light from x-rays and the screen are absorbed by the film. Silver halide crystals become sensitive to chemical change, forming the latent image
- 2. Developer converts silver halide crystals to black metallic silver
- 3. Fixer removes unexposed silver halide crystals from the film
What will happen to a film that is not exposed that is developed?
Will come out clear due to no conversion of silver
What are the two film types discussed in class?
Screen film and direct exposure (nonscreen)
Screen film is more sensitive to light from what source?
What is the blue sensitive film? Green?
- Calcium tungstate and some rare earth phosphor screen -blue
- Rare earth phosphor screen - green
What influences the speed of the film?
Size of silver halide crystals
List characteristics of slow speed film (100)
- Small crystals
- Longer exposure time
- Greater detail
List characteristics of par speed film (200)
Compromise b/w time and exposure
List characteristics of fast speed film (400 - 800)
- Large crystals
- Grainy detail
- Short epxposure time
What is radiographic quality?
How clear the details on a radiograph are
What factors influence the quality of the radiograph?
- Radiographic density
- Quantum mottle
- Proper labeling
How can equipment affect radiographic quality?
- Maximum settings and condition of the x-ray machine
- Clean rollers, freshness of solutions, maintenance of processor
How does mA effect the radiographic quality?
Too high of an mAs can cause darkness of the film, but too low may cause poor radiographic density
How does kVp effect the radiographic quality?
Too high of a kVp will cause electrons to penetrate tissues and effect the contrast of the image, while too low of a kVp may cause high contrast