Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
67 Cards in this Set
- Front
- Back
|
How are Xrays produced?
|
Xrays are produced by bombarding a target with an electron beam. The Electrons begin in the Cathode and are accelerated to the Positive Anode.
|
|
|
X-ray beams can be described as Polychromatic; meaning the X-ray tube produces a combination of both general and characteristic x-rays. What is the difference between general and characteristic x-rays?
|
The general x-rays are a variety of energy levels; where as characteristic x-rays are at a specific energy level.
|
|
|
The faster electrons are accelerated toward the positive Anode and target the ______ energy they will carry.
|
The faster the electrons are accelerated toward the Positive Anode and target the more energy they will carry.
|
|
|
The target is within which portion of the the Xray tube, Cathode or Anode?
|
The Target is within the Anode and recieves the electrons from the Cathode, negative side.
|
|
|
Polychromatic X-ray beam is a beam of _____ energies.
|
Polychromatic is a x-rays beam of multiple energies.
|
|
|
Describe Coulombs Law.
|
Like Charges repel; unlike charges attract.
The closer the charges the stronger that force of attraction if unlike charges or rejection if like charges. |
|
|
The wavelength is ____ proportional to the energy.
|
The wavelength is inversely proportional to the energy. X-rays have decreased wavelength but increased frequency and energy.
|
|
|
As wavelength decreases, the energy increases; therefore a short wavelength as in the case of X-rays would give _____ energy.
|
A short wavelength gives a high energy.
|
|
|
Electromagnetic radiation travels in what direction?
|
Electromagnetic radiation travels in a straight line. All forms of electromagnetic radiation travel at the speed of 186,282 miles/second.
|
|
|
T/F: X-rays can penetrate matter and will cause biological damage to the tissues.
|
True. Light can not penetrate matter, hance a shadow when you are standing in the sun. X-rays can penetrate matter and can hit the DNA in your body causing damage.
|
|
|
Who discovered X-rays?
|
X-rays were discovered by Wilhelm Roentgen in 1895
|
|
|
Name the Components of an xrays machine. There are 6!
|
Anode
Cathode Rotor Tube Housing Focal Spot Target |
|
|
X-ray tubes have 2 seperate electrical circuits that operate different functions; the low voltage circuit operates which aspect?
|
The Low voltage circuit operates the Cathode.
The High voltage circuit operates the Anode AND the cathode. |
|
|
The Cathode is the negative portion of the X-rays tube and contains a coiled wire called a ____?
|
The cathode contains a coiled wire called a filament. This filament is heated by the low voltage circuit
|
|
|
T/F: The Filament is the source of electrons.
|
The filament resides in the cathode, is heated by the low voltage circuit and as it gets hotter becomes a source of electrons. An electron cloud develops as the electrons boil off the filament in a process called Thermionic Emission.
|
|
|
An electron cloud develops around the filament within the cathode in a process called?
|
Thermionic Emission
|
|
|
Within the Cathode is a Focusing Cup, what is it's function?
|
The focusing cup is in a metal shroud that focuses the electrons to a specific point on the anode. The focusing cup keeps the electrons gathered around the filament as the cloud forms.
|
|
|
When machines have more than one filament in the Cathode the small filament is used for low output exposures when what kind of detail is needed?
|
The small filament is used for low output exposures where high detail is needed.
The large filament is used for high output exposures, lots of x-rays produced but lose detail/resolution. |
|
|
Small filament = small amount of x-rays, but high detail.
Large filament = ? |
Large filament = Large number of x-rays but poor resolution
|
|
|
The Cathode was on a low voltage circuit where as the Anode has both a low and high voltage circuit. The high voltage is applied at what time?
|
The high voltage circuit is applied during the time of the exposure to create a voltage differential from the cathode (-) to the anode (+). This higher voltage serves as a greater degree of attraction for the electrons to move toward.
|
|
|
The negatively charged electrons are accelerated toward the positively charged ____?
|
The negatively charged electrons are accelerated towards the positively charged Anode. This is Columbs Laws, opposite charges attract.
|
|
|
When the electrons hit the target of the Anode describe what happens?
|
The negatively charged electrons are accelerated towards the positively charge Anode where they strike a target made of Tungsten. The electrons interact with the Tungsten atoms to produce Xrays. The Electrons may pass by the atoms and give off general radiation of many energies or may directly impact an atom and give off characteristic energy of one level.
|
|
|
An x-ray tube converts the kinetic energy of accelerated electrons into x-rays. What happens to the majority of this kinetic energy?
|
The majority (99%) of the kinetic energy of the electrons is converted to heat; only 1 percent is actually converted to x-rays. For this reason most advancements in x-ray tube desgin are focused on heat dissipation.
|
|
|
Why is heat created from the electrons and kinetic energy a problem?
|
The majority of kinetic energy of the electrons is converted to heat and can melt the Anode (+) if not adequately dissipated.
|
|
|
The anode is made of what substance?
|
The Anode (+) is made of Copper with a tungsten insert that is the target; surface the electrons contact.
|
|
|
What is the Focal Spot?
|
The focal spot is the area of the target where the electron beam is focused and the location where the xrays are produced. The metal may actually be pitted by the energy of the electron beam as it contacts the tungsten.
|
|
|
What is the Heel effect?
|
The Heel effect is caused by the angle of the Anode. The Anode is on an angle so xrays exit the target and head down to the patient at uneven intensities. Those x-rays on the Anode side of the beam must travel a greater distance through the target before exiting the target. This extended length of travel leads to a greater absorption of energy by the target and less intensity for those xrays on the anode side of the beam.
|
|
|
Because of the Heel effect what would be the best route of positioning for your radiograph of a lateral thorax?
|
The Heel effect causes x-rays of the Cathode (-) side of the beam to be at a higher intensity b/c they spend less time in the target, so position the thickest portion of your patient in the direction of those x-rays on the cathode side to ensure proper penetration.
|
|
|
Energy of the beam = ?
|
Energy of the beam = Quality
Number of X-rays in the beam = Quantity |
|
|
mA Selector controls the low voltage circuit, meaning which portions?
|
mA Selector is the low voltage circuit. mA controls the current to the filament within the Cathode (-), the source of electrons.
The more current applied to this circuit the hotter the filament, the more electrons are boiled off, and the more x-rays can be produced. |
|
|
If you double the mAs you?
|
Double the mAs, will double the number of electrons produced, and therefore the number of x-rays produced.
|
|
|
mA selector controls X-ray ____?
|
Quantity. The mA is the low voltage circuit that controls the current within the filament, it control how many electrons are produced; it does nothing to their energy.
|
|
|
kVp is a high voltage circuit, so this would have to be control of the Anode side. KVp therefore control what?
|
The high voltage circuit applies a voltage differential from the cathode to the anode during exposure. The kVp selector controls this voltage differential. The greater the voltage difference the faster the electrons are accelerated, the higher the kinetic energy, and the higher energy of the x-rays.
|
|
|
Increase the kVp and you will ___?
|
Increase the kVp and you increase the voltage difference between the anode (+) and the cathode (-) and the energy of the x-rays. In addition kVp will increase the number of x-rays, just as mA did.
|
|
|
Higher energy beams allow better penetration as in the case of ?
|
Higher energy beams are required for thicker body parts, and therefore require high kVp for better penetration of the tissue.
|
|
|
mA = Quantity
kVp = ? |
Quality AND quantity
|
|
|
Energy of the beam determines the beam ?
|
Penetration. Controlled by kVp, if you burned through it, too high energy.
|
|
|
The x-ray beam energy ranges from zero to the value of the kVp, it can not be higher than the set kVp but is often lower. How much lower?
|
The average energy of the beam will be only 1/2 to 1/3 of the kVp.
|
|
|
Increase the kVp and you increase?
|
Increase kVp and it increases the number of x-rays, energy, quality, quantity, and penetration of the beam.
|
|
|
The Timer controls the duration of the exposure, the time the voltage potential is placed across the anode and cathode. So if you increase the timer you ?
|
Electrons will continue to flow and xrays will be produced as long as the voltage potential is applied so increasing the timer simply increases the number of x-rays produced.
|
|
|
T/F:
mAs = mA x Time (in seconds) Therefore doubling the mA will have the exact effect as doubling the time, the end result is a doubled mAs. |
True, still not changing the energy of the x-rays or beam.
|
|
|
What is the biggest factor in x-ray machine cost?
|
mA is the biggest factor in xray machine cost, its the horsepower. The higher the mA of the machine the more x-rays it can produce and therefore the more powerful the machine is.
|
|
|
The x-rays tube is encased in a metal housing that contains lead to shield x-rays produced in which directions?
|
The x-rays tube is encased in a metal housing that contains lead to shield x-rays produced in directions other than the patient.
|
|
|
What do collimators do?
|
Collimators restrict the x-ray beam to a confined region. They are located outside the tube housing and may be fixed as a cone, cylinder, or diaphragm. The better collimators have adjustable shutters.
|
|
|
Collimation of the x-ray beam will reduce patient exposure by limiting the area of iiradiation, what else do they do?
|
Collimators reduce patient exposure but also improve image quality through better contrast by reducing the scatter radiation.
|
|
|
Scatter radiation do not help with radiographs; they instead?
|
Scatter radiation decreases image contrast.
|
|
|
Grids are devices used to prevent scatter radiation from reaching the film, this is important b/c Scatter radiation do not help with radiographs; they instead?
|
Scatter radiation decreases film quality by reducing image contrast.
The grid sits between the patient and the image receptor/cassette. |
|
|
What are grids composed of?
|
Grid are composed of hundreds of alternating lead strips. Primary radiation, from the beam, will travel in a straight line from the target down to the patient and pass through the spaces within the grid.
|
|
|
Scatter does not travel in a straight line and is therefore stopped by ____?
|
Scatter radiation travels in different directions as it bounces off objects, it is stopped by the lead strips of the grid and are therefore prevented from hitting the cassette/image receptor.
|
|
|
The thicker the body part the more scatter radiation is produced and the greater penetration will be needed so higher kVp. What is the recommendation for grid use?
|
Any tissue greater than 10 cm should be imaged using a grid.
|
|
|
Grids vary in their ability to remove scatter radiation and are designed by a term called the gird ratio. What is Grid ratio?
|
Grid Ratio is the height of the grid strip divided by the width of the interspace material. A high grid ratio is more effective in removing scatter than a low grid ratio. Taller and skinner = High grid ratio.
|
|
|
When using a grid what control must be altered and in what way?
|
If scatter is removed by the grid then more radiation is needed to adequately expose the film. Since more radiation is needed (quantity not quality), radiographic technique is modified when using a grid by increasing the mAs.
|
|
|
Grid ratio tells you how much to increase the mAs. If you have a high grid ratio, its tall and skinny, good for collecting scatter and therefore how would you alter mAs?
|
Grid Ratio 12:1 = mAs 4x higher
Grid Ratio 5:1 = mAs 2x higher |
|
|
What are cassettes?
|
Cassettes are rigid, light-tight devices that hold x-ray film in contact with the intensifying screens. There is an intensifying screen above and below the film, within the cassette.
|
|
|
What is the function of the screen?
|
The function of the screen is to convert the energy of the x-rays into visible light. It is this light that exposes the x-ray film.
|
|
|
The efficacy of exposing x-ray film with light from intensifying screens is much higher than with x-rays alone. Infact about what percent of the film is exposed by just x-rays?
|
Only about 1% of the film exposure is directly from x-rays. Radiation from the beam, causes the screen to give off a white or colored light that goes to the film and exposes it.
|
|
|
Where are the screens located?
|
Screen line the inner surfaces of the cassette, the film is placed between the screens when the cassette is closed.
|
|
|
When radiation travels down the beam, through the patient, and to the cassette, the x-ray photon will strike the phosphor crystal in the screen exciting the phosphor crystal so that it emits a specific wavelength of light that exposed the film. What is the efficiency of the screen based on?
The efficiency of the screen is |
The efficiency of the screen is based on:
Thickness of phosphor layer The type of phosphor crystal The size of the phosphor crystal |
|
|
Thicker screens cause spreading of light and the end result is ?
|
Thicker screens causes poor resolution/image detail, the film becomes black. The best resolution is actually that without a screen but would require a lot more radiation to do so.
|
|
|
An important function of the cassette is to hold the screen and film in contact, what is the result of a failure in this?
|
If there is a loss of contact between the screens and film a light spread will occur and a decrease in detail. Lose resolution is the screen is not touching.
|
|
|
Screen speed is a relative number used to identify the efficiency of conversion of x-rays into usable light, speed is inversely related to detail. So a high speed screen, is highly sensitive requiring less radiation, but will have poor resolution/image detail. Low number screens are therefore best for ?
|
Low number screens are considered detail screens but do require more radiation exposure.
|
|
|
Screens can be identified according to three broad categories
High Speed 400 to 1200 Par Speed 100 Fine Detail 50-100 Which screens would you buy if your machine was a high mA machine? |
mA is the quantity of electrons and therefore x-rays produced, so if your machine has the ability to produce lots of x-rays you can afford to use lower number/speed screens and just turn up the mA to get enough radiation to expose the film.
If you have a machine that is only capable of low mA settings you will need a long exposure time to expose film, which could allow for motion artifacts, so chose a high speed screen as it requires less radiation; knowing you will lose image detail. Higher mA, can buy cassette with lower speed- better resolution |
|
|
Your technique using a 200 speed screen is 10 mAs
What is your technique if you change to a 400 speed screen? |
= 10mAs x 200 (old speed)/400 (new speed)
= 5mAs |
|
|
If your equipment is high output, large mA ability, what screen speed would you choose?
|
If your equipment is high output then you may select a slower speed screen when you need good detail (orthopedic, spinal and exotic animal radiographs)
Slow screens require high radiation which you have the ability to provide and in exchange you get great detail. |
|
|
T/F: It is important that the wavelength of light emitted by the screen matches the sensitivity of the film.
|
True
|
|
|
Radiographic film is composed of a clear or blue tinted base material (polyester) with an emulsion on one or both sides. The emulsion is the most important component of the film. What is in the emulsion?
|
The emulsion is a homogeneous mixture containing silver halide crystals. The silver halide crystals are flat and triangular in shape, approximately 1 ųm in diameter. They are 95% Bromide and 5% Iodide.
|
|
|
What is the Sensitivity Speck?
|
The emulsion is made up of silver halide crystals, 95% Bromide and 5% Iodide both negatively charged, but there is a contaminant of Silver Sulfide that is positively charged and called the Sensitivity Speck.
Free electrons from the light photons combine with this positive speck, become entrapped, creating Metallic silver deposits that form the latent image. |
