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X-ray phisics 3

QuestionAnswer
What are the five basic interactions between x-ray and matter? Photoelectric absorption, Compton scattering, coherent scattering, Pair production, photodisintegration.
Which 2 interactions have a significant impact on x-ray image? Photoelectric absorption and Compton Scattering.
How does photoelectric absorption occurs? Incident electron interacts with an inner-shell electron (K-shell), ionizing the atom. The K-shell vacancy is then filled by an electron of L-shell or less common M-shell, producing a characteristic photon known as secondary radiation.
The percentage of photoelectric interactions_______ with an _____ Kvp decreases, increased.
photoelectric absorption interactions ___ as atomic number ___ Increases, Increases.
Photoelectric interactions occur more in? Bone
For a photoelectric absorption to occur what should happen? Incident photon energy must be higher than the binding energy of the inner-shell electron.
How does Compton scattering occurs? Incident photon interacts with an outer-shell electron, removes the electron from its shell, proceeding in different directions as scatter radiation.
The ____ the initial energy of the photon, the ____ the energy of scatter photon. Higher, higher.
zero angle deflection no energy is transferred
The percentage of Compton interactions ____ with ___ kvP increases, increased.
As the angle of deflection increases to ___, more energy is transmitted to the____ and less energy remains with the____. 180 degrees, recoil electron , scattered photon.
When a scattered photon is deflected back toward the source and travels in opposite direction to the incident photon. these photons are called? Backscatter radiation.
when photoelectric effect is more prevalent,what type of contract ww will have in the image? High contrast. (more differences between black and white, less grays)
Photoelectron travels with kinetic energy which is equal to what? the difference between incident photon and binding energy of the inner-shell electron.
Photoelectic equation Ei= Eb+Ekc
Energy transferred in a Compton effect is Ei= Es+Eb+Ekc
Coherent scattering interaction between very low energy x-ray photons and matter, also called classical or unmodified scatter.
occurs with photons less than 10 KeV, is outside the range of diagnostic imaging. Coherent scatter
Pair Production Occurs with high energy x-ray photons, with an energy of at least 1.02 Mev. Therapeutic x-rays.
It loses all of its energy when high energy incident photon comes close to the strong nuclear field. Pair production
Photodisintergration Interaction between extremely high-energy photons. Above 10 MeV and the nucleus.
Why are Iodine and barium useful contrast agents in diagnostic imaging? because they absorb a greater percentage of the photons through photoelectric interaction.
In the human body, which interaction is more predominant? Compton scattering
When photoelectric interactions is more predominant? In lower energy ranges 25-45 KeV (40-70 KvP) and when high atomic number elements are introduced. (Iodine and Barium)
High contrast, low KvP, High mAs = Higher patient doses.
When compton interactions prevail, the result inthe image will have? Low-contrast. (more gray shades in between)
Low contrast, High kvP/ low mAs = reduces patient doses.
Magnetic force field is created when a charge particle is in motion
Electromagnetic induction Moving the conductor, moving magnetic lines of force, change in magnetic flux.
Generator Converts mechanical energy into electrical energy
AC generators uses ____ rings. DC generators uses ____ rings. Slip Commutator
Conventional electric current goes from ____ to ____. Positive to negative poles.
Electron flow from negative to positive.
Alternating Current AC electrons first move in one direction and then reverse and move in the opposite direction.
Direct current DC all electrons travel in the same direction.
In the x-ray circuit, where is the rectification? High voltage side.
Where is the stator located? Outside the envelope. (Anode side)
mA selector is located where in the x-ray circuit? Filament circuit variable resistance
High contrast, low KvP, High mAs = Higher patient doses.
When compton interactions prevail, the result inthe image will have? Low-contrast. (more gray shades in between)
Low contrast, High kvP/ low mAs = reduces patient doses.
How is a magnetic field created? when a charge particle is in motion and is created by electrons spinning.
Conductor in presence of magnetic field. Moving the conductor, moving magnetic lines of force, change in magnetic flux.
Generator Converts mechanical energy into electrical energy
AC generators uses ____ rings. DC generators uses ____ rings. Slip Commutator
Conventional electric current goes from ____ to ____. Positive to negative poles.
Electron flow from negative to positive.
Alternating Current AC electrons first move in one direction and then reverse and move in the opposite direction.
Direct current DC all electrons travel in the same direction.
In the x-ray circuit, where is the rectification? High voltage side.
Where is the stator located? Outside the vacuum of the envelope. (Anode side)
mA selector is located where in the x-ray circuit? Filament circuit variable resistance
High contrast, low KvP, High mAs = Higher patient doses.
When compton interactions prevail, the result inthe image will have? Low-contrast. (more gray shades in between)
Low contrast, High kvP/ low mAs = reduces patient doses.
How is a magnetic field created? when a charge particle is in motion and is created by electrons spinning.
Conductor in presence of magnetic field. Moving the conductor, moving magnetic lines of force, change in magnetic flux.
Generator Converts mechanical energy into electrical energy
AC generators uses ____ rings. DC generators uses ____ rings. Slip Commutator
Conventional electric current goes from ____ to ____. Positive to negative poles.
Electron flow from negative to positive.
Alternating Current AC electrons first move in one direction and then reverse and move in the opposite direction.
Direct current DC all electrons travel in the same direction.
In the x-ray circuit, where is the rectification? High voltage side.
Where is the stator located? Outside the envelope. (Anode side)
mA selector is located where in the x-ray circuit? Filament circuit variable resistance.
Backup Time All AEC equpped units permit a manual backup time to be set to avoid errors.
What four conditions must exist for x-ray production to occur? source of electrons, appropriate target material, high voltage, vacuum.
Parts of the cathode assembly Focusing cup, filament(s), wiring.
Why is tungsten the best material for x-ray source? High melting point, difficult to vaporize, high atomic number enhances diagnostic x-ray photons, heat conducting ability.
Anode Positive side of x-ray tube. serves as target surface for high voltage electrons .
Cathode Negative side of x-ray tube. produces a thermionic cloud
X-ray tube components {Anode(positive) cathode(negative)}{envelope} {encased in protective housing}
Filtration is the elimination of low energy x-ray photons by the insertion of absorbing materials into the primary beam.
Inherent Filtration occurs inside the tube and housing.
Added filtration Occurs outside the tube and housing
How is filtration expressed? in terms of Half-Value layer.
HVL is the amount of absorbing material that will ___ the intensity of the primary beam by ___ its original value decrease, one-half.
Purpose of filtration To reduce patient exposure by eliminating low energy photons that would not enhance the image.
What is attenuation? Is the reduction in the number of x-ray in the beam, and subsequent loss of energy as the beam passes through matter.
The ___ the atomic number of an element the ___ attenuation. Higher, more
The ___ the atomic number of an element the ___ the attenuation. Lower, less
What are the four major substances that account for the variation in x-rays absorption? Air, fat, muscle and bone.
organize previous substances from higher atomic number to lower atomic number. Bone(12.31), Air(7.78), Muscle(7.64)Fat(6.46).
Thicker and denser parts, absorb ___ radiation producing ___ image receptor exposure. more, less.
The ___- the body part, the ___ absorption, ___ Image receptor exposure. thicker, more, less.
What is the purpose of using a grid? Improves contrast in radiographic image.
When should a grid be used? When body part exceed 10 cm. 60 kvp or higher.
the ___ the grid ratio the____ scatter radiation. Higher, less.
Are higher grid ratios more or less prone to errors? More prone.
What is grid frequency? Is the number of grid lines per inch, the most common grid frequency is 85-103 lines/inch.
Grid ratio= h= lead strip height --------------------- D= intespace width
Grid errors Off-level, Off-center, upside-down.
Off-level Results from improper tube and grid positioning.
Upside-down Severe peripheral cut off will occur.
At techniques above 90KVp, it is best to use grids with ___ ratio or higher. 8:1
which is the linear grid with the widest latitude for centering and focus? 6:1
High ratio grid is designed to be used with high Kvp techniques
An exposure with an off-level grid will show grid cutoff where? Across the image
Grids generally have a frequency of ___ lines per inch. 60-110
Contrast on a radiographic image is highest when the amount of ___ id the lowest. Compton scatter
The amount of scatter absorption in a grid depends on? angle of scatter photon, height of the grid strips, width of interspace material.
Film construction Base (polyester) adhesive Emulsion with crystals supercoat
Types of crystals T-grain (flat and triangular) and conventional
What is the purpose of the gelatin in the emulsion? is to act as neutral lucent suspension medium for the silver halide crystals.
During the crystal production what is the waste product that is washed away? Potassium nitrate.
Silver halide crystals must have an impurity to form sensitivity specks. what is this impurity? Gold silver sulfide.
Latent Image refers to the image that exists on film after the film has been exposed but before it has been processed.
Latent image formation -Bromide ion absorbs an incident photon and ejects and electron.-ejected electron is trapped in sensitivity speck, giving it a negative charge.- negative charge sensitivity speck attracts free silver ion.Silver ion neutralizes sensitivity speck.
Panchromatic films sensitive to all colors
Orthochromatic films Sensitive to red spectrum
Small crystals, ____resolution, ____ speed. high , slow.
Large crystals, ____resolution, ____ speed. low, fast.
Thin emulsion layer provides ____ resolution and ____ speed. high, slow.
Thick emulsion layer provides ___ resolution and ___ speed. low, fast.
How films should be stored and under what conditions? Films should be stored on end, at a temperature of 20C (68F)or lower. The humidity must be maintained between 30-60%.
Subject Density thicker and denser body parts absorb more radiation, thus producing less image receptor exposure and vice versa.
Subject Contrast Is the degree of differential absorptions resulting from differing absorption characteristics of the tissues in the body.
Subject Detail The recorded detail is dependent on their position within the body and also the bosy's placement in relationship to the receptor.
Subject Distortion is the misrepresentation of the size or shape of the structure of interest.
Created by: 570419180