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X-ray phisics 3
Question | Answer |
---|---|
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. |