Physics chps 8-10
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| A radiographic image is a result of | differential absorption of primary x-rays that interact with underlying tissue composition of the anatomic area of interest
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| beam attenuation occurs when | primary x-ray beam loses energy as it interacts with anatomic tissues
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| t/f: x-rays have the ability to eject electrons (ionization) from atoms within anatomic tissue | true
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| ionization | ejection of electrons from atoms
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| 3 primary processes occur during x-ray interaction with anatomic tissue | absorption, transmission, scattering
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| scattering aka | compton
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| total absorption of the incoming x-ray photon is a result of | photoelectric effect
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| scattering of incoming x-ray photon is a result of | Compton effect
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| Scatter radiation reaching the IR provides...and creates...on the radiograpgh | no useful info; unwanted density/fog
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| Complete absorption of incoming x-ray occurs when it has enough energy to... | remove/eject an inner-shell electron
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| attenuation | reduction in energy of primary x-ray beam as it passes through anatomic tissue
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| Coherent scattering | incoming photon interacts with atom causing it to become excited, x-ray does not lose energy but changes direction
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| energy of coherent scattering | low energy, below diagnostic range
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| coherent aka | thompson or classical
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| coherent energy in kvp | 10 kVp or less
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| Compton effect | loss of energy of incoming photon when it ejects an outer-shell electron from atom. remaining lower-energy photon changes direction and may leave anatomic part
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| compton aka | scatter, recoil
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| differential absorption | some of x-ray beam is absorbed in tissue and some passes through(transmits) the anatomic part
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| exit radiation | attenuated beam leaves patient
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| exit radiation composed of | transmitted and scattered radiation
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| photoelectric effect has enough energy to... | remove(eject) inner shell electron.
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| higher kVp = ...scatter | more
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| photoelectron | ejected electron resulting from total absorption of photon during photoelectric effect interaction
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| remnant radiation aka | exit radiation
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| Scattering | some incoming photons are not absorbed, but instead lose energy during interactions with atoms comprising tissue and change direction and may leave anatomic part
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| does transmission radiation interact with atomic structures | no
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| results in process of image formation, whereby x-ray beam interacts with anatomic tissue and a portion of beam strikes IR | differential absorption
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| loss of some energy from xray beam as it passes through tissue being imaged | attenuation
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| process of removing an electron from an atom | ionization
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| when xray photon strikes an atom within tissue being imaged and loses all of its energy to an inner shell electron of that atom, the photon is said to have been... and undergone... | absorbed, photoelectric interaction
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| coherent regarding direction and interaction | changes direction, no interaction
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| when xray photon strikes an atom within tissue and loses only part of its energy to an outer shell electron of that atom, the photon is said to have been...and undergone... | scattered, compton interaction
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| photoelectric deals with ... shell | inner
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| t/f:coherent changes direction | true
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| outer shell electron that is ejected during compton interaction is aka | secondary electron, compton electron
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| can compton effect strike the IR, resulting in useful anatomic info | no
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| t/f: compton interaction can occur within all diagnostic xray energies | true
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| T/F: any time tissue is hit = scatter | true
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| T/F: compton interactions are most likely to occur in soft tissue as compared to bone | false, density does not matter
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| T/F: density does not matter with compton interactions | true
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| meV of pair production | 1.02 meV
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| meV of photodisintegration | 10 meV
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| interactions of low energy xrays (below diagnostic range) with tissue include: | coherent scattering
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| xray beam that leaves patient in direction of IR is often referred to as | exit radiation
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| unwanted density on a radiograph due to scatter radiation | fog (washes out image)
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| At higher kilovoltage, ... photon interactions occur, resulting in...transmission | fewer, increased
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| if kVp goes up, mAs... | divide by 2
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| if kVp goes down...%, mAs... | 15%, multiply by 2
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| efficiency of xray production increases as ... increase | kVp
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| penetrability of an xray beam | quality
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| beam quality is affected by | kVp and filtration
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| image contrast is affected by | beam quality/kVp
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| Half value layer of beam measures beam ... | quality
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| HVL is lowered by a decrease in ... | kVp
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| main purpose of added filtration | reduce patient dose
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| two primary forms of xray interaction in diagnostic range | compton scattering, photoelectric absorption
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| thompson aka | classical
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| outer shell electron is ejected and atom is ionized with ... interactions | compton
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| Xray interaction that involves ejection of K-shell electron | photoelectric
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| As kVp ... probability of photoelectric absorption ... | increases, decreases
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| complete absorption of incident xray photon with ... effect | photoelectric
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| ... occurs only at very high energies used in radiation therapy and nuclear medicine PET imaging | pair production
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| only at energies above 10 MeV ... can take place | photodisintegration
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| attenuation is caused by | absorption and scattering
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| negative contrast agent | air
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| barium is a good contrast agent because | of its high atomic #
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| at energies below 40 KeV, predominant xray interaction in soft tissue and bone is | photoelectric absorption
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| Find following: 200 mA, .05 sec, 70 kVp ... mA, .01 sec, 80 kVp | 200 mA x .05 sec = 10 mAs
kVp increases by 15%, mAs/2
mAs = 5
500 x .01 secs=5
answer = 500 mA
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| Find following: 400 mA, .06 sec, 80 kVp 200 mA, ... sec, 80 kVp | 400 mA x .06 sec = 24
answer = .12 sec
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| increase in kVp results in increase in | radiation quality
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| increase in mAs will increase ... | xray quantity
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| purpose of wedge filter | produce a uniform xray beam intensity at IR
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| purpose of adding filtration to an xray beam | remove low energy xrays
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| process that contributes most to the radiographic image | photoelectric effect
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| high kVp in chest xrays will increase/decrease contrast/patient dose or demonstrate spine? | decrease patient dose
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| radiographic quality is combination of | both visibility (photographic properties) and sharpness (geometric properties of recorded detail
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| visibility is aka | photographic properties
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| sharpness is aka | geometric properties
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| visibility of recorded detail is achieved by | proper balance of radiographic density and radiographic content
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| radiographic density -controlled by | the amount of oeverall blackness produced on image after processing
-miliamperage and exposure time selected
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| a change in mAs results in direct change in | radiographic density
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| to maintain density, milliamperage and ... have an inverse relationship | exposure time
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| if mA increases, sec ... to maintain density | decreases
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| ... changes the penetrating power of xray beam and has a direct effect on density | kilovotage
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| if kVp increase, scatter ... | increases
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| % of mAs needed to see changes on film | 30%
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| % of kVp needed to see changes on film | 15%
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| if SID increases, density ... -unless | decreases
-compensating a change on film
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| changing SID and/or film-screen speed requires an adjustment in ... to maintain density | mAs
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| increased film speed = ... density and ... resolution | increased density, decreased resolution
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| radiographic contrast is combined result of -affects ... of recorded detail | IR contrast and subject contrast
-visibility
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| a radiograph with few densities but great differences among them is said to have ... -described as ... | high contrast
-short scale contrast
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| a radiograph with a large number of densities but little differences among them is said to have ... -described as ... | low contrast
-long-scale contrast
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| kilovoltage has an inverse relationship with | radiographic contrast
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| high kVp will create an image with ... contrast and low kVp will create and image with ... contrast | low,
high
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| increasing amount of scatter radiation reaching image receptor creates ... on image and will decrease ... | fog,
contrast
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| exposure factors may need to be modified for ... patients | pediatric
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| increased collimation = ... density | decreased
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| thicker part = ... + ... decreased | density and contrast
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| film processing affects ... because ... is either too much or too little | contrast negatively, density
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| film speed increases, mAs ... and density ... | mAs decreases, density increases
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| kVp increases, contrast ... or more ... | decreases, more grays
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| total absorption | photoelectric affect
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| positive contrast agent | barium
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| more mAs = more ... | quantity/dose
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| if you decrease/increase distance, you need to decrease/increase | mAs
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| # of xrays in useful beam = ... | quantity
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| quantity proportional to | mAs
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| if distance decreases by 1/2, intensity goes up by ... | 4 times
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| intensity is always ... when distance is decreased | squared
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| if filter thickness increases, intensity ... | decreases
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| if quantity is doubled, optical density... | goes up by 2
(20 mAs -> 40 mAs)
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| intensity is aka | kVp
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| optical density is aka | mAs
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| if kVp increase by 15%, mAs increases by ... % | 100%
70 kVp, 20 mAs --> 80 kVp, 40 mAs
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| intensity formula | mAs1/mAs2 = d2/d1
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| beam quality affected by 2 | kVp, filtration
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| beam quality NOT affected by ... 2 | mAs, distance
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| image contrasted is affected by | kVp
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| quality improves by increased | beam filtration (eliminates lower energies)
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| if filtration is increased, quality ... and quantity ... | quality increases, quantity decreases
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| energy loss at coherent | none
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| coherent energy level | 10 kVp or less
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| coherent interaction | capture and release
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| interaction where atom is ionized (outer shell kicked out) | compton/recoil
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| T/F: with compton interaction, electron retains most of its energy | true
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| direction compton can be directed | any angle
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| if kVp increases, there is going to be less of ... interaction | photoelectric (absorption)
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| 2 interactions at a higher energy radiation than diagnostic | photodisintegration and pair production
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| photodisintegration occurs at ... energy level | 10 meV
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| pair production occurs at ... energy level | 1.02 meV
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| higher k-shell binding energy is directly proportional to what characteristic of atom | high atomic number
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| greatest mAs density in body | bone
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| image fog is caused by | compton
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| differential absorption depends on 3 | kVp, atomic number and mAs
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| attenuation is caused by | absorption and scatter
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| transmitted means | radiation that went through patient
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| xrays transmitted w/o ... contribute to image | interaction
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| absorbed xrays contribute to ... radiation | scatter
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| spatial resolution improves with | less motion/geometric blur
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| speed = less ... and more ... | less detail, more noise
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| density | overall blackening of a radiograph
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| mAs determines the ... that wil be produced | quantity (number) of xrays
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| an increase in mAs will result in an increase in | density
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| the controlling factor for density is ... because ... | mAs, because it affects density but not any other radiographic qualities
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| ... is directly proportional to density | mAs
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| in order to make a significant change in density, mAs should be increased/decreased by ... | increased by 100% or decreased by 50%
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| an increase in kVp will result in an ... in density because of | increase; more scatter
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| it only takes ... kVp to double density of a radiograph | 15%
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| ... determines intensity of xray beam | SID
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| an increase in SID will ... density | decrease
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| two types of filtrations | beam and compensating
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| beam filtration amount | 2.5 Al
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| beam filtration filters | low energy xrays from xray beam
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| beam filtration above 2.5 Al will result in | a decrease in density
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| compensating filter is designed to compensate for | differences in tissue thicknesses
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| an increase in the thickness of a compensating filter will result in ... in density | decrease
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| increased of distance does not change ... | kVp
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| ... distance = better detail | further distance
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| filtration measured in | millimeters of aluminum
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| amount of inherent filtration | .5 mm Al
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| inherent filtration found in | glass tube
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| anode heel effect | greatest intensity on cathode side of tube
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| body habitus | form of body
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| high contrast | radiograph with few densities but great differences among them
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| high contrast aka | short scale contrast
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| long scale contrast | radiograph with large number of densities but little differences among them
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| long scale contrast aka | low contrast
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| OID | object to distance distance
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| radiographic contrast can aka | grays
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| radiographic density | overall blackness produced on image after processing
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| short scale contrast | radiograph with few densities but great differences
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| short scale contrast aka | high contrast
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| SID | distance between source of radtiatin and IR
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| brightness aka | grays
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| changing kVp, etc. in digital imaging will only change contrast as it relates to | scatter radiation
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| few densities = ... scale contrast | short
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| several densities = ... scale contrast | long
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| total amount of filtration | 2.5 mm Al
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| if using barium you need to adjust kVp by ... it | increasing
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| ... kVp used with iodine contrast | 70 or below
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| if filament temperature increases, there is ... mAs | more
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| square law | mAs1/mAs2 =d1(squared)/d2(squared)
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| too much filtration cuts down on ... | useful xrays
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| with hardening, only ... xrays come through | high quality
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| trough filtration used for | chest xrays
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| more distance needs more ... but ... doesnt change | mAs, kVp
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