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Physics chps 8-10

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
beam attenuation occurs when primary x-ray beam loses energy as it interacts with anatomic tissues
t/f: x-rays have the ability to eject electrons (ionization) from atoms within anatomic tissue true
ionization ejection of electrons from atoms
3 primary processes occur during x-ray interaction with anatomic tissue absorption, transmission, scattering
scattering aka compton
total absorption of the incoming x-ray photon is a result of photoelectric effect
scattering of incoming x-ray photon is a result of Compton effect
Scatter radiation reaching the IR provides...and creates...on the radiograpgh no useful info; unwanted density/fog
Complete absorption of incoming x-ray occurs when it has enough energy to... remove/eject an inner-shell electron
attenuation reduction in energy of primary x-ray beam as it passes through anatomic tissue
Coherent scattering incoming photon interacts with atom causing it to become excited, x-ray does not lose energy but changes direction
energy of coherent scattering low energy, below diagnostic range
coherent aka thompson or classical
coherent energy in kvp 10 kVp or less
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
compton aka scatter, recoil
differential absorption some of x-ray beam is absorbed in tissue and some passes through(transmits) the anatomic part
exit radiation attenuated beam leaves patient
exit radiation composed of transmitted and scattered radiation
photoelectric effect has enough energy to... remove(eject) inner shell electron.
higher kVp = ...scatter more
photoelectron ejected electron resulting from total absorption of photon during photoelectric effect interaction
remnant radiation aka exit radiation
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
does transmission radiation interact with atomic structures no
results in process of image formation, whereby x-ray beam interacts with anatomic tissue and a portion of beam strikes IR differential absorption
loss of some energy from xray beam as it passes through tissue being imaged attenuation
process of removing an electron from an atom ionization
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
coherent regarding direction and interaction changes direction, no interaction
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
photoelectric deals with ... shell inner
t/f:coherent changes direction true
outer shell electron that is ejected during compton interaction is aka secondary electron, compton electron
can compton effect strike the IR, resulting in useful anatomic info no
t/f: compton interaction can occur within all diagnostic xray energies true
T/F: any time tissue is hit = scatter true
T/F: compton interactions are most likely to occur in soft tissue as compared to bone false, density does not matter
T/F: density does not matter with compton interactions true
meV of pair production 1.02 meV
meV of photodisintegration 10 meV
interactions of low energy xrays (below diagnostic range) with tissue include: coherent scattering
xray beam that leaves patient in direction of IR is often referred to as exit radiation
unwanted density on a radiograph due to scatter radiation fog (washes out image)
At higher kilovoltage, ... photon interactions occur, resulting in...transmission fewer, increased
if kVp goes up, mAs... divide by 2
if kVp goes down...%, mAs... 15%, multiply by 2
efficiency of xray production increases as ... increase kVp
penetrability of an xray beam quality
beam quality is affected by kVp and filtration
image contrast is affected by beam quality/kVp
Half value layer of beam measures beam ... quality
HVL is lowered by a decrease in ... kVp
main purpose of added filtration reduce patient dose
two primary forms of xray interaction in diagnostic range compton scattering, photoelectric absorption
thompson aka classical
outer shell electron is ejected and atom is ionized with ... interactions compton
Xray interaction that involves ejection of K-shell electron photoelectric
As kVp ... probability of photoelectric absorption ... increases, decreases
complete absorption of incident xray photon with ... effect photoelectric
... occurs only at very high energies used in radiation therapy and nuclear medicine PET imaging pair production
only at energies above 10 MeV ... can take place photodisintegration
attenuation is caused by absorption and scattering
negative contrast agent air
barium is a good contrast agent because of its high atomic #
at energies below 40 KeV, predominant xray interaction in soft tissue and bone is photoelectric absorption
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
Find following: 400 mA, .06 sec, 80 kVp 200 mA, ... sec, 80 kVp 400 mA x .06 sec = 24 answer = .12 sec
increase in kVp results in increase in radiation quality
increase in mAs will increase ... xray quantity
purpose of wedge filter produce a uniform xray beam intensity at IR
purpose of adding filtration to an xray beam remove low energy xrays
process that contributes most to the radiographic image photoelectric effect
high kVp in chest xrays will increase/decrease contrast/patient dose or demonstrate spine? decrease patient dose
radiographic quality is combination of both visibility (photographic properties) and sharpness (geometric properties of recorded detail
visibility is aka photographic properties
sharpness is aka geometric properties
visibility of recorded detail is achieved by proper balance of radiographic density and radiographic content
radiographic density -controlled by the amount of oeverall blackness produced on image after processing -miliamperage and exposure time selected
a change in mAs results in direct change in radiographic density
to maintain density, milliamperage and ... have an inverse relationship exposure time
if mA increases, sec ... to maintain density decreases
... changes the penetrating power of xray beam and has a direct effect on density kilovotage
if kVp increase, scatter ... increases
% of mAs needed to see changes on film 30%
% of kVp needed to see changes on film 15%
if SID increases, density ... -unless decreases -compensating a change on film
changing SID and/or film-screen speed requires an adjustment in ... to maintain density mAs
increased film speed = ... density and ... resolution increased density, decreased resolution
radiographic contrast is combined result of -affects ... of recorded detail IR contrast and subject contrast -visibility
a radiograph with few densities but great differences among them is said to have ... -described as ... high contrast -short scale contrast
a radiograph with a large number of densities but little differences among them is said to have ... -described as ... low contrast -long-scale contrast
kilovoltage has an inverse relationship with radiographic contrast
high kVp will create an image with ... contrast and low kVp will create and image with ... contrast low, high
increasing amount of scatter radiation reaching image receptor creates ... on image and will decrease ... fog, contrast
exposure factors may need to be modified for ... patients pediatric
increased collimation = ... density decreased
thicker part = ... + ... decreased density and contrast
film processing affects ... because ... is either too much or too little contrast negatively, density
film speed increases, mAs ... and density ... mAs decreases, density increases
kVp increases, contrast ... or more ... decreases, more grays
total absorption photoelectric affect
positive contrast agent barium
more mAs = more ... quantity/dose
if you decrease/increase distance, you need to decrease/increase mAs
# of xrays in useful beam = ... quantity
quantity proportional to mAs
if distance decreases by 1/2, intensity goes up by ... 4 times
intensity is always ... when distance is decreased squared
if filter thickness increases, intensity ... decreases
if quantity is doubled, optical density... goes up by 2 (20 mAs -> 40 mAs)
intensity is aka kVp
optical density is aka mAs
if kVp increase by 15%, mAs increases by ... % 100% 70 kVp, 20 mAs --> 80 kVp, 40 mAs
intensity formula mAs1/mAs2 = d2/d1
beam quality affected by 2 kVp, filtration
beam quality NOT affected by ... 2 mAs, distance
image contrasted is affected by kVp
quality improves by increased beam filtration (eliminates lower energies)
if filtration is increased, quality ... and quantity ... quality increases, quantity decreases
energy loss at coherent none
coherent energy level 10 kVp or less
coherent interaction capture and release
interaction where atom is ionized (outer shell kicked out) compton/recoil
T/F: with compton interaction, electron retains most of its energy true
direction compton can be directed any angle
if kVp increases, there is going to be less of ... interaction photoelectric (absorption)
2 interactions at a higher energy radiation than diagnostic photodisintegration and pair production
photodisintegration occurs at ... energy level 10 meV
pair production occurs at ... energy level 1.02 meV
higher k-shell binding energy is directly proportional to what characteristic of atom high atomic number
greatest mAs density in body bone
image fog is caused by compton
differential absorption depends on 3 kVp, atomic number and mAs
attenuation is caused by absorption and scatter
transmitted means radiation that went through patient
xrays transmitted w/o ... contribute to image interaction
absorbed xrays contribute to ... radiation scatter
spatial resolution improves with less motion/geometric blur
speed = less ... and more ... less detail, more noise
density overall blackening of a radiograph
mAs determines the ... that wil be produced quantity (number) of xrays
an increase in mAs will result in an increase in density
the controlling factor for density is ... because ... mAs, because it affects density but not any other radiographic qualities
... is directly proportional to density mAs
in order to make a significant change in density, mAs should be increased/decreased by ... increased by 100% or decreased by 50%
an increase in kVp will result in an ... in density because of increase; more scatter
it only takes ... kVp to double density of a radiograph 15%
... determines intensity of xray beam SID
an increase in SID will ... density decrease
two types of filtrations beam and compensating
beam filtration amount 2.5 Al
beam filtration filters low energy xrays from xray beam
beam filtration above 2.5 Al will result in a decrease in density
compensating filter is designed to compensate for differences in tissue thicknesses
an increase in the thickness of a compensating filter will result in ... in density decrease
increased of distance does not change ... kVp
... distance = better detail further distance
filtration measured in millimeters of aluminum
amount of inherent filtration .5 mm Al
inherent filtration found in glass tube
anode heel effect greatest intensity on cathode side of tube
body habitus form of body
high contrast radiograph with few densities but great differences among them
high contrast aka short scale contrast
long scale contrast radiograph with large number of densities but little differences among them
long scale contrast aka low contrast
OID object to distance distance
radiographic contrast can aka grays
radiographic density overall blackness produced on image after processing
short scale contrast radiograph with few densities but great differences
short scale contrast aka high contrast
SID distance between source of radtiatin and IR
brightness aka grays
changing kVp, etc. in digital imaging will only change contrast as it relates to scatter radiation
few densities = ... scale contrast short
several densities = ... scale contrast long
total amount of filtration 2.5 mm Al
if using barium you need to adjust kVp by ... it increasing
... kVp used with iodine contrast 70 or below
if filament temperature increases, there is ... mAs more
square law mAs1/mAs2 =d1(squared)/d2(squared)
too much filtration cuts down on ... useful xrays
with hardening, only ... xrays come through high quality
trough filtration used for chest xrays
more distance needs more ... but ... doesnt change mAs, kVp
Created by: dina11