MED RAD FINAL EXAM Flashcards
Radiation is transmitted through
waves and particles
List radiation types
electromagnetic, acoustic, particulate, gravitational
List wave features
amplitude, frequency, wavelength, period
Explain amplitude
max strength of wave
Increase amplitude =
increase intensity
Explain frequency
number cycles per second (Hz) - number of times going up / down
Increase frequency =
increase intensity
Explain wavelength
distance between 2 same wave points
Shorter wavelength =
increase intensity, higher energy
Explain period
how long each wave cycle takes
Charges have an ________ field around them
electric
Moving charges create a _________ field
magnetic
Disturbance in a charge creates ____________ waves
electromagnetic
Explain “electric and magnetic fields are perpendicular to the direction of energy”
electric and magnetic fields travel horizontally and vertically down the wave at at 90 degree angle
Photons are the quantum form of ___________
EMR (electromagnetic radiation)
What properties do low E EMR have?
wave like properties
What properties do high E EMR have?
particle like properties
Explain purple / blue end of the EMR spectrum
High E, High frequency, shorter wavelength
Explain red end of the EMR spectrum
low E, low frequency, longer wavelength
EMR travels at?
speed of light in a vacuum
waves and C (speed of light) formula
C = f x wavelength
Energy formula
E = h x f
Most of the x-ray beam is high or low E photons?
low E photons
Two processes that create xrays
characteristic and brems radiation
characteristic radiation process
electron hits inner shell electron, knock it out of orbit, outer shell electron drops into vacancy (usually L), releases E in form of x-ray photon
characteristic radiation only affected by what?
atomic number
brems produces mostly ________ photons
low energy
Photons produce what?
EMR
Energy travels as _________ waves
sinusodial
Electric and magnetic fields are _________ to the direction of energy
perpendicular (90)
What does ionize have the ability to do?
remove electrons from atoms (ex. CS and PE, gamma, x-ray) - creates ions
Why is coherent scatter non-ionizing?
because it doesn’t have enough energy to remove electrons from atoms - it’s LOW E
What is wave like particle duality
waves can exhibit particle-like properties while particles can exhibit wave-like properties
c = __ x ___ ^ m/s
c = 3 x 10^8 m/s
Order of colours in EMR
purple, blue, green, yellow, orange, red
List wavelike interactions:
reflection, refraction, diffraction, interference
Explain reflection
Bounces off surface, changes direction (not absorbed)
Explain refraction
Change in direction from speed (ex. straw bending in water)
Explain diffraction
wave bends around boarders to create pattern
Explain interference
Waves add together (constructive) OR cancel out (destructive)
Do x-rays diffract?
yes (atomic planes of a crystal cause an incident beam of X-rays to interfere with one another)
Define quantum and example
smallest unit of something (photon = x-rays)
What occurs during excitation?
excites electron to higher E level, no charge change - non ionizing
Are high or low energy photons more harmful?
low, because high E photons are more likely to penetrate
Explain beam spectra features: max E
highest energy possible (furthest right), depends on kvp
Explain beam spectra features: low E
lowest energy possible (furthest left), filtration (filters out low E), mostly produced by brems
Explain beam spectra features: avg E (effective beam E)
affected by waveform, atomic number, filtration - 1/3-1/2 of peak - tallest peak
Explain beam spectra features: line spectra
depends on atomic number, contsant E level, shouldn’t move until atomic number changes - fixed E
In a graph for beam/emission spectra look for changes in:
height, avg E, line spectrum, max / min
Explain emission spectra changes involving: kvp
shift on the “x” axis of graph - increase in kvp causes increased photons / max E / avg E
Explain emission spectra changes involving: ripple
Avg E / height change - decreased ripple causes increased photons / avg E (low ripple has MORE energy = higher height). Shifts left (increased ripple = decreased photons)
Explain emission spectra changes involving: filtration
increased filtration causes decreased photons, increased avg E (shifts to the right)
Explain emission spectra changes involving: mA
affects curve height (change will occur in the same spot - no shift), increase mA causes increased photons (equal increase)
Explain emission spectra changes involving: atomic number
line spectrum (char): increased Z causes increased photons / avg E. Brems: avg E to the right as atomic number increases
Max E on a spectra graph only moves on x axis if what changes?
kvp
What does filtration help with?
improving image quality by decreasing low E photons
Avg E of 100 kev
100 / 2 and 100 / 3 = 33 to 50
Larger area under graph =
larger intensity
K BE and L BE tungsten
69 and 12
What percent of beam is characteristic radiation?
0-10%
Electron must have at least ______ to dislodge in char rad
70
Anything less than 69 =
no char rad
Characteristic radiation only exist at ________ levels
certain energy
K - shell BE is high or low E?
high E
How many possibilities with char rad?
5
Brems is _____ of the beam
90%
What percent becomes xrays and heat?
x-rays = 1%, heat = 99%
What do electrons do?
orbit around the nucleus
Define binding energies
E required to remove an electron from atom
AEC location in mammo and why?
After IR ; allows decreased OID with breast
What decreases anode heel effect in mammo?
tube tilt - allows for maintained CR + SR
Mixed target and filter in mammo is what kind of radiation?
brems rad
same target and filter in mammo is what kind of radiation?
char rad
Why do we use molybdenum in mammo?
low atomic number, spike at 17-19 kev
Energy molybdenum and rhodium?
Mo = 17-19 kev and Ro = 20-23 kev
Grounded metal tube used in mammo prevents?
off focus radiation
Most of mammo beam is?
char rad
SR factors in mammo
compression, small FS, AEC location (after), IR (direct), grounded metal tube (decrease off focus rad), OID
CR factors in mammo
Compression, beam E, grid, tube orientation (Chest-cathode, BT-anode), tube tilt
Magnification mode factors in mammo
No grid (uses air gap technique), done to look at a. certain area - middle is sharper, uses increased OID and small FS - increased SR (pixels) / CR (photons)
Increase or decrease PT dose mammo: compression
decrease (compression decreases thickness so less penetration / kvp needed)
Increase or decrease PT dose mammo: Beam E
increase
Increase or decrease PT dose mammo: tomosynthesis
increase (multiple images at once)
Increase or decrease PT dose mammo: mag mode
same - because no grid is used so it balances out
Increase or decrease PT dose mammo: grid
increase (higher exp time needed to compensate)
Increase or decrease PT dose mammo: short SID
increase (higher intensity - BT)
Does shorter SID / small angle increase or decrease anode heel effect?
Increase (tilt is used)
increased mAs = ________ pt dose
increased (longer exp)
What affects beam E in mammo?
using Mo / Ro, kvp, filtration
Low E interacts with __________
molecules & atoms
Medium E (diagnostic) interacts with ____________
electron
High E (NOT in diagnostic) interacts with __________
nucleus (ignores electrons)
Define attenuation - examples
beam / rad intensity loss - absorption and scatter
Chest has _______ natural subject contrast
high (high kvp to smooth it out)
Breast has _______ natural subject contrast
low (low kvp can help increase SC)
In image, CS shows difference in _______
density
In image, PE shows difference in _______
atomic number and density
Magic number for bone and soft tissue
Bone: 40, ST: 20
What occurs above / below the magic # for bone and soft tissue?
above 40/20 = scatter, below 40/20 = absorption
Magic number where both CS and PE have a chance of occuring
at 80 kvp they have a 50/50 chance of occuring
what occurs above / below the magic # for CS/PE?
bwloq 80 = more chance of absorption (grey shades), above 80 = more chance of scatter
High kvp = _______ absorption
decreased
Increase Z = _______ PE
increased
Increased E = _______ CS/PE
decreased
Other name(s) for CS?
modified scatter
Other name (s) for coherent scatter?
unmodified, thomson, rhyleigh, classical
Energy CS is left with after interaction?
66% (2/3)
Energy of a photon formula
KE = hf - BE (Energy of the photon minus the BE)
Explain occurrence of k-edge
Sudden increase in absorption of x-rays that occur when the E is just above the BE
Greatest probability of absorption (PE) happening
Photon E just above BE, none if it’s below
PE interaction
x ray photon comes in, ionizes atom - inner k-shell electron ejected, all energy absorbed, outer shell electron drops in, secondary characteristic radiation & photoelectron created
Probability of photoelectron effect occurring formula atomic number and energy
𝑃𝐸 = 𝑍^3/𝐸^3
No chance of absorption when?
photon E below BE
How does PE affect the patient?
All E from interaction goes to PT (absorbed) - so photon has lower E after interaction
End products for PE
photoelectron and secondary char rad
End products for coherent scatter
scattered photon
End products for CS
ion pair (positive atom, compton electron) and scattered photon
CS interaction
X-ray photon comes in, Ionizes atom, knocks OUTER shell electron out (CAN be inner shell – but usually outer), changes direction (direction change depends on E), loses some energy, creates ion pair and scattered photon
Coherent scatter affect on pt?
none - no tissue damage occurs - E is kept by atom
Coherent scatter interaction
x-ray photon comes in, EXCITES atom, changes direction, scattered photon created ; maintains all it’s E (same E, freq, wavelength)
How rare is coherent scatter?
rarely occurs - less than 5%
Scatter effect on image?
decreased quality - grain / decreased contrast
Pair production interaction
photon comes in, interacts with nucleus, nucleus rips it into two, creates positron and electron - E level 1.02 mEv
Photodisintgration interaction
photon comes in, interacts with nucleus, nucleus releases apart of itself (nuclear fragment) - E level 10 mEv
Probability of coherent scatter occurring?
Higher Z / low E - when you have wayyyyyy higher BE than photon E (so, not with human tissue)
What does PE magnify image wise?
Subject contrast - able to show detail / differences in tissues (lower kvp use)
What do each CS / PE show differences in
CS = density, PE = atomic number and density
Probability of CS occuring?
when photon E much higher than BE
Difference in x-ray photos are mostly due to
absorption
What happens once k-edge is hit?
huge spike of absorption
As E increases, what happens to CS/PE?
both decrease
Why lower kvp with abdomen than chest ?
want to heighten subject contrast like the kidneys / bowels
When imaging the chest, especially with a female patient, want to use a high or low kvp? why?
With a high kvp the breast would show up grey like other soft tissue
Why does mammo use low kvp?
Less penetration power needed because breast is just ST/Fat, and low kvp allows for more absorption = increased subject contrast to show details in breast
Mo BE?
20 kev (will allow photons in JUST below - 17-19)
KeV best for imaging breast?
17-24 kEv
K-edge filters all but ______ with Mo
17-19kev
Rhodium BE
23 kev
K-edge filters all but ______ with Ro
20-23 kev
Why is char rad needed for k-edge to occur?
because char rad is what gives it the spike
Smaller space charge in mammo why?
because the cathode and anode are closer together
Chances of space charge occurring _______ with low kvp
increases
The shorter distance with the cathode and the anode in mammo allows for?
less intensity loss in the beam (attenuation)
Con of short SID distance in mammo?
increased pt dose, increased anode heel, decreased sharpness (beam divergence)
How to decrease anode heel effect in mammo?
tube tilt - 20-24 degrees - allows SR to be maintained, and having chest wall at cathode end, BT at anode end
AEC location in mammo
after IR
Use of ______ FS size in mammo allows for ______
small, better SR / detail
Digital tomosynthesis in mammo increases ____ resolution
CR
Can PE cause new ionizations?
yes
PE is made up of
char rad
PT dose with PE?
ALL E to patient, so high pt dose
Why is subject contrast higher with PE?
because absorption is a factor with subject contrast (density/thickness), the more absorbed, the better the subject contrast
Why does chances of absorption decrease with increased energy?
because the energy of the photons are too high to be absorbed
Can coherent scatter cause ionization ?
no, too low of E - just excites (non ionizing)
Decreased E in CS after interaction leads to
longer wavelength, decreased freq, decreased E
Probability of PE occurring density formula
𝑃𝐸 = density^1
Probability of CS occurring density formula
CS = d/E^1
As E in increases, probability of PE decreases _______ and CS decreases _______
PE - sharply, CS - gradually
Can CS cause new ionizations?
Yes
Can pair production cause new ionizations?
yes
Can photodisintegration cause new ionizations?
yes
With tungsten K shell BE 69, what would happen with photons with 60 kev?
they’d likely be absorbed (and too high for L shell)
Will CS graph have k-edge?
no, only PE (bc k-edge is absorption)
How to calculate avg E? kvp
multiply kvp value by 2 and 3, any number in between is the Avg E
How to figure out “what is the KE of the photoelectron”
E - BE (KE = hf - BE)
If small diff in density, and very large diff in atomic number, which would show contrast? CS, PE, or both
PE (atomic number high) - both if density is larger diff
Diff in photo mostly due to
absorption
Why increase kvp with chest?
because chest has high natural subject contrast - so high kvp helps smooth it out, and higher kvp with female helps penetrate BT / show grey values
Is mammo mostly PE or CS?
PE
Probability of k-edge with L-shell
with very low E photons - decreases as E increases
What does a filter allow for?
only a narrow range of photons through
photons transmitted vs absorbed
Transmitted: X-rays pass through the material with little or no energy loss.
Absorbed: X-rays transfer all of their energy to the material and do not pass through
What photons will be transmitted and what photons will be absorbed, with k-edge?
absorbed: photons with E just above the BE
transmitted: photons with E JUST below BE
with K shell, ______ probability if below BE
zero (ex. 68)
with K shell, _______ probability if above BE
greatest
Does human tissue k-edge?
no, too low
Ex. 80 kvp beam – only photons between 59-68 in the beam, meaning?
15% (80x0.15 = 12, 80-12 = 68)
Will k-edge occur with contrast?
yes, because high Z
calculate “kvp range”
BE x 2, BE x 3 = number in between
Faster IR’s are better at ________
absorption (requires less mAs)
High atomic number = _______ absorption
increased
Heavy element filters absorb _______ E photons and lets in those _______ the BE
low, just under
For IR to produce an image, must ______ radiation
absorb
Can use a lower mAs with ______, which has better absorption and patient dose
rare earth
Examples of ionizing radiation
gamma, xrays
Examples of non-ionizing
Radiowaves, microwaves
are high or low energy photons more penetrating?
high
Most of x-ray beam is ________ E photons
low
Purpose of fluorescence ?
emits x-rays after interaction
Name of char rad depends on what?
depends on the shell being filled
All mean the same thing with: char rad
discrete, line, homogenous, monoenergetic
10% of beam is char rad at what kvp
70-150 kvp
Differences between char rad & PE
PE - all E absorbed to patient, and involves photon
Char rad - occurs in the tube, involves electrons
How are x-rays released in brems rad?
deceleration
With brems, deceleration closer to the nucleus results in what?
Higher energy x-ray photon and more speed loss
With brems, deceleration further from the nucleus results in what?
Lower E x-ray photon and less speed loss
Explain Brems rad interaction
x-ray electron pass by nucleus, change direction
Mean the same thing in Brems:
polyenergentic, heterogeneous, continuous
Brems end product
Brems x-ray photon
No char rad produced below ______
70 kvp (below 70kvp would be brems)
Area under graph = _______
intensity
Photons in brems can exist at _______
any E lvl
In order for brems to hit peak, has to what?
hit nucleus - which is rare
Determining peak is
1/3-1/2
Max E is determined by
kvp
Decrease ripple =
Increased E / photons
