Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Radiation Sciences 1 > Unit 2 > Flashcards

Unit 2 Flashcards

You may prefer our related Brainscape-certified flashcards:
USMLE® Step 1 flashcards
1
Q

What are the 3 types of support for X-ray tube?

A

ceiling
floor
C-arm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the ceiling support system?

A

most frequently used
2 perpendicular sets of ceiling mounted rails
telescoping column

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the floor mounted support system?

A

single column with rollers
allows for limited vertical, transverse and longitudinal movement
can be used with either table or wall Bucky
makes cross table difficult

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the C-arm support system?

A

interventional radiography suites
image receptor and tube connected
flexible movement with limited SID
U-arm variant for X-ray

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does X-ray housing provide?

A

radiation protection
electrical protection
thermal protection
physical protection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does the housing provide radiation protection?

A

lead lined
window allows useful radiation to escape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does the housing provide electrical protection?

A

high voltage receptacles
glass and oil - makes sure electricity is contained

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does the housing provide thermal protection?

A

oil
cooling fan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is the physical housing around the X-ray tube important?

A

glass is fragile
casing protects against bumps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the glass tube?

A

contains cathode and anode
Pyrex - high heat capacity and an insulator
Vacuum - no collisions and prevents oxidation of electrodes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a metal tube used for?

A

part or all of the is replaced by metal
on newer high capacity x-ray units
less tube wear, longer lifespan
reduces the chance of arcing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the filament of the cathode?

A

a tungsten coil - good e emitter
1-2% thorium - better e emitter but radioactive
approx 2mm diameter
1-2cm length
different length for different focal spot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why use Tungsten?

A

melting point of 3410C
prevents the wire from melting
low vapour pressure
does not easily evaporate
less vaporization occurs at high temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is thermionic emission?

A

current creates heat
heat gives more energy to electrons
electrons can escape binding forces
1st stage of the switch - hot current starts making an electron cloud

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does thermionic emissions work?

A

needs to reach threshold to emit 2200C
after threshold, small filament current increase causes a large tube current increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the danger of thermionic emission?

A

too much heat can cause evaporation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a space charge?

A

electrons form cloud around filament
space charge is held in place
- negative electrons repel each other
- filament becomes “positive”
- equilibrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is a compensation circuits?

A

Ensures mA is what we chose
mA can change depending on what kVp we select

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How does compensation circuit work with high kVp?

A
  • easy to pull mA across tube
  • lowers filament heating current
  • lowers space-charge size
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does compensation circuit work with low kVp?

A
  • much harder to pull mA across tube
  • increase filament heating current
  • increase space charge size
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the difference between the filament current and tube current?

A

Filament current - creates space charge and prep button
Tube current - allows mA to flow across tube and exposure button

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the focusing cup?

A

supports filaments
made of nickel because it is a good conductor but not a good thermionic emitter
negatively charged
focuses electrons to target focal spot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are dual focal spots?

A

focusing cup holds 2 filaments
one for each focal spot size
- small: 0.1-1mm, lower mA, higher resolution
- large: 0.3-2mm, higher mA, lower resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Selecting mA

A

mA has to be selected in “steps” and proportional to filament current
small focal spot: uptown 300 mA
large focal spot: over 400 mA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What happens when you increase the kVp?

A

Increases energy of photons
Increases the number of photons
Does NOT change the number of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What does the anode do?

A

X-ray production
supports the target
conducts current
dissipates heat
stationary or rotating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is a stationary anode?

A

Target does not move
need low parameters
energy localized to one area
stem is copper
- high thermal capacity
- high conductivity
- low melting point
target is tungsten

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the Tungsten target?

A

made of tungsten (W)
High atomic number - good at producing X-rays
High melting point
High thermal conductivity
Low vapourization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is target damage?

A

excessive heat causes damage
heat concentrated onto small area
unequal thermal expansion and concentration causes pitting
Factors (tube ratings): mA, time, kVp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is a rotating anode?

A

has better heat dissipation because of rotation
Components: disc, focal track, stem, rotor, stator
target made of tungsten and rhenium (10%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are the elements of the anode disc backing?

A

molybdenum and carbon
Lessening thermal conductivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the stem of the anode?

A

connects disc to rotor
made of molybdenum - poor heat conductor
thin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is the rotor of the anode?

A

made of copper - high conductivity
rotates on bearings

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the stator of the anode?

A

causes rotor to spin (no wires)
>3000 rpm, upto 12000 rpm - higher rotation has better heat dissipation
coast time of around 60s - coasting to a stop, no braking

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what type of motor is the rotor and stator?

A

induction motor
generator and motor principle stimultaneously
electromagnetic induction

36
Q

What is tube aging?

A

Over time the different parts of the x-ray tube wear down
- filament
- anode
- bearings
higher exposure ratings and longer prep times cause wear faster

37
Q

What causes filament wear?

A

caused by: high mA and longer prep
Consequences: tungsten plating on tube can cause arcing (may shatter the tube)
filament may break

38
Q

What causes anode wear?

A

causes: uneven thermal expansion and high exposure ratings (mA and kVp)
Consequences: pitting and unequal x-ray intensity

39
Q

Difference of rotating vs stationary targets for heat dissipation?

A

rotating has 500x heat capacity

40
Q

What causes bearing wear?

A

causes: heavy use and longer prep
Consequences: slower rotation (more pitting) and “grinding noise”

41
Q

What causes housing damage?

A

causes: physical damage and overheating
Consequences: oil leakage - things get hotter and then the tube can get more damaged

42
Q

How to prevent tube wear?

A

lower techniques, shorter preps
warm up the tube
- help prevent the anode damage
- procedure varies between manufacturers

43
Q

What factors affect tube ratings?

A

focal spot size
rotation speed
disk diameter (larger = better ratings)
waveform
segmented/grooved anode
metal tube (no fear of tungsten evaporation)

44
Q

Heat storage capacity

A

how many exposure you can do without cooling
- important for bearings

45
Q

What are heat units?

A

HU = kVp x mAs

46
Q

Heat units/second

A

amount of electrons emitted per second
energy of electrons hitting target per second
more important for filament and target
HU/s = kVp x mA

47
Q

What is an anode cooling chart?

A

shows the heat capacity of the anode
shows the length of time to completely cool
- cools very rapidly at first then slows down
only one chart per machine

48
Q

how does the tube cool down?

A

tube is in contact with oil to dissipate heat
- usually just the end of the rotor

49
Q

What is a rotating envelope tube?

A

entire tube spins, not just anode
anode in contact with oil - better heat dissipation
external bearings and motor
don’t have to worry about envelope tube

50
Q

What is the purpose of beam restriction?

A

patient safety
image quality

51
Q

how does beam restriction impact patient safety?

A

protects patients from radiation
smaller field size - less tissue irradiated
less energy absorbed by patient
lowers dose

52
Q

How does beam restriction impact image quality?

A

helps image contrast
less scatter
less tissue irradiated
higher subject contrast
improves image quality

53
Q

What was the start of the aperture diaphragm?

A

first used around 1899 by Dr. William Rollins (father of radiation protection)
Lead plates with holes cut in them
- designed for specific film sizes
- constricted the size of the beam

54
Q

use of cones and cylinders

A

simple lead shapes inserted into diaphragm
reduce more of the beam because of increased length
further improved image sharpness
downside: make the xray field circular while the plates were rectangular

55
Q

What is a variable aperture or light beam collimator?

A

what we use today
multiple levels of lead shutters to restrict beam more effectively (2-3 shutters)
lightbulb and mirror to represent x-ray field

56
Q

what do the different sets of shutters do?

A

first set - reduce off focus radiation
second set - allow field size/shape selection

57
Q

correlation between shutter distance and blur

A

lowe shutters = less blur

58
Q

what angle must the mirror be at inside the tube??

A

45 degrees

59
Q

what happens if the bulb and focal spot are not equal distance from the mirror?

A

bulb too close - xray beam would be smaller than light field
bulb too far - xray beam would be larger than the light field

60
Q

what percent of SID can misalignment be?

A

2%

61
Q

What is positive beam limitation?

A

limits the size of the collimation to the size of the IR

62
Q

What is a collimation scale?

A

for when positive beam limitation is not available and you can’t see the IR
the dials have notations for different sizes at different SID’s

63
Q

how is the diverging beam created?

A

by isotropic emission

64
Q

How does the diverging beam affect the image?

A

magnification
distortion
- focal spot blur
inverse square law for intensity
anode heel effect
these affects are not always detrimental

65
Q

Magnification

A

caused by diverging beam
outer portion of beam makes the object appear larger
affected by SID and SOD/OID

66
Q

magnification factor

A

how much larger the object appears in the image
Magnification factor = SID/SOD

67
Q

why is magnification useful

A

can be used to increase object size
better than zooming in
- more pixels per area of anatomy

68
Q

How is distortion caused

A

by diverging beam
- unequal magnification of object
changes the shape of the object
- elongation
- foreshortening
affected by SID, OID, object position and thickness of object

69
Q

how is foreshortening caused

A

object is angled but IR is flat

70
Q

how is elongation caused

A

object is parallel to IR, but central ray is angled
object is parallel to central ray, but IR is angled
causes object to be stretched out

71
Q

when do you use your angle to your advantage

A

bisecting angle method
- reduce distortion
- angle of central ray to IR = 1/2 angle of object to CR
superimpositions
- two objects on top if each other
- use angle to seperate

72
Q

focal spot blur

A

caused by diverging beam AND multiple point sources
edges of object hit by x-rays from multiple sources
creates penumbra
- geometric unsharpness

73
Q

blur prevention

A

longer SID
shorter OID
smaller focal spot size
- less point sources

74
Q

Inverse square law

A

caused by diverging beam
as you get farther from the source, more and more of the diverging beam misses the object
I1/I2 = (d2/d1)^2

75
Q

Large focal spot pros and cons

A

pros
- more area to be hit by electron beam
- less pitting of target surface
- higher ratings
cons
- more point sources
- more blur

76
Q

small focal spot pros and cons

A

pros
- sharper image
- less blurring
cons
- lower ratings
- more easily damaged

77
Q

what is the line focus principle

A

best of both worlds
use angle to achieve large actual focal spot
- high ratings
AND small effective focal spot
- less blur

78
Q

actual focal spot

A

large area to receive mA
- can take more heat and dissipate it better
rectangular in shape
point sources are farther apart
- larger penumbra

79
Q

effective focal spot

A

focal spot as seen from the POV of IR
square shape
point sources are closer together
- better spacial relation

80
Q

Anode angle

A

angle is from vertical
usually 12-17%
- 45 degrees = incident electron beam size
- <45 degrees = effective size is smaller than incident
- >45 degrees = effective size is larger than incident

81
Q

Same size, different angles

A

large angle
- shallow slope
- larger effective size
smaller angle
- steeper slope
- smaller effective size

82
Q

field size

A

smaller angles give us smaller field sizes

83
Q

On what images would a small angle be detrimental?

A

larger pieces of anatomy

84
Q

Anode heel effect

A

caused by angled target
some photons travel through the target itself
- some attenuation happens
- lower intensity
happens more with steeper angles
lowers intensity specifically at the anode side
intensity is unaffected at the cathode side

85
Q

when do you use the anode heel effect

A

can act like a filter
align anode to thinner portion of anatomy
T-spine
abdomen

86
Q

how to reduce the anode heel effect

A

longer SID
smaller field sizes

87
Q

biangular anodes

A

some anodes have 2 different angles
chooose either one depending on if your need the sharper image or larger field

Medical Radiation Sciences 1 (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions