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Skin Radiation therapy > CT sim/ Imaging > Flashcards

CT sim/ Imaging Flashcards

1
Q

cathode is the ____ part of the xray tube

A

negative

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2
Q

abided us ___ part of the xray tube

A

positive

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3
Q

what are the portions of the cathode

A

filament and focusing cup

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4
Q

what is filament made of

A

its a small coil of tungseten wire with a high melting point

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5
Q

focusing cup

A

the - charge of thr focusing cup can help direct e towsrds the anode in a or linear path

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6
Q

do e go from anode to cathode or cathode to anode

A

cathode to anode (- to +)

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7
Q

what are the prts of the anode

A

line focus principle, composition and target

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8
Q

the target in the anods is aka

A

focal spot

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9
Q

i am the part of the CT where photons start to fan out in a divergent path

A

the target of the anode

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10
Q

what is done to overcome extra heat production of a small focal spot

A

the line focus principle- the target is angled at 7-20 degrees to account for extra heat

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11
Q

anode, cathode, filament, focusing cup, target are components of what machine

A

CT sim

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12
Q

as FQ + wavelength _

A

-

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13
Q

as wavelength + FQ_

A

-

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14
Q

the principal interaction in xray production

A

bREMSTRAHLUNG

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15
Q

The ideal material for a target of an xray tube is what?

A

something with high atomic #

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16
Q

mA vs Kvp

A

mA is th tube current

Kvp is th e tube voltage

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17
Q

predominant interaction in the therapeutic range, is this good or bad?

A

predominant interaction is compton scattering, this is bad because scattering is not good

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18
Q

what is the only acceptable interaction to create images

A

photoelectric effect

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19
Q

an incident photon penetrates deep into the atom and ejects an inner shell electron. This process is known as…?

A

photoelectric effect

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20
Q

an xray photon interacts with an outer shell orbital electron. This process is known as….?

A

compton scattering

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21
Q

there is a change in photon direction but does not eject an electron. this is known as?

A

unmodified/ thompsons/ cohernt scattering

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22
Q

photoelectric effect is dependant on what

A

higher z material, the higher the z the more likely it is to be absorbed by photoelectric effect

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23
Q

the relationship between distance and density

A

ISL

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24
Q

What does density in imaging refer to

A

how light or dark an image is

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25
Q

the higher the mA the ____ the density

A

higher

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26
Q

optimal contrast depnds on whay?

A

Kvp

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27
Q

computed radiography uses ______ to convert xrays to digital images

A

photostimable plates

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28
Q

primary method of - scatter

A

colimating the beam

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29
Q

who would cause more scatter, small pts or larger patients

A

large patients

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30
Q

what area would cause more scatter: abdomen or pelvis?

A

pelvis as there is more bone in the pelvis (bone causes more scatter, high Z) abdomen has more soft tissue therefore less scatter

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31
Q

predominant interaction in imaging? kv imaging?

A

kv- photoelectric effect

mv-compton scatter

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32
Q

which has lower dose to pt? Kv or Mv?

A

Kv is 100 X less dose than Mv

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33
Q

T1 vs T2 on MRI

A

T1- longitudinal relaxation time

t2-Transverse relaxation time

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34
Q

MRI uses_____`

A

pulse sequences

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35
Q

FDG is a _____EMITTER

A

POSITON

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36
Q

What is used to create US waves

A

piezoelectrical crystal

37
Q

how many detectors are /cm and per degree

A

1-8 detectors/ cm or 1-5 detecros / degree

38
Q

what do solid state detectors do?

A

convert radiation to light

39
Q

what is pitch

A

the distance that the couch travels through the xray rotation

40
Q

a higher pitch can cause what?

A

+ artifacts

41
Q

whats foltered back projection

A

an algoritihm used to reconstruct CT image aka convolution method

42
Q

what image reconstruction is mostly used now

A

IR iterative reconstruction

43
Q

what is the pros of IR over FBP

A

FBP can have significant artifacts and noise, IR corrects for this

44
Q

CT +1000 is….

A

dense bone

45
Q

CT # 0 is…..

A

water

46
Q

CT # -1000 is….

A

air

47
Q

what is the typical matrix size in CT scan?

A

512 x 512

48
Q

voxel is determined by what 3 things?

A

slice thickness, matrix size and FOV

49
Q

PIXEL VS VOXEL

A

picture element vs volume elemnt

n.b. the pixel is 2 d and vixel is 3d

50
Q

what is isotropic display

A

this is when all planes of the voxel are = ( therefore equal width, length and depth)

51
Q

if after imaging you would like to see improved contrast of the image what would you adjust?

A

window width

52
Q

if i want to view the lung better what would I adjust?

A

the window width, in lung the WW # is typically 500

53
Q

what is tthe effect of a wide WW

A
  • contrast
54
Q

what is the effect of a narrow WW

A

+conrast

55
Q

if I want to - noise of the image what should i do to the mA? kVp?

A

+ kVP and - mA

56
Q

to improve tube longevity what kind of mA should you use

A

LOW if pissible

57
Q

a ring artifact is an indication of what

A

detector malfunction

58
Q

a star artifact is an indication of what

A

metal in the field

59
Q

what causes partial volume artifacts

A

when thick slices are taken

60
Q

what can be used to - motion artifacts

A

using fast scanners

61
Q 
a multislice CT systen uses what?
A: multiple detector beams
b: multi slice beams
c: multiple detctor rows
d: multi-slice rows
e: multiple corn rows
A

E LOL

C is correct answer

62
Q

what is the pro of placing pt prone in pelvis tx

A

it - sm bowel in the field threfore - SE

63
Q

What is diazorate melgulieum

A

this is an oral contrast agent that is aqueous

64
Q

when is aqueous oral contrast used

A

for patients at risk of GI prforation (ex: UC, diverticulitis) where its dangerous for them to have barium sulfate

65
Q

contraindications to IV contrast

A

pt >50
pt with diabetes
pts with impaired kidney fn or cardiovascular disease
or a reaction to contrast in the past

66
Q

what needs to be done before IV contrast

A

bloodwork that looks at EGFR (estimated glomoular filtration rate) ad creatinie levels

67
Q

what EGFR rate is PROBLEM, what happens in this case?

A

EGFR <60

in this instance the patient will have areduced amount of contrast or will not have contrast at all

68
Q

IV contrast 2 types

A

inonic iodine and nonionic contrast

69
Q

ionic iodine has ____ osmoality

A

high

70
Q

what is osmoality

A

particles in solution / kg of water

71
Q

what can high osmoality contrast cause

A

decreased blood pressure

72
Q

what happens in dehydrated pts if they receive high osmoality contrast, what are these patients given?>

A

can cause pt to go into shock

these pts are given low osmoality contrast ex nonionic contrast instead

73
Q

what steps do you take when pt has mild reaction to contrast media

A
  • the injection continues
  • reassure the pt
  • monitor the pt to ensure rection does NOT progress
  • ensure the reaction subsides
74
Q

what steps do you take when pt has intermediate reaction to contrast media

A

stop the injection- pt requires careful observation to ensure a severe rection does not occur

75
Q

what steps do you take when pt has severe reaction to contrast media

A

stop injection, prompt medical attention is required, pt is often hospitalized

76
Q

when do most reactions occur from contrast media

A

70% occur within first 5 mins the rest occurs within half an hour

77
Q

what subsites need to fast prior to SIM

A

H&N, lung, brain and PROS

78
Q

when is contrast admin in H&N and lung

A

seconds before the scan via power injector

79
Q

when is contrast admin for brain

A

10-30 mins before CT via IV push

80
Q

when to admin contrast for liver

A

20-40 seconds before scan to visualise hepatic artery, 60-90s to view portal vein

81
Q

when to admin contrast for pelvis

A

not all pros patients get contrast- if administered:
15 mins before CT IV injection
Barium can b given orally 30-60 mins before scan to visualize sm bowel

82
Q

when to admin contrast for GI

A

Oral contrast is used:

baroum is taken orally 30-60 mins before scan

83
Q

what sites get IV contrast

A

lung, H&N, brain, liver, sometimes PROS

84
Q

contrast media needs _____ in order to -______

A

needs to have low atomic # to - artifacts

85
Q

when the scanner is triggered to aquire images/ treat during a certain part of respiration, this is called _____

A

prospective axial scanning

86
Q

with PET scanning _____ is used to create the image
A: KV XRAYS
B: 511 kev gamma rays that move in almost opposite directions
C: 6MV gamma rays
D: Magnetic pulses

A

B

87
Q

mA is the ____ of the beamand controls ______.

kVp is the ______ of the beam and controls ______.

A

mA is the quantity of th beam and controls density

kVp is the quality of the beam and controls contrast

88
Q

VMAT is best used for what type iof tumours ?

A

central, well defined tumours

Ex: central lung cancer or prostate

Skin Radiation therapy (40 decks)

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