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Specialized Gen Rad > Week 10 > Flashcards

Week 10 Flashcards

1
Q

Gold standard for detecting breast lesions

A

Mammography

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2
Q

purpose of angled tube head

A

to counter anode heel effect as cathode aligned over chest wall & anode over nipple

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3
Q

purpose of C-arm setup

A

gantry rotation

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4
Q

what is the FDD

A

65-66 cm

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5
Q

why is FDD fixed

A

fixed to balance low patient dose while ensuring high film dose; higher FDD = longer exposure & motion unsharpness, lower FDD = high patient dose

only one type of exam done

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6
Q

compression force used

A

100 – 150 N (never greater than 200N)

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7
Q

importance of compression

A
  • reducing overlapping anatomy and tissue thickness
  • less scatter, geometric blurring, motion, and dose
  • increasing contrast and visualisation of tissues
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8
Q

what do screen film mammo use for AEC

A

photo timers instead behind cassette to prevent over/under exposure

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9
Q

what does the phototimer use

A
  • radiation sensor
  • amplifier
  • voltage comparator
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10
Q

what happens if there is insufficient dose to trigger comparator switch

A

backup timer terminates exposure; Retake requires higher energy beam to be selected for greater beam penetration

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11
Q

digital mammo AEC

A

Voltage and current adjusted based on thickness and composition of breasts

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12
Q

AEC modes of operation

A

auto time, auto kVp, full automatic

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13
Q

auto time

A

kVp, target/filter chosen by operator

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14
Q

auto kVp

A

kVp based on breast thickness

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15
Q

full automatic

A

kVp, target/filter chosen by unit

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16
Q

anode design for mammo

A

rotating anode

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17
Q

what does SFM use for anode

A

dual track Mo/Rh, sometimes with tungsten

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18
Q

why is Mo/Rh mainly used

A

their characteristics x-ray production near optimum energy for mammo

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19
Q

common dual tracks

A

Mo/Rh & Mo/W

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20
Q

benefit of dual track anode

A

More anode material choices

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21
Q

limits of dual track anode

A
  • less reliable
  • more expensive
  • lower maximum anode heat loading than single tracks
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22
Q

what does DM use for anode

A

single track Tungsten

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23
Q

when is Mo used for DM

A

small to avg breast thickness

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24
Q

when is RH & W used for DM

A

larger breast thickness

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25
Q

benefit of single track

A

Can deliver high current exposure (2-3x compared to dual track) needed for thicker breasts at appropriate exposure time = reduce motion artifacts

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26
Q

what filters do DM use

A

W/Rh & W/Al filters

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27
Q

what is the voltage used for mammo

A

22 - 40 kVp

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28
Q

what is the filament used for mammo

A

Dual filaments in focusing cup (0.3 mm for contact, 0.1 mm for magnification)

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29
Q

what is the FSS used for mammo

A

Small FSS to minimize geometric blurring & spatial resolution

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30
Q

what is tube current used for mammo

A

o 100 mA +/- 25 mA for large 0.3 mm FSS
o 25 mA +/- 10 mA for small 0.1 mm FSS

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31
Q

purpose of anode angulation

A

changing FSS; tilting used to reduce FSS and mitigate anode heel effect

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32
Q

mammo vs conventional = housing

A

mammo = metal tube
conventional = glass envelope

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33
Q

mammo vs conventional = anode material

A

mammo = Grounded Mo, Rh anode
conventional = Tungsten anode

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34
Q

mammo vs conventional = anode angle

A

mammo = 0 degrees but tube tilted 24 degrees [minimizes effective FSS]
conventional = 7 – 16 degrees

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35
Q

mammo vs conventional = axis of rotation

A

mammo = Vertical
conventional = Horizontal

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36
Q

mammo vs conventional = filter & function

A

mammo = Mo/Rh for spectral shaping
conventional = Aluminium for dose reduction

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37
Q

what is needed for high contrast sensitivity

A

low photon energy

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38
Q

ideal spectrum for mammo

A

photons of same energy (mono energetic x-rays of 15 – 25 keV) with adjustable energy for different breast conditions

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39
Q

ideal spectrum for mammo achieved via

A
  • target material
  • selected filter
  • kVp range
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40
Q

how does selected filter achieve ideal spectrum for mammo

A

Helps remove unnecessary high & low energy bremsstrahlung x-rays to allow transmission of characteristic x-rays and lower patient dose

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41
Q

why is Beryllium used for x-ray tube window

A

allows transmission of lower energy photons and minimizes radiation absorption in tube

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42
Q

how does low kVp achieve ideal spectrum for mammo

A

minimize Compton scattering [reduce dose to breast as glandular tissue is radiosensitive]

maximize photoelectric effect for better differential absorption of various tissues in breast

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43
Q

HVL factors

A
  • kVp,
  • compression paddle thickness,
  • added tube filtration,
  • target material
  • tube age
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44
Q

HVL increases with __ kVp and __ atomic number targets and filters

A

higher; higher

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45
Q

HVL dependent on what in breast tissue

A

strongly dependent on tissue composition (glandular, fibrous, adipose)

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46
Q

how diff is mammo x-ray generator to conventional x-ray generator

A

 Generating power rating is 3 kW
 Voltage (22 – 40 kVp)
 AEC circuit different
 High frequency generators at 6 KHz

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47
Q

where does scatter radiation plateau at

A

between 25 – 35 kVp

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47
Q

why is scatter radiation bad

A

Degrades contrast and detail which increases with increased thickness & area of breasts but constant between 25 – 35 kVp

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48
Q

Without scatter rejection, only___ of subject contrast detected

A

50 – 70%

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49
Q

why is stationary grid not used

A

compromise image quality as grid may cover tiny details (microcalcifications)

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50
Q

why are oscillating grids used

A

grid lines eliminated by grid motion

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51
Q

Linear grids use __

A

4:1 to 5:1

52
Q

Higher grid ratio removes scatter more but also __

A

increases dose to breast

53
Q

Interspace materials

A

Carbon fiber or organic fiber

54
Q

why is carbon fiber > organic fiber

A

Carbon fiber better as aluminium attenuates too many low energy x-rays

55
Q

Grid frequency / lead strip densities for moving & stationary grids

A

 30 – 50 lines / cm for moving
 Up to 80 lines / cm for stationary

56
Q

mammogram variables

A

contrast, sharpness, dose and noise

57
Q

importance of spatial resolution

A

to see microcalcifications

58
Q

how is spatial resolution achieved

A

o Pixel size / film screen combo
o FSS
o Compression
o Anti-scatter grid

59
Q

How different is x-ray beam for mammo different from conventional means

A

Half of potential beam collimated out & angled till CR perpendicular to chest wall edge perpendicular to detector

Done to eliminate dose to torso and prevents non visualization of tissue in chest wall

60
Q

viewing conditions for mammo vs conventional

A

mammo uses
- 5 MP compared to regular 3MP
- Magnifiers used
- Ambient light intensity < 20 lux
- Hard copies 3000 cd/m^2 compared to 1500 cd/m^2
- Film masking used to visualize low

61
Q

pros of analog mammography

A
  • More affordable
  • Better spatial resolution
  • Can be transformed into digital images using CR and saved as DICOM
  • No digital detector / cheaper repairs
  • Easier to maintain
62
Q

cons of analog mammography

A
  • Uses film hence needs CR reader to convert image into digital one then receive image
  • 2 systems required to work; if 1 breaks down, entire process broken down
  • Difficult to archive unless have CR
63
Q

goals of digital mammography

A
  • Lower dose and reduced recalss
  • Enhanced patient care
  • Improved efficiency
64
Q

disadvantages of digital mammography

A
  • More expensive, fragile, sensitive to ambient temperature
  • Spatial resolution limited by pixel size but can visualize small high contrast structures
  • Harder to service & maintain
65
Q

DM vs SFM for sensitivity & specificity

A

DM was more sensitive than SFM but specificity is similar

66
Q

what is Mo ideal for in digital mammography

A

SFM ranges & gray scale

67
Q

what is W ideal for in digital mammography

A

kV is more penetrative since algorithm drives contrast & lowers dose with longer scale contrast

68
Q

what is Ag filter ideal for in digital mammography

A

larger denser breasts but same quality as Mo x-ray

69
Q

digital mammography capture types

A

o Direct = xray > electronic signals
o indirect = xray > visible light > electronic signals

70
Q

what is used for small field system biopsies

A

CCD

71
Q

what does indirect digital mammo use

A

amorphous silicon

72
Q

what does direct digital mammo use

A

amorphous selenium

73
Q

MTF

A

modulation transfer function

74
Q

what is MTF

A

measure of signal transfer over range of spatial frequencies for image sharpness

75
Q

higher MTF =

A

sharper images, superior contrast resolution, sharper microcalcifications

76
Q

DQE

A

Detector Quantum Efficiency (DQE)

77
Q

what does DQE measure

A

dose efficiency

78
Q

higher DQE =

A

superior image quality via reduced dose & noise

79
Q

digital breast tomosynthesis narrow sweep best used for

A

better in-plane resolution & microcalcification visualization

80
Q

digital breast tomosynthesis wider sweep best used for

A

better out-of-plane resolution & visualization of larger objects that occupy multiple planes such as masses & architecture distortion

81
Q

pros of digital breast tomosynthesis

A

o Better visualization of microcalcifications
o Better delineation of lesion border
o Less compression

82
Q

cons of digital breast tomosynthesis

A

o Motion artifacts due to longer exposure time
o Large calcifications cause significant artifacts
o Longer time needed for reconstruction & interpretation by radiologist

83
Q

MGD

A

Average/Mean glandular dose

84
Q

what is MGD related to

A

more radiosensitive tissues prone to radiation induced carcinogenesis

85
Q

what is the limit of MGD

A

Limited to 3 mGy / 300 mrad per view for compressed breast thickness of 4.2 cm with breast composition of 50% glandular and 50% adipose

86
Q

what happens if MGD > 3 mGy

A

cannot proceed with mammogram

87
Q

MGD formula

A

MGD = DgN x ESE (R) (Entrance Skin Exposure)

88
Q

what is DgN

A

normalized glandular dose

89
Q

DgN factors

A
  • HVL, kVp, target, filter
  • Breast composition & thickness
90
Q

dosimetry factors

A
  1. photon energy
  2. breast compression & thickness
  3. equipment
91
Q

how does photon energy affect dosimetry

A

higher kVp = higher beam penetration (lower ESE & MGD) = lower subject contrast

92
Q

how does breast compression & thickness affect dosimetry

A

glandular tissue have higher breast dose due to higher attenuation and more fat mass at risk

93
Q

how does equipment affect dosimetry

A

 Rh/Rh combo results in lowest avg dose followed by Mo/Rh then Mo/Mo
 Screen film speed & processing conditions influence IR sensitivity
 Higher OD target on film increases dose
 Grid use increases dose

94
Q

what does mammo qc assess

A
  • Noise,
  • contrast,
  • spatial resolution
  • Dose
  • Artifacts
95
Q

what should u use to wipe monitors

A

using water / approved monitor face cleaner; don’t use alcohol or abrasive materials

96
Q

what does Society of Motion Picture & Television Engineers determine

A
  • Determines whether contrast & brightness are acceptable
  • Checks for spatial resolution & aliasing of displays as well as non-uniformities, scratches and other defects
97
Q

SNR

A

quantitative description of info quality carried by image

98
Q

CNR

A

ability to distinguish diff structures on acquired image

99
Q

what anode does SFM use

A

dual track Mo/Rh sometimes with W

100
Q

what anode does DM use

A

single track W due to performance advantages

101
Q

how does dust appear on compression paddle

A

appears on different views at different regions of breast but consistently at same place

102
Q

how does underexposure appear on image

A

grainy image like salt & pepper

103
Q

what are the causes of underexposure

A
  1. exposure prematurely terminated
  2. photocell close to edge of breast
104
Q

what are the causes of field in-homogeniety

A

Phantom used was not at optimum temperature prior to exposure

105
Q

how does collimator misalignment appear on image

A

Vertical white line along chest wall edge of image

106
Q

how does noise obscuring calcification appear on image

A

grainy texture due to underexposure

107
Q

how to rectify noise obscuring calcification artifact

A

Higher exposure compensation by ~30% to lower noise & improve contrast

108
Q

how does grid misplacement appear on image

A

Not fully engaged with clearly demarked line shown

109
Q

how does vibration artifact appear on image

A

black & white lines seen

110
Q

how does ghosting appear on image

A

double images; needs to have complete erasure prior to use

111
Q

how does gouging appear on image

A

multiple circular artifacts due to repeated hitting of compression paddle on unprotected IR

112
Q

how does dead pixels appear on image

A

black and white like grainy appearance

113
Q

how does high density artifact appear on image

A

salt and pepper grainy appearance

114
Q

how does loss of edge appear on image

A

incomplete jagged appearance due to large breasts or implants

115
Q

how does breast within breast appear on image

A

2 breasts inside each other

116
Q

how does detector interface line appear on image

A

2 halves of detector clearly drawn

117
Q

how does skin line processing appear on image

A

black surrounding line around breast

118
Q

causes of reconstruction artifact

A

 Incorrect storage of frequency coefficients for image
 Cannot recover image from PACS

119
Q

causes of detector interface line artifact

A

Difference in calibration of 2 halves of detector and high exposure for imaging very dense breast

120
Q

causes of vertical processing bar artifact

A

 Diff in pre-amplification gains among diff pixel blocks in detector
 Diff are usually small and normalized to each other for uniform image

121
Q

causes of breast within breast artifact

A

Rapid changes in breast thickness or tissue densities separating central & peripheral regions causes software to create falsely exaggerated boundary

122
Q

causes of high density artifact

A

Detector elements below receive significantly less exposure and hence weak signal

123
Q

causes of unread line artifact

A

 Line not read out on detector due to software issue
 New detector readout sequence file needed

124
Q

causes of horizontal line artifact

A

Defective pixel line / incorrect readout

125
Q

causes of grid line artifact

A
  • Failure of motor during imaging
  • Stopping / slowing down of grid oscillation [grid speed cannot be changed by rad tech]
126
Q

what artifacts give grainy appearance

A
  • high density artifact,
  • noise obscuring calcification,
  • dead pixels,
  • underexposure
127
Q

what artifacts give line appearance

A
  • grid lines,
  • detector interface line,
  • vibration artifact,
  • vertical processing bar,
  • horizontal line,
  • unread line,
128
Q

what is the same as 0 degrees anode angle & 24 degrees tube tilt

A

16 degrees anode angle & 6 degrees tube tilt

Specialized Gen Rad (13 decks)

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