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RAD413 > Mammography Physics > Flashcards

Mammography Physics Flashcards

1
Q

Be aware that fibrous tissue and cancer have similar attenuation coefficients

A
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2
Q

What is the difference between breast tissue composition in older and younger breasts

A

Larger/older breast = higher fat content

Younger breast = tends to be fibro glandular

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3
Q

How does high glandularity of breast tissue affect the sensitivity and specificity

A

High glandularity limits the sensitivity and specificity of

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4
Q

What is high glandularity

A

Lots of fibrous tissue

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5
Q

What does sensitivity and specificity mean in terms of breast tissue

A

Sensitivity - ability to identify cancer

Specificity - ability to identify normal/benign properties

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6
Q

What are the 3 types of tissue found in the breast

A

Glandular
Fibrous
Adipose tissue

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7
Q

Compare the variation of attenuation coefficient with kV of carcinoma, fibrous tissue, fatty tissue

A

Carcinoma has the highest linear attenuation coefficient at a certain photon energy, then fibrous tissue then fatty tissue at the same photon energy

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8
Q

What type of energy is needed for mammography and why

A

Low energies are required to provide adequate contrast in image

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9
Q

Where would the automatic exposure chamber be found on the mammography machine

A

Positioned in area of typical high density breast tissue

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10
Q

What effect does mammography utilise

A

Anode-heel effect

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11
Q

What are the 3 different filter materials used in mammography

A

Molybdenum (k-edge 20kev)

Rhodium (k-edge 23kev)

Tungsten (W) (k-edge 69kev)

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12
Q

What material is the window of the mammography made of

A

Beryllium

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13
Q

Know that mammography uses shorter SID than xray

A
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14
Q

What is the size of the fine focal spot of mammography

A

0.1-0.3mm

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15
Q

Find a diagram of a mammography and label the different parts

  • angulation indicator scale
  • tube head
  • face guard
  • compression device
  • cassette holder
  • AEC chamber
  • automatic release foot pedal
  • up and down movement controls
A
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16
Q

Describe what the anode heel effect is

A
  • anode is angled
  • photons that hit the anode end have further to travel to exit anode hence form lower energy X-rays
  • photons at anode angle/cathode end have less material to travel through to exit anode hence form higher energy xrays
  • overall this forms a spectrum of xray energies increasing in energy as it travels up the angle of the anode
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17
Q

Explain how the attenuation of xrays work in mammography / how patient absorbs dose

A
  • xray bream travels through tissue, low energy xray give their energy more easily than high energy xray
  • absorption of energy of xray gives the dose to the patient
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18
Q

Why is the patient dose in mammography greater than regular xray

A

Low energy xrays need to be used for better contrast hence more xrays are required to get the image which increase dose

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19
Q

What concept/ principle brings about image formation in mammography

A

Different tissues attenuate xrays by different amounts providing our image

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20
Q

Be aware that at low energies, the difference between tissues is greater. So low energies give more contrast.

Hence, you must balance between dose and contrast

A
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21
Q

What is the purpose of anode rotation in mammography

A

Heat dissipation

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22
Q

Know that in mammography we can have filter combination/targets, give an example

A

Molybdenum and rhodium

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23
Q

What is the purpose of filter combination in mammography

A

for the spectral shaping of the beam for a given target (anode), which affects image contrast and radiation dose

  • e.g W/Rh combination filter is used to produce higher energy xray beam
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24
Q

What is k-edge

A

the abrupt increase in the photoelectric absorption of x-ray photons observed at an energy level just beyond the binding energy of the k-shell electrons of the absorbing atom.

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25
Q

What 4 things are factors contributing to image quality in mammography

A
  • contrast
  • resolution/blur
  • noise
  • dose
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26
Q

What are some things that affect contrast in terms of imaging quality

A
  • energy
  • target/filter combination
  • scatter
  • windowing/levelling
  • digital post processing
  • display monitors
  • ambient viewing conditions
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27
Q

How is scatter reduced in 2 ways in mammography

A

Grid
Compression

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28
Q

What are 3 types of scatter and how does scatter affect image quality

A
  • unchanged
  • absorbed
  • scattered
  • reduced contrast
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29
Q

What 6 things can affect image quality resolution

A
  • focal spot size
  • magnification
  • compression
  • movement
  • digital processing
  • pixel pitch
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30
Q

How does focal spot size affect image quality

A

Large focal spot causes blurred image due to penumbra

Hence small focal spot used in mammography

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31
Q

Why is an even smaller focal spot needed if there is magnification

A

Magnification creates larger image of small details, hence you need an even smaller focal spot as blurring increased

32
Q

What is the typical thickness of a compressor breast

A

2-11 cm

33
Q

What are 2 main types of abnormalities that can be found in the breast

A
  • low/high contrast masses
  • calcification
34
Q

What equation calculates the force applied to breast

A

F = ma

35
Q

How does compression of breast support mammography in terms of dose and contrast

A

As compression give lower breast thickness, you don’t need as penetrating a beam.

  • can reduce energy of beam meaning contrast increases
36
Q

What 3 benefits does compression of breast provide

A
  • reduces breast thickness variation
  • reduces latitude required
  • reduces variation in optical density (OD) across image
37
Q

What are the 5 ways breast compression can improve image quality or patient dose

A
  • reduced dose
  • improved contrast ( less scatter, softer spectrum)
  • improved resolution/blurring
  • reduced range of tissue attenuation
  • improved visualisation (less overlap of structures)
38
Q

What are 2 main ways of reducing movement blur

A
  • minimise exposure time
  • compression
39
Q

What are the 4 areas/measurement of quality control as part of the quality assurance program

A
  • dosimetry
  • image quality tests
  • equipment movement
  • safety features
40
Q

What does DID stand for in mammography

A

Digital image display

41
Q

What is threshold contrast detection

A

a commonly used tool to assess image quality of imaging systems.

Find image and know what it looks like

42
Q

What is digital breast tomosynthesis

A
  • series of 2D images created in planes angled to the detector
  • reconstructed tomohynthesis planes can be synthesised into a 2D image
43
Q

What is the angular range of digital breast tomosynthesis

A

Varying angular range up to 50 degrees

44
Q

Why does DBT have improved sensitivity and speciality compare my to regular mammography

A

Removes overlapping tissues in the reconstructed planes

45
Q

What is digital breast tomosynthesis particularly useful for scanning

A

Useful for imaging dense tissue

46
Q

DBT is not used in routine screening only assessment

A
47
Q

What is the difference between step and shoot and continuous shooting in digital breast tomosynthesis

A

A CSSM acquisition provides more counts than the corresponding SSM due to extra data collected as the detector moved from one view to the next

48
Q

Be aware that DBT issues anti scatter grid and regular does not

A
49
Q

What 4 things can be measured to analyse image quality in DBT

A
  • geometric distortion
  • artefact spread
  • CNR
  • MGD
50
Q

What is geometric distortion

A

unwanted “warping” of the image that distorts the spatial relationship among objects in the image

51
Q

What is artefact spread

A

when there is an area with an assemblage or numerous artifacts spread on the surface

52
Q

What is MGD

A

Mean glandular dose

  • the average radiation absorbed dose to the breast glandular tissue in mammography examinations.
53
Q

What are 6 issues/disadvantages associated with digital breast tomosynthesis

A
  • longer exposure time
  • larger datasets
  • increase QC workload
  • additional dose
  • artefacts
  • additional reporting time
54
Q

What is contrast enhanced mammography

A
  • using iodine contrast agent
  • low and high energy images in succession
55
Q

What is contrast enhances mammography image formed

A
  • post processing creates image showing iodine accumulation and removes breast structure
56
Q

Why is iodine used as contrast in contrast enhances mammography

A
  • iodine accumulation seen on scan is a potential indicator of cancer
57
Q

What is the relation of contrast to noise ratio and iodine concentration

A
  • CNR increases linearly with iodine concentration
58
Q

What is the mean glandular dose

A

Dosimetry model for a standard breast

59
Q

The standard percentage of glandular tissue in the central region of breast is ?

A

29%

60
Q

What is the remedial level of dose value compared to the standard breast

A

2.5mGy

61
Q

What is the correlation between mean glandular dose and breast thickness

A

Increase in breast thickness directly causes Increase in mean glandular dose (mGy)

62
Q

What is NDRL

A
  • national diagnostic reference level
63
Q

What is the purpose of national DRLs for screening mammography

A

Early identification of breast cancer

64
Q

What is dose audit/ its purpose

A

dose audit is to audit the minimum dose needed and make sure it hasn’t increased due to any changes in the manufacturing process.

65
Q

Breast tissue is relatively radio sensitive

A
66
Q

What does SQAS, RQAS, NQAT, PHE stand for

A

Screening quality assurance service
Regional QA centre
National QA team
Public health england

67
Q

Clear establishment of remedial and suspension levels of performance as part of quality assurance

A
68
Q

What is NHSBSP

A

National breast screening program

  • established in 1988 and routinely invites women aged 50-70 for breast screening every 3 years
69
Q

What is the average dose given to patient for scan of 2 breast

A

4mGy

70
Q

What is the assumed mean glandular dose per mammogram

A

1 mGy

71
Q

What are 2 risks not relating to dose with mammography/screenjng

A

Overdiagnosis - detecting cancers that would not have a detrimental effect on life

False positives/negatives

72
Q

3 main areas of artefacts on mammography

A
  • patient related
  • equipment
  • digital post processing
73
Q

Know what an under or over exposed breast looks like on mammogram

A
74
Q

What are 3 specific artefacts that can be seen on mammogram image + describe what they are

A
  • grid lines (grid lines superimposed on image)
  • anti perspirant artefact (faint radiopaque densities in axilla region due to deoderang)
  • image processing artefact (attempts to find edge of breast resulting in loss of edge artefact)
75
Q

Familiarise yourself with what the mammography artefacts look like, grid lines, anti persoirant, loss of edge

A
76
Q

Low kVp permits utilisation of photoelectric absorption and maximises radiographic contrast between fibro glandular tissue and cancer

A
77
Q

Quality assurance is essential to maintaining standards in the breast screening programme, particularly focusing on image quality and dose performance measures

A

RAD413 (24 decks)

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