Mammography Flashcards
(63 cards)
1
Q
mammography equipment
A
- angled tube head
- c-arm design
- fixed focus-detector distance
- compression device
- fixed field size
- grids
- AEC
2
Q
difference between conventional and mammography x-ray HOUSING tubes
A
conventional: glass envelope
mammo: metal tube
3
Q
difference between conventional and mammography x-ray ANODE
A
conventional: tungsten
mammo: grounded Mo, Rh anode
4
Q
difference between conventional and mammography x-ray axis of rotation
A
C: horizontal
M: vertical
5
Q
difference between conventional and mammography x-ray filters
A
C: Al filter dose reduction
M: Mo or Rh filters for spectral shaping
6
Q
difference between conventional and mammography x-ray anode angle
A
C: 7-16deg
M: 0deg; tube tilt 26deg
7
Q
mammography x-ray tube operating voltage
A
23-40kVp
8
Q
dual filaments in a focusing cup
A
0.3mm (contact) and 0.1mm (magnification) focal spot size
9
Q
why use small focal spot
A
- minimize geometric blurring
- maintains spatial resolution
10
Q
typical tube currents
A
100mA +/- 25mA for large focal spot
25mA +/- 10mA for small focal spot
11
Q
what track is used for anode
A
Mo/Rh targets, sometimes combination with Tungsten
12
Q
reason for choosing Mo and Rh as anode targets
A
charateristics xray production
Mo - 17.5 and 19.6 keV
Rh - 20.2 and 22.7 keV
13
Q
why is tube tilted by 26deg
A
minimize effective focal spot size
14
Q
what are the 3 factors that xray beam spectrum depend on
A
- anode material
- selected filter
- kV
15
Q
why is low kVp used
A
- minimise compton scattering and maximise photoelectric effect -> enhance differential absorption by various tissues of the breast
- reduce radiation dose to breast -> glandular tissue of breast is high radiosensitive
16
Q
use of a filter of ____ element as x-ray tube target is designed to
A
same; suppress the lower and higher energy bremsstrahlung x-ray and allow transmission of characteristics x-ray energy
17
Q
what does the lower and higher energy bremsstrahlung xray contribute to
A
lower - radiation dose
higher - loss of contrast
18
Q
xray tube window is made of
A
Berylium
19
Q
breast thickness and its recommended target, filter and kVp
A
fatty breast ~4cm thick:
- Mo target
- 30micron Mo filter
- 24-26kVp
glandular breast ~5-7cm thick:
- Mo target
- 25micron Rh filter
- 27-31kVp
> 7cm:
- Rh target
- 25micron Rh filter
- 27-31kVp
20
Q
what does HVL depend on
A
- kvp
- compression paddle thickness
- added tube filtration
- target material
- age of tube
21
Q
relationship between kvp, HVL, atomic number targets and filters
A
HVL increases with higher KVP and higher atomic number targets and filters
22
Q
AEC modes of operation
A
- auto time
- auto kvp
- full automatic
23
Q
why is there a need for breast compression
A
- reduces overlapping anatomy and decreases tissue thickness
- less scatter, more contrast, less geometric blurring of the anatomic structures, less motion and lower radiation dose to the tissues
- better visualisation of tissues near the chest wall
24
Q
what is spot compression
A
- apply compression to a smaller area of tissue using a small compression plate or cone
25
what does scatter radiation do to the images
degrades subject contrast and detail
26
relationship between scatter, breast thickness and area
scatter increases with breast thickness and breast area
27
main variables of a mammo imaging system
- contrast
- sharpness
- dose
- noise
28
why and how is half field xray beam used in mammo
- angled such that the central ray comes down along the chest wall edge perpendicular to the detector
- eliminated unnecessary dose to the patient's torso
- prevents non-visualisaion of tissue in the chest wall region
29
explain the anode heel effect
- lower xray intensity is on the anode side of the field and should be placed at where nipple edge is.
- more tissue at chest wall, so require more intense xray beam
- a more uniform exposure is achieved
30
what is the optimal viewing conditions of a mammo image
soft copy:
- ambient light intensity <20lux
- display monitor 5MP
- magnifiers available to view fine deatils such as microcalcifications
hard copy:
- films are exposed to high optical densities to achieve high contrast
- luminance of mammo viewbox should be at least 3000cd/m^2
- film masking - preserve visibility of low contrast details
31
advantages of analog mammo over DM
- more affordable
- superior spatial resolution
- can be transformed into digital images with CR and saved as DICOM
- no digital detector -> which is a fragile and expensive part
- easier to maintain
32
disadvantage of analog mammo over DM
- uses film so need a CR reader to convert image to digital --> takes a longer time to receive the image
- 2 systems working together (machine and CR reader, if one breaks, the entire process is down
- difficult to archive images unless have CR
33
advantages of DM over analog in terms of lower patient dose and reduced recalls
- lower dose
- wider dynamic range
- higher contrast resolution
- better SNR
- reduced false positive and increased PPV
- image manipulation tools
34
advantages of DM over analog in terms of improved efficiency
- simplifies storage and retrieval of images
- elimination of lost films
- images can be easily transferred electronically to a central location (PACS) for diagnosis
- availability of CAD
35
advantages of DM over analog in terms of enhanced patient care and productivity
- elimination of need to leave exam room to process films
- eliminates processing issues
- faster interventional procedures
- faster patient throughput
36
disadvantage of DM over analog
- more expensive
- delicate digital detector
- more sensitive to ambient temp
- spatial resolution is limited to pixel size
- harder to service
37
does digital or film screen have a better contrast resolution
digital - wider latitude = greater dynamic range = more shades of grey
38
what target material is used for digital mammo
- tungsten (W) is better as the kV is more for penetration since the algorithm drives contrast
- W offers lower dose with longer scale contraste
39
what filtration is used for digital mammo
Rh and Ag
40
what are the 2 types of digital mammo
direct and indirect
direct: convert xray directly to electronic signals
indirect: convert xray -> light -> electronic signals
41
what are some image quality measurements
- modulation transfer function (MTF)
- detector quantum efficiency (DQE)
42
explain MTF
- measure of signal transfer over a range of spatial frequencies -> image sharpness
- high MTF = more transfer = sharper image and superior contrast
43
explain DQE
- measure of dose efficiency
- high DQE = superior image quality and reduced patient dose
- high DQE = lower image in noise = reduced missed cancers
- high DQE = flexibility to reduce dose
44
what is the preferred target filtration combination of a full field digital mammo
W/Rh
45
what is tomosynthesis
- set of rapidly acquired low-dose projections taken at multiple angles through the compressed breast
- then used computer reconstructions to create 3D images of the breast
46
compare narrow and wider sweeping angle for tomosynthesis
- wider sweep angle = gives more complete blurring outside of the focal plane
- narrow sweep angle = lesion margins appear sharper
47
advantages of DBT compared to 2D
- better depiction of the smallest calcifications
- better delineation of the lesion border
- less compression
48
disadvantage of DBT compared to 2D
- motion artifacts more likely to occur because of longer exposure time
- large calcifications cause significant artifacts
- reconstructed images lengthens interpretation time
49
how is breast dose calculated
mean glandular dose (MGD) - measured in mGy or mrad
MGD (mrad) = DgN x ESE
50
what is the acceptable dose
for a 50-50 glandular adipose tissue breast, with 4.2cm compression thickness, MGD must be less than 3mGy per view
51
factors affecting breast dose
- photon energy
- breast composition and thickness
- equipment
52
what is DgN
factor that converts ESE to mean dose
depends on:
- HVL, filter, target, kVp
- breast composition and thickness
53
what are some patient related artefacts
- motion
- skin line
- hair
- anti-perspiration
- superimposition of body parts
- eye glasses
- jewelry
54
what are some hardware-related artefacts
- dust/cracks on compression paddle
- under exposure
- field inhomogeneity
- collimation misalignment
- noise obscuring calcification
- grid lines
- grid misplacement
- vibration artifact
- detector-associated:
ghosting
gouging
horizontal line artifact
dead pixel
unread lines
55
what are some software processing artefacts
- high density
- loss of edge
- breast within breast
- vertical processing bars
- detector interface line
- skin line processing
56
what is a storage related artefact
reconstruction artifact
57
why is laser printer sensitometry QC performed
- ensure that the film sensitometry is operating within tolerance level
58
why is SMPTE QC performed
- to determine whether the contrast and brightness setting of the monitors are acceptable
- to check for limitations in spatial resolution and aliasing of displays
- to check for non-uniformities, scratches and other defects
59
what is ACR phantom used for
- to assess the quality and consistency of the mammographic images
60
what do SNR and CNR measure
- both are a measurement of image quality
SNR: ratio of a signal power to the noise power corrupting the signal
CNR: ability of an imaging modality to distinguish between various structures of an acquired image by the perception of differences in their apparent signal intensities
61
what is a compression thickness indicator QC for
to ensure that the indicated compression thickness is within tolerance
62
what is the flat field uniformity test
- an analysis of the homogeneity of detector field
- to ensure that the images are uniform in intensity and free of artifacts
63
what is gain and geometry calibration for
to ensure that the system is calibrated properly
