Mammography Flashcards
What are the types of tissues in the breast and what simularities does it have?
- Adipose
- Glandular
- Fibrous
- Tumours
Simular densities and atomic numbers, but Z# is main factor
With mammography, what energy do you use and what type of the material is the target?
-Use low E
-Use molybdenum target
What type of radiation do we ussually get when in mammography?
-We ussually get charecteristic radiation (because Z# is lower, and kVp is at 30 kVp)
What percentage of the beam is k-charecteristic in mammography?
20-30%
For breast imaging, what is the average energy?
17-24 kEV
What are ways that we can control beam quality in mammography?
- Filtration
- Anode to Cathode distancce
- Equipment composition
What type of filters/target do we use in mammography?
-We would use k-edge filters
-Specifically using a molybdenum filter with a molybdenum target
What benefits do we have in the image when we add filtration?
It narrows the range of energy to increase subject contrast
When is a Rhodium filter used?
When you have a patient with thicker breast tissue
What is the K-edge for Rhodium?
24
What type of radiation would you have when you use a Rhodium filter? What changes would occur?
-You would have mostly Bremms radiation
-An increase in charecteristic radiation
What is the difference in average energy when you use a rhodium filter vs a molybdenum filter?
The average energy is the same, although you would have more Bremms radiation with a rhodeium filter
With a lower kVp, will the space charge be larger or smaller?
The space charge would be larger because youre not pulling e- across as effectively
What are the effects of having a very low kVp regarding space charge?
-Filament gets hotter, so it could cause vaporization
-Attenuation of the beam before hitting the target
Why does mammography have shorter cathode to anode distance?
-Less attenuation of the beam before it hits the target
-Less vaporization
What does the pyrex glass in the tube do regarding attenuation?
Filters out low energy photons
In mammography, what is the window made out of?
Beryllium
What pieces of eqipment are modifed in mammography?
- Window
- Mirror
- Glass tube
- Anode angle
What type of radiation is produced with a molybdenum filter and a molybdenum target? What is the expected keV after filtration?
-All radiation but more charecteristic
-17-19 keV
What type of radiation is made with a molybdenum filter and a tungsten target? What is the expected keV after filtration?
-Bremms
-17-19 keV
What type of radiation is made with a rehnium filter and a molybdenum target? What is the expected keV after filtration?
-Bremms
-20-23
What type of radiaiton is made with a rehnium filter and a rehnium target?
Charecteristic
What type of anode angle does is used in a mamography machine? Why?
-A very small anode ange
-For better spatial resolution
What are the cons of a small anode angle?
-Anode heel effect
-Smaller uniform field size
Why do we use a low output in mammography?
-Because we have a llow mA and a low fluxence, both of these combine for a longer exposure time
What are the pros of having a shorter SID in mammography?
- Increase in mGy/mAs
- Shorter exposure time
What are the cons of having a shorter SID in mammography?
- Higher dose
- Less sharpness
- Greater anode heel effect
How do we compensate for the anode heel affect in mammography?
Tilt the x-ray tube so that the anode is higher than the cathode
What are the pros of having a tube tilt to compensate for the anode heel effect in mammography?
three
- Increase in mAs/mGy
- More uniform beam
- Larger field size
What are the cons of having a tube tilt in mammography?
Why?
Less spatial resolution because the field size is larger and the anode is not as bent
What 2 systems work together so that AEC can function?
- AEC
- Compression device
Where are the AEC detectors located in mammography? Why?
After the IR, because with low energies, we would see the detectors on the image
What selection is made after the AEC is set up in mammography?
Both AEC and compression device combine to select optimal technique and target material
How does the AEC work in mammography?
Sends out a 100ms burst of radiaiton before the exposure to tell how much radiation is needed
What factors increase spatial resolution in mammography?
Five
- Compresssion
- AEC location
- Grounded metal tube
- Image receptor design
- Small focal spot/anodeangle
Would an increased SOD cause more or less dose?
Less dose
How do we calculate the end result of dose in mammography?
Mag dose=contact dose
What affect does magnification have on spatial resolution? Why?
Increases SR-there is more pixels per area of tissue
What are the pros of magnification in mammography?
- Increased SR
- Increased contrast resolution
- More photons per area of tissue
What are the cons of magnification in mammography?
- Increased skin dose
However we lower our technique to compensate bc of air gap technique increasing spatial resolution
How do we improve contrast resolution in mammography?
- Compression
- Beam E
- Grid
- Tube tilt
- Tube orientation
- Digital tomosynthesis
- Magnification
- Filtration
What is digital tomosynthesis?
-When the tube moves during the exam to create many images “slices”
What are the effects of digital tomosythesis?
- Increased dose
- Increased contrast resolution
What are the pros of film screen mammography?
Pros: HIgher spatial resolution and Low attenuation cassetes
What are the benefits of digital mammography?
-Higher contrast resolution
-No phosphor
