physics Flashcards
mammo equipment uses what 3 target (anode) materials
molybdenum Mo
Rhodium Rh
tungsten W
system will choose ____ that is best for tissue type and thickness
the best target material
_____ will be automatically selected by your machine based on the thickness of the breast
filter type
filters are most often made of… (4)
molybdenum Mo
Rhodium Rh
aluminum Al
silver Ag
_____ material is inserted into the xray beam to enhance contrast
filter
2 types of filtration
inherent and added
composed of parts of the xray tube and tube housing
inherent filtration
thin sheets of metal inserted in the xray beam
added filtration
what is exit window of tube housing made of
beryllium
2 important roles of added filtration
removes soft energy photons which add dose
removes higher energy photons which reduce contrast
used to absorb scatter and improve contrast
grid
grids absorb ___% of scatter
75-85
the ratio of the height of the lead strips to the distance between the lead strips
grid ratio
high grid ratio= ______ image contrast and _____ patient dose
better,higher
grid ratio in mammo
3:1-5:1
2 types of grids used in mammo
linear/focused
honeycomb/HTC
3 benefits from good compression
uniform breast thickness
reduce blurring
reduce scatter; improves contrast
the compression paddle should not extend beyond the chest wall edge of the IR by more than __% when compressed on the average breast
1
the mammo light field is controlled by
paddle size
the light field will come all the way to the chest wall and not exceed any edge by more than __%
2
the radiation shield must have the equivalent attenuation of at least ____ mm lead at __ kVp to limit the operator’s exposure to below __ mSv a week
0.08
35
1
the area of the anode (target) bombarded by electrons. this spot never changes
actual focal spot
downward projection of the actual focal spot; dependent on the steepness of the anode angle
effective focal spot
the steeper the angle the _____ the effective focal spot and the ____ the detail
smaller, better
mammo tubes have 2 focal spots
large- 0.3mm
small- 0.1mm
refers to the intensity of the xray beam which is not uniform in all portions of the beam
anode heel effect
in the anode heel effect, the anode acts as a filter- we call this
self filtration
the xrays toward the ____ end of the tube have more intensity because they have less of the anode to travel through. the dose will be more at this end.
cathode
the xrays toward the ____ end are less intense because they have more of the anode to travel and are more absorbed. there is less dose at this end
anode
in mammo the tube is moved anteriorly in the tube head (closer to the patient). lead is used to block half of the beam from the lungs
half field geometry
controls the wavelength of the xray beam
kvp
penetrating power
kvp
influences contrast and exposure latitude
kvp
average kvp in mammo
25-35
a unit of radiographic exposure equal to the product of the mA and the exposure time in seconds
mas
used to control the image blackening
ma
typical mA selection
20-100
typical time selection
.4-1 second
2 types of radiation are produced when electrons hit the anode
characteristic, bremsstrahling
xrays produced are confined to 2 energy spikes. the energy spikes will be determined by the anode material. this radiation is most important for determining xray beam penetration and giving up optimal contrast
characteristic radiation
xrays produced with multiple energies. this is the most common type of radiation produced
bremsstrahling radiation
the max permissible dose for one view of an average breast is ___mRad or __mGy
300
3
the distance between the xray source and the image receptor
source to image distance SID
average mammo SID
65-66cm
the distance between the object to the imaging receptor
object to image distance OID
an increase in OID will result in what
mag
mag increases the possibility of unsharpness so we use the small focal spot to gain detail; this ____ the dose
increases
3 most common mag factors
1.5x
2.0x
1.8x
purpose is to ensure that mammo equipment meets FDA
mammography equipment evaluation MEE
purpose is to ensure that the xray field aligns with the light field; to ensure it allows for full coverage of the IR by the xray field but does not allow significant radiation beyond its edges; to ensure that the chest wall edge of the paddle aligns with the edge of the IR.
collimation assessment
how often is collimation assessment done
done for new units, relevant service and annually
how often is mammography equipment evaluation MEE done
completed after installation of new units and relevant service
purpose- a more detailed eval to monitor contrast delivered by detector
system resolution tests-modulation transfer function MTF
to ensure that the image acquisition chain is consistently producing adequate image quality, that artifacts are not clinically significant, and that the SNR and CNR are adequate
artifact evaluation
