Lecture 8- Mammogram Flashcards
what color is fat on mammogram
dark
what color are the glands on mammograms
light
what are you looking for in mammogram
look for micro calcifications, compare to last two years and subtle differences in the tissue
what is the use of Z in mammogram and what is the usual Z for it
adipose, glandular, fibroadenoma, ductal carcinoma, between 5.3 and 5.8- need to maximize the difference between breast tissue to get the best image
which of the 4 x-ray interactions should be maximized for mammography?
photoelectric effect
why is the photoelectric effect important to mammography
it helps to distinguish different Z so it helps with small differences. You want to vary the energy and low energy X-rays. The interaction probability is proportional to Z3/E3
what is the interaction probability of compote scatter
I/E
what is the typical kVP of typical radiography and typical mammography
typical radiography is 70-100 and typical mammography is 25-30
draw a mammography Xray beam
draw it
what is the difference between a diagnostic and screening mammogram
the screening has lower radiation because its a screening test. It needs to image micro calcifications less than 100
draw a mammogram X-ray tube
what is different
does mammogram use half filed or full field and draw the breast in it
half field
why does it use half-field
it uses half field to that it is perpendicular to the chest wall which is important because it gets the better image of the breast
what are the three anode materials for mammography
molybdenum, rhodium, tungsten
what is the Z of molybdenium
Z=42 and it is the traditional mammography anode material
what is the Z of rhodium
Z=45 like Mo
what is the Z of tungsten
Z=74 and it is also a typical radiography anode material
what are the spikes on an output to energy spectrum and what is the continuous part called
spikes are characteristic Xray
tube filtration- what is it and what does it do
an added later of metal at the tube port and it is to selectively remove some x-rays to modify the x-ray beam spectra
what is different about the mammogram filter vs. normal
there is an additional ilter
what causes the discontinuity in the attenuation coefficient for Mo, Rh, and Ag
K edge absorption
what is the k edge absorption
probability of the photoelectric effect increases sharply when incident X-ray energy is just greater than the binding shell energy
what is the use of the mo filter K-edge
forms a window to remove low and high energy x=rays leaving Mo characteristic xrays
what is Rh better for
higher energy X-rays for more penetration of thicker tissues
what are M anode used for
higher energy X-rays and higher tube loading for tomosynthesis.
what filters can be used for mammography
Rh, Ag, and Al
what shell is removed with mammography
L shell cray are at 10kev remove the L shell
what is a typical HVL for mammography system
.3 and .4 mm Al at 30 kvp, 1-2 cm in breast tissues
when is the HVL higher for Z anode and filter
Mo/Mo
what are grids used for
scatter rejection in contrast imaging. Common grid specifications, Moving bucky to blur grid shadow.
what is the best grid ratio
4:1 and 5:1 bucky factor is 2 ro 3
compare mammogram focal spot size to radiography
.3/.1 mm and 1.2/.6mm
compare mammogram KVP to radiography
25-30 KVP and 50-120KVP
compare mammogram mA to radiography
LFS:100 and SFS: 30 and 200-800
compare mammogram exposure time to radiography
1-2 seconds and .1-.5sec
compare mammogram grid ratio to radiography
4:1-5:1 and 6:1-16.1
is magnification used in mammogram and if so, when
there is no magnification in screening exams, but if a questionable lesion is found, a diagnostic examination is conducted. Magnification views may be required where investigation or masses or better delineation of calcification is needed
what adjustments are made when using geometric maginification
magnification factor of 1.5-2 and spot impression paddle with small focal spot size selected (.1mm)-mA reduced to 30 mA. No grid used because air gap reduces scatter that reaches the detector
what happens to the penumbra as the geometric magnification increases
increases
what are the advantages of geometric magnification
increases conversion for reduced overlapping tissue, improved
what are the disadvantages of geometric magnification
smaller imaging field and increased patient motion artifact
is screen film for mammography single or double sided
single sided
what is most commonly used for CR mammogrpahy
dual sided CR and imaging pates and dual sided readout. Smaller pixel side.
what are the main differences forflat panel detectors for mammography
smaller size, smaller izel size, and AEC method
AEC in mammography
for screen field and CR image receptors, AEC uses a phtootimer sensor and voltage comparator similar to radiography.
what changes for flat panel mammography
it is a short 50 ms exposure so it is not using a sensor
what is a photon counting slit scan system
it is single photon detection eliminates electronic noise. Detector arranged as a line that scans across breast. X-ray beam colimated to a slit pre and post patient to minimize the scatter. 3-15 time
what is a digital mammography display
it is high resolution with 5 Mpixel compared to 2-3 pixel for radiography. there is high luminance of 300-1000 as compared to 200-300 of normal radiography.
what is some of the special image processing for digital mammography
skin line enhancement and equalized image density
what is the formula for the average glandular dose
Dg=dgN time Xesak
where Vesak- entrance skin air karma
DgN- average glandular dose conversion factor, which is determined from Monte Carlo simulations of photon interactions within models of breast tissue
what causes DgN to increase
photon energy
what causes DgN to decrease
breast thickness
who regulates the mammography
mammography quality standards act, which is through the american college of radiology or some individual states. Includes personnel requirements and quality control tests and sample clinical images. provided by the FDA after accredidation. Includes annual facility inspection.
what aspects are included in physics equipment evaluation
collimation, system resolution, AEC performance, artifact evaluation, image quality evaluation, beam quality (HVL), and breast dosimetry.
what is the minimum phantom count to pass image quality standards
minimum is 4 fibers, 3 speck groups, and 3 masses. Artifacts that look like the object are subtracted from the count
what is used to quantify image quality for these tests
SNR and CNR
what are the qualitites of the breast phantom
mimics standard breast attenuation, thickness of 4.2 cm, 50% glandular/50% adipose tissue equivalent
what is used to measure breast dosimetry
measures entrance skin air karma that is used for 4.2 cm 50% glandular breast for that clinical site. Calculate Dg regulatory upper limit is 3mGy
what is breast tomosynthesis
it is an X-ray tube and fast detectors that swing at a specific angle
what are the imaging equipment requirements for breast tomosynthesis
xray tube and gantry automated angled movement, fast readout digital detector, high power and heat loading x-ray tube, and higher beam energy to reduce patient dose
is tomosynthesis available on all systems
no it depends on the provider
how are images reconstructed for tomosynthesis
they put the images together from the different angles like a CT scan
what is synthesized 2D mammogrpahy
it is an mage constructed from tomosynthesis
what are the benefits to the 2D synthesized from the tomosynthesis
reduces dose, and reduces exposure time in compression.
what measure is used is synthesized 2D mammography
created as a maximum intensity projection of slice dataset
are there differences in sensitivity and specificity for tomosynthesis and 2D images
no there are not
what happens if the collimator clips at the chest wall
colimator blade field extends no more than 2% SID beyond image receptor edges at the chest wall is positioned in too far. Blurred edge indicates obstruction is magnified near the x-ray tube.
what are the MQSA requirements for chest clipping
no collimator clipping the chest wall. x-ray
what happens with grid artifact
grid should be moving during he exposure so that the lines can be blurred artifact is subtle if the motion is partial
what is cross-hatch grid
unitque mammography grid because it is high transmission cellular grid. Grid should be moving during exosure
what is a ghost image
it is a residual signal from previous image. Direct detector loses sensitivity in areas of high exposure due to retained trapped charge
how do you fix issues with ghost image
longer wait time between exposures and manufacturers modified detector readout sequence thing to reduce trapped charge
what is a tomosunthesis artifact
it is artificial low density surrounding high density objects along the scan direction which leads to a halo artifact due to limited angular range in acquisition
what is used to fix tomosynthesis artifact
various reconstruction algorithm modifications have been proposed to reduce appearance. Based on removing high contrast object from the projection images prior to reconstruction, then adding back into slice images
what is the zipper artifact/cause
out-of-plane high contrast object is visible as zipper artifact along the scan direction caused by limited angular range in acquisition sweep.
how do you resolve the zipper artifact
various reconstruction algorithm modifications have been proposed to reduce appearance. Based on removing high contrast object from the projection images prior to reconstruction, then adding back into slice images
what is the staircase artifact
limited angular range in acquisition sweep results in staircase artifact at edge of field
how do you fix the staircase artifact
same solutions as halo arifact reduction
what causes false calcifications on 2D image slice
overlapping dense ligaments in the slice images combine to appear as calcifications
how do you resolve false calcifications
modifications of the 2D image synthesis algorithm
