mammo Flashcards
mammo beam quality
HVL is ~0.3 mm Al
mammo matrix size
4096x6144
2 bytes/pixel
50 MB
mammo resolution
7 lp/mm
SID
65 cm
what does increasing breast thickness by 10 cm do to average glandular dose?
doubles it
cancer detection in mammo
4/1000
ACR phantom pass
4 fibers
3 specks
3 masses
mA for mammo
100 mA contact mammo
25 mA magnification
what interaction dominates in mammo?
PE
Compton dominates in other radiography
breast bipsy angles
+/- 15 degrees
mammo HVL
0.5 mm Al
grid factor factor in mammo
5:1 vs 10:1 for most other radiography
could also use air gao
focal spot in mammo
0.1 mm magnification mammo
0.3 mm contact mammo
pixel sizes mammo
50-100 um
tomosynthesis arc
arc is 15 degrees with image at each degree
shows lesions in given plane
power loading in mammo
3 kW contact mammo
1 kW magnification mammo
100 kW CT
mammo digital vs screen film resolution
7 lp/mm vs 12 lp/mm
-but digital mammo has better contrast resolution
-clinically they were found to be equal in efficacy
SID effect on focal spot blur
reducing SID increases focal spot blur
requirement for average glandular dose for 4.2 cm thick breast
<3 mGy/image with grid, <1 mGy/image without grid
-for breast with 50% glandularity
left and right breast DONT get added together into total dose
-if each breast gets 3 mGy, patient dose is 3 mGy
size of average compressed breast
60 mm thick, 15% granularity
semi-annual mammo QA items
dark room fog
screen-film contact
compression
QA tests in safety code 35
-reproducibility
-AEC
-linearity |x1-x2|</=0.1(x1+x2)
-HVL
-max exposure rate for fluoro
limiting factor for detecting microcalcifications
signal difference to noise ratio
focal spot size deviation
focal spot size gets smaller away from chest wall
why is cathode in mammo at chest wall?
to account for heel effect
GRID RATIO IN MAMMO
4:1
material is carbon not Pb
moving grid
grid moves while you acquire so you don’t get image of grid lines in image
benefits of using compression
-reduce background
-reduce scatter
-reduce motion
-reduce attenuation (ie lower dose)
pros and cons of using magnification
-can gain more resolution because you spread over more pixels
-results in more blurr, but can compensate by using smaller focal spot
-if you use smaller focal spot, magnification yields better MTF
-reduces scatter radiation, removes need for grid
-however smaller focal spot= longer exposure time. Can get more motion blurr
are parrallex and crossover issues in mammo?
no because mammo only uses 1 screen
entrance skin exposure in mammo
500-1000 mR for 4.5 cm breast
-with kV constant, increasing 1 cm in thickness requires 2x mAs and 2x skin dose
direct amorphous Se detector
-no blurring
-xrays strike Se- electrons are released and travel to the detector under E field
indirect flat panel detector
-CsI converts xrays to light- detected by flat panel detector
-detector elements build up charge when exposed to light
charged coupled device
-light released by screen is focused onto CCD by fiber optic tapers
-visible light falls on pixel- electrons are liberated and stored in each pixel
higher DQE, flat panels, CR, or screen film?
flat panels have higher DQE than CR and screen film
formula for mammo HVL
HVL > kV/100+ a constant
constant is 0.03-0.3 mm
MRI vs mammo
-MRI more useful than mammo for detecting invasive breast cancer
-less useful for micro-calcifications
US vs mammo
US cannot detect microcalcifications. It can:
-distinguish solid lump from cyst
-guide biopsy needle
-detect met. in lymph nodes
mammo imaging parameters
25-34 kVp, 100 mA, 1-2 s
mammo power rating
3 kW
In mammography, breast compression typically reduces the scatter-to-primary (i.e., unscattered) ratio from _____ to _____. A. 0.8–1.0; 0.4–0.5 B. 0.6–0.8; 0.4–0.5 C. 0.8–1.0; 0.1–0.2 D. 0.6–0.8; 0.1–0.2 E. Breast compression does not improve the scatter-to-primary ration at all, but simply serves to reduce motion blurring by immobilizing the breast.
0.8–1.0; 0.4–0.5
Breast compression minimizes the path length of x-rays through the breast and, therefore, reduces the likelihood of Compton scatter of the x-rays. As a result, breast compression typically reduces the scatter-to-primary ratio by about one-half, from 0.8–1.0 to 0.4–0.5, and thereby improves image contrast and lesion detectability.
