Final Flashcards
QC limit of kVp calibration
measured kVp should be w/in 10% of indicated kVp
Breast cancer
about 80% occurs in ductal tissue (1/8 women)
ability to detect differences in brightness levels
contrast perception
how does moire artifact appear on XR?
appears as diagonal lines all across the img
should complete a visual checklist on a monthly basis
mammographer
how to reduce quantum mottle?
+ mAs
What is a moire artifact, what causes it?
when grid lines & scanning lasers are II; or during frequency harmonics/matching (when grid frequency gets close to laser scanning frequency)
advantages of slip ring?
contin. rotation of XR tube; transfers electrical power, scanning; instructions, & detected signals btw stationary components & rotating gantry components; eliminate need to stop rotation of gantry after ea. scan (no cables); led to development of helical/spiral (volume) scanning
How much total filtration is used in radiographic machines?
min. of 2.5 mm AL
used for evaluating diffuse reflection (light randomly scattered on the digi. display monitor); tested under ambient condition or total darkness; anti-reflective coating can min. reflections
TG 18 AD
mammograms are taken w _________ cassettes
single screen
most mammographic systems now have a moving grid w a ratio of
5:1
In DF, spatial res. is determined by:
img matrix & size of I.I.
controls img brightness determines the CT # that will be the center of the WW
window level (WL)
most QC testing on equipment done
annually
(neg. charged) focuses e- stream on the output phosphor
electrostatic lens
total D XR tube travels during actual exposure; there’s an inverse relationship btw exposure angle & section thickness
exposure angle/amplitude
how do pi lines appear on XR?
small marks on XR ≈ 3.1416” apart; appears perpendicular to the film’s direction of travel
Slip ring technology ?
replaced tangling high tension cables
acceptable level of distortion in primary class devices is
2%
2nd gen beam?
fan
the region of interest illustrated in the img and is reconstructed from the complete set of raw data
display/reconstruction FOV
centering indicator: must be accurate to
1% of SID
What is the device used to measure screen film contact?
wire mesh test (performed semi-annually)
detectors for 4th gen CT?
Multiple encircle pt; fixed ring of 4800 detectors
total D XR tube travels
tomographic angle/amplitude
mammography uses an anode angle of
23º
electronic noise in digi mammo can be reduced by
cooling detector
splits body into equal front and back halves
midcoronal
input phosphor f(x)?
converts XR energy into vis. light
Learn how to calculate pitch.
pitch = length of table travel per rotation/slice thickness
detectors for 2nd gen CT?
Multiple ≈ 30+ along a line
responsible for selecting the medical physicist & mammographers responsible for QC; responsible for supervising QA; supervisingQA program; oversee activities of team members; supervising pt communication/tracking
radiologist
tube movement for 3rd gen CT?
tube & detectors rotate; rotate continuously around the pt for 360º
scan T for 1st gen CT?
4.5-5 min./img
what causes static marks?
from friction or humidity lower than 40% caused by buildup of e-’s in emulsions
Advantages of volume scanning
multiplanar reconstruction shorter scan T reduced motion artifacts
Who invented CT?
Godfrey Hounsfield
Use of Breast compressions on mammography
use increases contrast & spatial res. lowers pt dose reduces motion blur reduces superimposition reduces focal spot blur
performs annual performance eval.’s of equipment, consults w/ mammographers concerning QC, review QC records to check for compliance; avg glandular dose to mammo pt’s must be tested annually by medical physicist
medical physicist
QA?
deals w ppl
How can you improve the spatial resolution on a mammographic image?
breast compression
QC limit for film illuminator
should not vary more than 10% (viewbox illumination)
volume scanning aka?
helical/spiral CT
how many detectors for 1st gen?
1; single
scan T for 3rd and 4th gen CT?
< 1 sec./img
mammography uses a tube tilt of
6º
frontal plane
coronal
What is the true size of a lesion if its magnified img measures 3 cm and the magnification factor is 1.5?
2.0 cm
What control the slice thickness of a tomographic image?
tomographic angle determines section thickness as angle increases, tomographic section becomes thinner (decreases)
What are the devices used to measure focal spot size?
pinhole camera star camera slit camera
mammo QC team?
radiologist, medical physicist, mammographer
a process where scattered rad. in the form of XRs, e-’s, and particularly light can reduce the contrast of the I.I. tubes
veiling glare
single picture element of the matrix 2D representation of the 3D volume of tissue in CT slice
pixel
What are the various types of static marks?
tree, crown smudge
median plane
sagittal
small display FOV (on magnification)
(zoom) restricts area of interest & displays anatomy larger; increases noise & in-plane spatial res.
f(x) output phosphor
interaction w e- stream produces light photons of much greater intensity than was produced at the input phosphor
Mammography currently uses ?
single-emulsion film
What is quantum mottle?
(noise) grainy img from insufficient mAs
used to perform a qualitative eval. of the luminance response (refers to relationship tw displayed luminance & input values of a standardized display system) of a digi. display device; evaluated from D of 30 cm
TG 18 CT
determines area over which projection data is collected; determines # of detectors collecting data for particular scan
scan FOV
spatial res. is limited by
pixel size
purpose of QA program is to maintain max. ___________ w min. ___________
quality mammograms; pt dose
tube movement for 1st gen CT?
tube & detector move linearly/ then rotate 1º - arc 180º; translate rotate scanning motion
(CT) scout aka?
scanogram or topogram
imaginary pivot point that the XR tube & IR move around; area of interest
fulcrum
range of CT #s that are displayed shades of gray controls the displayed img contrast
window width (WW)
QC limit for backup timer
should terminate the exposure at 6s or 600 mAs, whichever occurs first (or 1.5x’s original exposure)
calculate total brightness gain
total brightness gain = magnification gain x flux gain
how do guide show marks appear on XR?
thin lines on the leading/trailing edge of a film; parallel to the direction of film travel thru processor
attracts e-’s emitted by neg. photocathode
anode
QC?
deals w instrumentation & equipment; monitoring of equipment performance
photopic vision
use cones for daylight vision (intense light levels); cones have better visual acuity (perceive smaller objects better) & contrast perception than rods
splits body into equal L and R halves
midsagittal
photocathode materials?
cesium and antimony compounds
calculate minification gain
minification gain = diameter of input phosphor^2/diameter of output phosphor^2
Qc limit for collimation light
misalignment should not exceed 2% of SID
scan T for 2nd gen CT?
20 sec./img
What is a scout in CT?
preliminary img of the area being examined
materials for input phosphor?
cesium iodide crystals
factors that affect spatial res. (amount of detail present in an img)
phosphor layer thickness pixel size diameter of laser beam
the first rad. exam of the breasts obtained before 40 yrs use it for comparison of all future mammograms
baseline mammography
detectors for 3rd gen CT?
Multiple > 750++ along a curve; 960 detectors (curved array)
What causes PI lines?
bc of dirt/chem stain on a roller sensitizes the emulsion
splits body into top and bottom halves
axial - horizontal plane
What is volume scanning
XR tube rotates continuously around the pt as the pt/table increment through the gantry at selected speed
identify pincushion & barrel-like (geometric - affect relative size/shape of img features) distortions; used to eval. display res
TG18 QC
where XR & IR move about a fulcrum to obtain an img of a specific layer of tissue or an object that is superimposed by other tissue/objects; blurs structures above/below a specific plane
tomography
QC limit for exposure reproducibility
rad exposure should be reproducible to w/in 5%; output rad intensity should not vary more than 5%
distance indicator: must be accurate to
2% of SID
a min. of ____ mammograms must be included in a repeat analysis
250
mammo done symptomatic pt’s or ones w high risk factors (family hx) 2-3 views
diagnostic mammography
acceptable level of distortion in secondary class devices is
5%
plane in which target anatomy is clear/in focus; controlled by level/height of the fulcrum
focal plane: (object plane)
factors that control the brightness of the image in fluoroscopy
anatomy being examined kVp mA
it is essential that a small focal spot be used in ____________ to preserve img detail
magnification radiography
What are the formulas used for calculating magnification factor?
MF = img size/object size MF = SID/SOD
calculate flux gain
flux gain = # of output light photons/# of input XR photons
scotopic vision
use rods for night vision (low light levels)
tube movement for 4th gen CT?
only tube rotates; rotate continuously around pt for 360º
tomography w a tomographic angle of 10º or less, section thickness will be very large; used when the subject contrast is so low that a thin section tomo would result in poor img; most often in chest & renal exams
zonography
structure of an image intensifier (I.I.)
- Metal Housing 2. Vacuumed Glass/Metal Envelope 3. Input Phosphor 4. Photocathode 5. Electrostatic Lens 6. Anode 7. Output Phosphor
volume element; depth of a voxel is defined by the ‘slice thickness’
voxel
If the img size of an object is 3 cm and the magnification factor is 1.5 then what is the actual size of the object?
2.0 cm
the reduction in brightness at the periphery of an img
vignetting
1st gen beam?
pencil
QC limit for exposure timer accuracy
accuracy of 5% of the indicated exposure T for exposures greater than 10 ms; accuracy of 20% for exposure T less than 10 ms
trajectories used: (5) (tomography)
linear - least blurring of structures circular elliptical trispiral - produce max. blurring of unwanted structures hypocycloidal
disadvantage of mag rad:
increased pt dose (2x’s dose)
photocathode f(x)
emits e-’s when stimulated by light from the input phosphor (photoemission)
3rd gen beam?
fan
Target materials used in mammography and its advantages?
Molybdenum (Mo): 19 keV; used for smaller breasts Rhodium (Rh): 23 keV; increased penetration so used for thicker/larger breasts; (both reduce scatter)
The radiologist has requested that the images for a cerebro angio be magnified 100%. where would you set the SOD of the head if the SID is set at 20”?
10”
tube movement for 2nd gen CT?
tube & detectors move linearly/ then rotate 5º + - arc 180º; rotate translate scanning motion
mammo done on asymptomatic pt’s 50+ yrs min. of 2 views
screening mammography
QC limit for exposure linearity:
must be w/in 10% of the adjacent mA stations; mR/mAs value must be w/in 10% of adjacent mA stations
CT numbers, what number represent air, water, bone?
air: -1000 water: 0 bone: +400 —> +1000
large display FOV (on magnification)
displays anatomy smaller; reduces noise & in-plane spatial res.
used for the measurement of the res. of a display system helps point out any gross deviation in luminance adjustment
SMPTE pattern
materials for output phosphor?
zinc cadmium sulfide
What causes guide shoe mark?
caused by misalignment of the processor turnaround assembly (processing artifact)
max. non-uniformity of a display device should be
< 30%
