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107 Cards in this Set
- Front
- Back
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What is the Z and K-edge energy of Mo?
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42; 20.0 keV
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What are the characteristic x-ray energies of Mo?
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17.9 and 19.5 keV
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What is the Z and K-edge energy of Ro?
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45; 23.2 keV
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What are the characteristic energies of Ro?
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20.2 and 22.7 keV
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Does Mo or Ro have higher characteristic energies?
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3 keV
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What is the normal focal spot size for mammography?
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0.3 mm
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What is the focal spot size in magnification mammography?
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0.1 mm
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What are the tube currents for the two focal spots in mammography?
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0.3 mm uses 100 mA
0.1 mm uses 25 mA |
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What is the x-ray tube window made from?
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Beryllium
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Is heel effect on the cathode or anode side?
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cathode
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What is the optimum x-ray energy level for mammography?
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19 keV
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How do higher energy photons cause detriment in mammography?
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Decrease contrast
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What are filters in mammography made from?
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Ro, Mo, Silver
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How thick are filters in mammography?
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30 micron
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What kind of radiation do filters remove in mammography with respect to the K-edge?
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Remove bremsstrahulng radiation above the K-edge
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Compared to a Mo filter, a Rh filter does what?
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Transmits more photons between 20 and 23 keV
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Compared to a Rh filter, silver filter does what?
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Transmits more photons between 23 and 25.5 keV
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What are the scatter to primary ratios in mammography?
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0.6 to 1.0
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Are scatter to primary ratios higher or lower than in general radiology?
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Lower
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What are typical linear grid line densities?
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50 lines per cm
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What are grid ratios used in mammography?
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5:1
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What is the Bucky factor in mammography?
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~2
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How does the use of a grid affect patient does in mammography?
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doubles it
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What are screens made of in screen-film mammography?
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Gadolinium oxysulfide
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What type of films are used to reduce receptor blur?
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Single emulsion films
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Mammography films have ____ gradients and ____ latitude?
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high; low
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What are optimal film densities in mammography?
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1.6 to 2.0
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Why are higher film densities required?
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Better film contrast
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What is a typical matrix size in mammography?
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3k x 4k
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What are the pixel sizes in mammography?
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~80 micron
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What is the size of the smallest microcalcification in mammography?
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150 micron
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How does compression affect x-ray tube voltages?
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Lower x-ray tube voltages can be used
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How does compression affect blur?
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Reduces it by putting tissue closer to the image plane
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What is the average size of a compressed breast?
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4.5 cm
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What is the typical current for contact mammography?
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100 mA
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What is the typical exposure time for contact mammography?
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longer than 1 s, up to 4 to 5 seconds for dense or thick breasts
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What is the half value layer in mammography?
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0.3 mm Al
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What is the typical x-ray tube voltage in contact mammography?
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25 kV
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What is the typical mAs?
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150 mAs
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What is the required air-kerma at the image receptor for contact mammography?
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0.2 Gy
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What is the typical generator power in contact mammography?
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3 kW
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What does magnification mammography improve visualization of?
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mass margins and fine calcifications
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How is magnification achieved in magnification mammography?
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Using a 15 to 30 cm standoff
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What is the magnification in terms of SID and SOD?
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SID/SOD
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What are typical SID, SOD, and magnification in magnification mammography?
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65 cm, 35 cm, and 1.86
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What is used to reduce scatter in magnification mammography?
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Air gap, a grid is not required
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How much does the absence of a grid reduce dose in magnification mammography?
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~30%
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How does exposure time in magnification mammography compare with that from contact mammography?
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3 times more
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What is the required luminence value for viewing mammograms?
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3000 candelas/m2
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What ist he luminence value of normal viewboxes?
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1500 candelas/m2
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How many megapixel monitors are required for viewing mammograms?
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Five megapixel
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What are the matrix sizes of digital stereotactic localization systems?
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512 x 512 or 1024 x 1024
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What is the pixel size of a 5 cm x 5 cm field of view of a digital sterotactic localization system?
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50 to 100 um
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How many degrees from normal are views of the breast acquired for digital localization?
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+/- 15 degrees
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How many projection radiographs are taken in digital tomosynthesis? What is the degree separation?
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15 images; 1 degree separation
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What is the nominal slice thickness in digital tomosynthesis mammography?
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1 mm
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How many mammograms over how many months are interpreting physicians required to have interpreted?
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200 mammograms over the past 24 months
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What are the five accreditation requirements for mammography?
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1. Site survey questionaire
2. Assessment of image quality using phantom 3. Dosimeter assessment of mean glandular dose 4. Assessment of clinical images by independent radiologists 5. Assessment of quality control program |
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How often must processor quality control be performed?
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Daily
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What is developed and what is measured in processor quality control?
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sensitometry strips; speed, contrast, base plus fog
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How often are screens and darkrooms cleaned?
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Weekly
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What is tested weekly?
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1. ACR phantom image
2. Scoring image quality, film background density, density difference 3. Assessment viewbox and reading conditions |
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What are quarterly tests?
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Repeat analysis
Fixer retention analysis |
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What is the tolerance of repeat rates in mammography?
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Between 2 and 5%
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What tests are performed on a semi-annual basis?
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1. Fog
2. Screen-film contact 3. Compression |
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How often is the QC program reviewed and by whom?
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Annually, by the medical physicist
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What is the training requirement of a medical physicist?
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Perform at least 6 annual medical physics surveys every 2 years
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What imaging tests are required to be performed by the medical physicist annually?
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unit assembly and cassette performance
collimation system resolution peak voltage accuracy and reproducibility beam quality (half-value layer) automatic exposure control performance uniformity of screen speeds radiation output entrance skin exposure and mean glandular dose image quality artifact evaluation |
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What does the ACR phantom contain?
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6 fibers, 5 speck groups, and 5 masses
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What is the minimum requirement that the phantom image must show?
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4 fibers, 3 speck groups, 3 masses
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What is the ACR requirement for average glandular dose with a grid?
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< 3 mGy per image
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What is the ACR requirement for average glandular dose without a grid?
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< 1 mGy per image
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What percent of absorbed x-ray energy is converted into light energy at the input phosphor?
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10%
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What is the input phosphor made from and what is its thickness?
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~300 um thick CsI screen
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Why are X-rays efficiently absorbed in CsI screens?
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Because the K shell binding energies of Cs and I are approximately 35 keV
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What does the photocathode emit?
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Photoelectrons
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What is the accelerating voltage across the II
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30 kV
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What is the output phosphor made from?
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ZnCdS
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What are the two components of brightness gain?
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Minification gain and flux gain
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What is the typical flux gain?
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50
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What is the conversion factor of modern IIs?
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10 to 30 cd/m2 per uGy/s
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What occurs as a result of of light scattered within the output phosphor?
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veiling glare
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How does electronic magnification affect skin dose?
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Increases it
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What is the typical pincushion distortion?
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3%
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How much is typical vignetting?
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< 25%
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What is distortion of the II with respect to local magnetic fields called?
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S-distortion
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Describe how scan mode in interlacing works.
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262.5 odd lines scanned in 1/60 second, then
262.5 even lines scanned in1/60 second |
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What is the advantage of interlacing?
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Prevents flickering
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What do European TV systems do with regard to scanning?
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625 lines and 25 frames per second
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In what scan mode is each line read sequentially?
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Progressive scan mode
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What is the advantage of progressive scan mode?
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Reduces motion artifacts
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What is characteristic of vidicon systems?
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High image lag, due to averaging sequential image frames
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What is characteristic of Plumbicon cameras?
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Less lag than vidicon
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How do CCD systems provide noise averaging?
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Digital recursive filtering
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How many bits is each pixel in TV?
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10 bits
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What are the modes used in HDTV?
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1280 x 720 in progressive scan mode
1920 x 1080 in interlaced mode |
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What is the aspect ratio of HDTV?
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16:9
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What is the maximum bandwidth of digital TV channels?
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19 Mbit
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What are tube currents of fluoroscopy?
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1 to 5 mA
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What are tube voltages in fluoroscopy?
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Between 70 and 110 kV
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What is a typical grid ratio in fluoroscopy?
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10:1
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At a given FOV, additional collimation ____ patient doses with no loss of image quality.
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reduces
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Pulsed fluoroscopy _____ the dose per frame to reduce the perceived level of random noise.
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increases
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What are x-ray tube currents when obtaining photospot images?
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300 mA
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What is the frame rate of cine images in digital cardiac imaging?
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15 frames per second
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What % contrast difference can DSA visualize in x-ray transmission?
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< 1%
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What is the matrix size of photospot images?
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1024 x 1024
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