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anatomy12
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Intensifying screens produce ______
a large amount of light photons when struck by xray photons
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what is the purpose of IS
amplify the incoming xray beam and reduce patient dose
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describe the construction of the IS
- composed of radiolucent plastic coated with phosphors that emit light when struck
- they are in pairs on the top and bottom of cassette so a fil can be put in between
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what are the four layers of the IS
- base
- reflective layer
- phosphor layer
- protective coat
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what is the active layer of the IS
phosphor layer
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what is the refelctive layer composed of
magnesium dioxide or titanium dioxide
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what are the characteristics of phosphors
- high atomic number
- high conversion efficiency
- appropriate spectral matching
- minimal phosphorescence
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what is conversion efficiency
what decreases as conversion efficiency increases
- the ability of the phosphor to emit as much light per xray photon interaction as possible per measurement of screen speed
- pt dose
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what is spectral emission
spectral matching
- an indication of the precise wavelength emitted by the phosphor
- ability to match the sensitivity of film to latent image matching color of light to film
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what are the two types of luminescence
fluorescence and phosphorescence
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what is another term for screen lag or after glow
delayed phosphorescence emission
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why are rare earths used
they offer increased speed w/ maintaining resolution, when compared to calcium tungstate screens
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list some rare earth phosphors
list their spectral matching
- gadolinium green
- lanthanum blue
- yttrium blue
- calcium tungstate blue
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what are the characteristics that film screens posses
same features as films
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how many lp/mm can the naked eye resolve
state the lp/mm for non screen detail par, and high speed screens
- 10-20lpmm
- non screen 100lp/mm
- detail par 15lp/mm
- high speed screens 7lp/mm
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how does film lose contact with screens
caused by foreign objects in the cassette and warped or damged cassettes
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what test is done to check for poor film screen contact
wire mesh test
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what is quantum mottle
happens when insufficient phosphor crystals emit light to expose a
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How can you reduce quantum mottle
increase mAs
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what factors can affect screen speed but not resolution
kvp and high temperature
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how can film speed be classified as three things
- intensification factor
- descriptive rating
- relative speed number
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what is the k-shell absorption edge
when incident xray photons match the K-shell binding energy of the phosphor ther is an increase in characteristic production within the screen
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what is an asymmetrical screen
screens that have increased quantum mottle resolution to show better detail
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what are some characteristics film cassettes
- front of cassette is radiolucent
- the IS screens are attached to the inside of the front and back of cassette
- rigid to support body parts and lightweight
- made with lead foil to reduce the residual beam and absorb back scatter
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what is the proper care of a cassette (4 things)
- when loading cassettes the tops should never be fully open
- cassettes sohuld be stored on end like a book
- screens should be cleaned with electrostatic cleaning solution
- never close a wet cassette
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what is an artifact
anything that blocks the transmission of light between the screen and film (dust or pitted screens, white spots)
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panchromatic films
orthochromatic films
- film that is sensitive to entire visible light spectrum
- ortho films only sensitive to green light
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define density/IR exposure
the amount of radiation that has exposed the IR
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brightness
is a monitor control function that can change the lightness and darkness of an image on a display monitor but it is not related to IR exposure
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is brightness interchangeable with density
no
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describe how density is related to IR exposure
the visibility of the image is the result of exposure to film in both film and DR
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window level
window width
- describes digital post processing that produce changes in brightness
- contrast
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what is the controlling and influencing factor of density
mas and kvp
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what are various terms for contrast
- short scale
- high contrast
- increased
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what is subject contrast
what is the dependent on
- the range of differences in the intensity of the xray beam after it has been attenuated by the subject
- kvp and the type of irradiated material
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what are the two photographic properties that comprise the visibility of detail
contrast and density
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high contrast factors are good for what studies
soft tissue studies
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image receptor contrast deals with what
h&d curve
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what is changeable in a fixed kvp system
what is changeable in a variable kv system
- mas changeable kv is fixed
- kvp is changeable mAs is fixed
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recorded detail
- one of the two geometeric properties of radiographic image quality
- it is the degree of geometric sharpness or accuracy, spatial resolution of the structural lines recorded in the xray image
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spatial resolution
how do we measure spatial resolution
- deals with objects being closer together
- using point spread function
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spatial frequency is measured using what
modulation transfer function
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what is the unit of resolution for primary film/screen
lines per millimeter
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matrix size:
pixel size:
gray scale:
- a square of series of boxes that gives form to the image
- picture elements; individual matrix boxes
- the number of shades of gray in a radiographic image
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what is image noise
bg information the image receptor receives
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nyquist criterion:
aliasing:
- it is when digital imaging requires spatial resolution info to be sent/sampled over twice from each cycle
- this is what compares the spatial frequency if it is not the same as nyquist criterion and the data sampled are less than twice per cycle then the image is changed with cauderoy lines
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what causes the cauderoy lines on an xray
moire effect = from aliasing
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penumbra
umbra
- geometric unsharpness
- sharp area of a shadow
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geometric factors
receptor factors
motion
- geo factors = FSS Distance OID,SID
- recep. factors = Film/screen systems, digital systems
- motion = voluntary involuntary equipment
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what other terms mean detail
- sharpness definition
- spatial resolution
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what is the geometric unsharpenss formula
FOD is the same as ___
OID is the same as ____
how do you find FOD
- FSS * object -film-distance or OID/FOD(focus object distance)
- SOD
- OFD
SID - OID = FOD or SOD
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what is the density maintenance formula
m2=m11*g2g1(Grid factors)*S1S2(Film Speed)*D2(squared)D1(squared)*K
- if there is a 15% increase in kv (*1/2)
- if there is a 15% decrease in kv (*2)
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list the grid conversion factors
- no grid 1
- 5:1 2
- 6-1 3
- 8-1 4
- 10-1 5
- 12-1 5
- 16-1 6
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dynamic range
the concept of contrast as it is displayed on a soft copy monitor for digital images, range of density/brightness of the display monitor light emission
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define contrast
one of the properties that comprise visibilty of detail; the difference between adjacent densities
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what are three ways resolution can be measured
through the lines per millimeter, line spread function and modulation transfer function
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