density decreases when grids are used, unless...
mAs in increased to compensate for the loss of scatter fog
subject contrast: tissue density
increase in tissue density decreases constrast owing to Compton effect
subject contrast: tissue thickness
as tissue thickness increases, contrast decreases owing to Compton interaction
spatial resolution or recorded detail
`sharpness which anatomical structures are displayed on an image receptor
uses fixed kVp while machine controls mAs; changing kVp doesn't change density, but change contrast
contrast improvement factor
measure the ability of a grid to increase contrast; ratio of contrast w/ a grid to contrast w/o a grid
ratio of primary radiation transmitted through the grid to secondary transmitted through the grid
grid conversion factor(GCF) or Bucky Factor
exposure increase is necessary to compensate for x-ray and scatter absorption
grid conversion factor or bucky factor pt2...
increase in mAs when converting from nongrid to grid...multiply mAs by GCF
grid conversion factor or bucky factor pt3...
decrease in mAs when converting from grid to nongrid status...divide mAs by GCF
moves back and forth during exposure; eliminate grid lines; move just before exposure and continue until just after the exposure
decreased density visible over the entire radiograph; absorb entire image-forming rays
air gap technique
uses increased OID; increased OID allows scatter to exit the patient and miss the image receptor
3 types of technique charts:
fixed kVp-variable mAs; variable kVp-fixed mAs; varible kVp-varible mAs
primary purpose of technique charts is...
radiation protection through decreased repeat exposure; more consistent image quality
fixed kVp-varible mAs assumes...
thicker parts absorb more rays and more rays must be placed in the primary beam
variable kVp-fixed mAs assumes...
thicker parts require a beam w/ shorter wavelength rays that are more penetrating
variable kVp and variable mAs assumes...
variations of pathological conditions, age, casts, contrast media
imaging plate (IP)
made of a photostimulable phosphor (PSP); remnant x-rays strike electrons in the phosphors, placing electrons in a higher state
direct detectors convert exit radiation...
directly into electrical charges, speeding image construction
each pixel corresponds to a shade of gray representing an area in the patient called...
a voxel (volume element)
a histogram (graphic display)...
is constructed to show the radiographer the distribution of pixel values(indicating low, proper, or high exposure)
information can be manipulated through various postprocessing steps...
subtraction, edge enhancement, contrast enhancement, and black/white reversal
postprocessing can compensate for overexposures or underexposures of considerable degree...
-100% to +500%
changing window level to adjust image brightness throughout the range of densities is a what type of relationship...
direct relationship; change image brightness
changing window width to adjust contrast is what type of relationship...
inverse relationship; changes contrast
look-up table (LUT)
histogram of brightness level values from image acquisition that can be used to correct, or enhance, luminance values
digital imaging and communications in medicine; it's used for blending PACS and various imaging modalities
visible differences between any two selected areas of density levels w/in the radiographic image
processing algorithm(math formula)...
used by the computer to reconstruct the image specific to the examination that was performed