chapter 20-21 Flashcards
what are the causes of scatter radiation
- high kVp
- large field size
- large part thickness
difference between scatter and blur
- scatter is completely random and blue is geometrically predictable
what does scatter affect
image visibility:
- exposure
- subject contrast
- noise
function of the grid
absorbs scatter radiation that has already been produced in patients body before it reaches the IR
what eliminates grid lines
potter-bucky diaphragm
what is the grid ratio
ratio of the height to the width of the interspaces between the lead strips
field size has a greater impact upon…
scatter radiation
what are the indications for grid use
- thickness of soft tissue
- size of the field
- kvp used
what is the ratio of primary radiation transmitted through the grid to scatter radiation transmitted through the grid
selectivity
body parts thicker than ____ require a grid
10 cm
what is the grid conversion factor formula
mAs1/ mAs2 = GCF1/GCF2
what do grids affect
visibility functions
grid lines can be minimized using which 3 things
- proper distance
- proper alignment
- potter-bucky diaphragm
what is canting
the tilting of lead strips
what is the distance from the lead strips to focal spot
grid radius
which grid involves the lead strips to be tilted as they move away from the center of the grid
focused grids
which grid has no tilting
parallel
the grid radius for a parallel grid is…
infinity
what causes an asymmetrical loss of exposure
tilting the grid, misalignment, angling of the beam
what is the anode bevel
angle of the target surface to the anode
anode bevel affects…
- line focus principle
- anode heel effect
what is the line focus principle controlled by
- width of electron beam to filament
- angle of anode bevel
the line focus principle makes it possible to achieve a…
small effective focal spot and maximum sharpness
what is the anode bevel of standard x-ray tubes
15-17 degrees
