Chapter 5 Rad 2 Flashcards
Scatter is the result of?
Compton
What results from an interaction with an outer shell electron?
Compton
What are the end results of compton?
Weakened X-ray photon, Gray on radiograph
what is another name for Compton?
Recoil Electron
2 factors affecting the amount of scatter reaching the IR
kVp & Volume of tissue
Why does kVp and volume of tissue affect scatter?
the higher the kVp the more scatter, fatter scatter
as collimation decreases (increased field size) what happens to scatter, patient dose, contrast, and density?
Scatter= increases , patient dose= increases, Contrast= decreases, Density increases
as collimation increases (decreased field size) what happens to scatter, patient dose, contrast, and density?
Scatter= decreases , patient dose= decreases, Contrast - increases, Density= decreases
What is the first step in patient protection?
optimum collimation
significant collimation may require and increase or decrease in mAs?
increase (example L5-S1)
There is ___ unsharpness on the anode side of the tube?
less
There is ___ unsharpness on the cathode side?
more
What is the simplest type of collimator. Piece of lead with a hole in it. Not variable, and not used very much.
aperture diaphragm
What is shaped like a megaphone and correlates to divergence of the beam.
Cone
What is shaped like a tube and can extend down, used mostly for skull work?
Cylinders
Which is better cone or cylinder?
cylinder
What is the best type of variable beam- restricting device? has 2 sets of adjustable lead shutters and a light source for centering?
Box Type collimator
NCRP says collimation must be within __ of the SID
+/- 2 percent
How can you check collimation?
9 penny test
What years was it a law that all equipment manufactured had to have PBL installed?
8/1/1974-1994
Who invented the stationary grid in 1913?
Gustave Bucky
When do you use a grid?
when the part is 10cm or bigger & 60 kvp or above
Grid ratio formula?
height of pb strips/ distance between pb strips
Interspacing material can be Organic or Inorganic give examples of both
Organic= Carbon like balsa wood, cardboard Inorganic= Not Carbon like aluminum (usually used)
Grid frequency
of Pb lines/ inch or cm
how many PB lines are there usually?
60-110
The higher the grid ratio the ___ the cleanup
more
the higher the grid ratio the more the cleanup but ___ restrictive
more
Grid conversion formula
mas1/mas2 = gcf1/gcf2
this grid the Pb lines run in 1 direction only head to toe. Used most often. Can angle cephalic or caudal but not across the grid lines
Linear grids
this grid the pb lines run at right angles to one a noter. cannot angle in any direction. and most restrictive.
Crossed of crossed hatch
this grid the pb lines parallel to one another, have no set focusing sidtance
parallel or non focused
this grid angled lead lines to use in a specific focusing distance
focused
Where points converge in space from a focused grid
convergent point
Grids that lay on top of IR usually taped to IR
Wafer Grid/ Stationary Grid
Who invented the moving grid to blur grid lines?
Hollis Potter
What are the 4 types of movement with a grid?
Reciprocating, Recipromatic, Oscillating, Single-stroke/ Sling Shot
What is not a type of movement in a grid?
elliptical (tomo tube-travel pattern)
Grids _____ contrast
increase (by absorbing scatter)
Grids ____ pt dose
increase (because mAs is increased to maintain density)
Grid to non grid
divide
non grid to grid
multiply
complete peripheral grid cut off? (no exposure on outer edges)
upside down focused grid cut-off
when beam is angled across grid lines (most common, decrease in density)
off level grid cut off
bucky not shoved in all the way or tube off center
off center grid cut off
when SID is out of focusing range. acceptable density in center with decreased density on outside edges
off focus grid cut off
when stationary grid is used during CR. can be solved with a higher ratio stationary grid or use a moving grid. also occurs as a faulty attempt at making a cross hatch grid
moire effect/ zebra pattern
6’’ air gap = 6:1 grid does what to contrast and density?
increased contrast, decreased density
DR/CR more or less sensitive to scatter?
more
