Ch.18- The Grid

finuyubu's version from 2017-09-04 08:00

Section 1

Question Answer
kVp increases, scatter _________increases
kVp increases, __photons that don't interactincrease
What does scatter add to the film?density and IR exposure
What is the purpose of the grid?improves contrast by absorbing scatter
When do you want to use a grid? 2 rules:1. part thickness above 10 cm 2. kVp above 60

Section 2

Question Answer
What is the grid made of?series of radiopaque lead strips, and interspaces that are radiolucent
What are the radiopaque strips made out of?lead
Why is lead used?high atomic number, absorbs scatter, dense
What are the radiolucent interspaces made out of?aluminum, sometimes plastic fiber
Why is aluminum used?absorbs am. amount of scatter, absorbs part of primary beam
Who invented the Grid?Gustave Bucky
Who invented the Bucky?Hollis Potter

Section 3

Question Answer
What is the purpose of the bucky grid?to blur out the grid lines
Reciprocating bucky grid designmoved by a motor
Oscillating bucky grid designmoved by a electromagnet in a circular pattern
What happens when a moving grid fails?grid lines appear

Section 4

Question Answer
High quality grids will attenuate how much scatter radiation?80 to 90%
What is the grid ratio?height to distance of lead strips, it influences the grids ability to improve contrast
Increase lead content, _________ scatter absorbed, _________ contrastincrease, increase
If distance decreases, grid ratio _________increases
If distance increases, grid ratio _________decreases
Do high or low grid ratios clean up more scatter?high
Is a grid ratio of 16:1 or 8:1 going to clean up more scatter?16:1

Section 5

Question Answer
What is grid frequency?number of grid lines per in or cm
If there are less grid lines is it a grid with high or low frequency?high
increase grid frequency, grid ratio _________decrease
Increase grid frequency, (thicker or thinner) interspace stripsthicker
increase grid frequency, _________ techniqueDecrease
Grid frequency formula GF=10,000/(T+D)

Section 6

Question Answer
What are the 3 factors in grid performance?contrast improvement, bucky factor, grid selectivity
Contrast improvement factor formulacontrast with grid/ contrast without grid
The higher the K factor the _________ the contrast improvement (higher or lower)higher
What is the bucky factor/ GCF?amount of increase radiation needed to produce the image
GCF formulamAs1/mAs2=GCF1/GCF2
Increase kVp, _________ grid ratio, _________ GCFincrease, increase

Section 7

Question Answer
If a grid absorbs more primary radiation than scatter radiation this is known to have a higher degree of _________grid selectivity
Selectivity formula%primary transmitted/ % secondary transmitted
Increase grid ratio, contrast improvement factor _________increase
Increase grid frequency, contrast improvement factor _________decrease
heavy grids have _________ selectivity and _________ contrast improvement factorhigh and high

Section 8

Question Answer
Linear patternone direction, allow angulation of the tube
Criss cross patterncleans up more scatter, most restricted
Two kinds of linear:focused and parallel
Focusedmatches the divergence of the x ray beam
If lines were extended in a focused grid they would connect with a line called convergence

Section 9

Question Answer
What type of relationship does mAs and GCF have?direct
What type of relationship does density and GCF have?indirect
How does the air gap technique work?increase OID, which decreases scatter