QUIZ #4 {QUICK STUDY EDITION}

Question 1

3 main factors influencing production of scatter + rules for using a grid

(from most significant to least significant)

Answer 1

Patient or part thickness >13cm (more chance for scatter)

(large) field size

(extremely high) kVp

Question 2

Scatter affects density and contrast in what way

Answer 2

Scatter INCREASES density

Scatter DECREASES contrast

Question 3

15% rule to change contrast, and/or density or to maintained density

Answer 3

Slight lengthening of gray scale with maintained density (slightly denser due to penetration)

Question 4

Types of beam restriction?

Which is best and why?

Answer 4

• Aperture Diaphragms
• Cones/Cylinders
• Collimators
• Grids

Cylinders are best

DECREASE penumbra/blur, field size, & scatter

INCREASE contrast/detail/spatial resolution

Question 5

What is PBL?

Answer 5

Sensors in the Bucky that know the size of the IR and collimates to correct size (auto-collimation)

Question 6

Off-level grid error…

Answer 6

tube or grid is angled along so that the beam crosses the parallel grid lines, decreases density

Question 7

Off-center grid error…

Answer 7

when central ray is not centered correctly, increases cut off

Question 8

Calculation for grid ratio

Answer 8

h/D

height/Depth

THE BEST INDICATOR OF HOW WELL A GRID WORKS, HIGHER RATIO = HIGHER GCF

Question 9

How does grid ratio help us, what does it tell us?

Answer 9

Increasing grid ratios INCREASES the amount of scatter that is absorbed

Question 10

What is bucky factor or grid conversion factor? be able to use it in a calculation

Answer 10

A Grid Conversion Factor formula will assist in selecting the appropriate mAs, this will provide the correct exposure to the IR and prevent noise.

(How the mAs without a grid compares to mAs with a grid)

Question 11

What is grid frequency?

Answer 11

Number of grid lines per inch/centimeter

The higher the grid frequency, the LESS obvious the grid lines on an image

41-80 L/cm

Question 12

What special distance do we need to know with a focused grid?

Answer 12

Focal distance

Question 13

Upside-down grid error…

Answer 13

Seen with focused grid that is placed tube side down. Center will be exposed, with ~all being absorbed towards periphery.

Question 14

Upside-down grid error…

Answer 14

Seen with focused grid that is placed tube side down. Center will be exposed, with ~all being absorbed towards periphery.

Question 15

what is air gap?

how do we use it to our advantage?

Answer 15

Alternative to grid, used in magnification exams. OID is increased, causing air gap between patient and receptor.

Causes the amount of scatter that reaches the film to decrease.

Disadvantage is loss of sharpness from Increases OID (more magnification)

Used for lateral C-spines.

Question 16

what is air gap?

how do we use it to our advantage?

Answer 16

Alternative to grid, used in magnification exams. OID is increased, causing air gap between patient and receptor.

Causes the amount of scatter that reaches the film to decrease.

Disadvantage is loss of sharpness from Increases OID (more magnification)

Used for lateral C-spines.

Question 17

What is air gap?

How do we use it to our advantage?

Answer 17

Alternative to grid, used in magnification exams. OID is increased, causing air gap between patient and receptor.

Causes the amount of scatter that reaches the film to decrease.

Disadvantage is loss of sharpness from Increases OID (more magnification)

Used for lateral C-spines.

Question 18

What is the fulcrum?

Object plane?

Slice thickness?

How do we get thinner slices?

Tissue of interest should be positioned at the _____?

Answer 18

Fulcrum is the pivot point or point where the imaginary line connecting tube + receptor at start and end positions cross.

Object plane is the area surrounding the pivot point and tissue in this area is imaged ”in focus”

Tomographic angle describes the amount of tube movement and the slice thickness.

Greater angles = more thinness

Tissue of interest should be positioned at the FULCRUM

Question 19

What is the fulcrum?

Object plane?

Slice thickness?

How do we get thinner slices?

Tissue of interest should be positioned at the _____?

Answer 19

Fulcrum is the pivot point or point where the imaginary line connecting tube + receptor at start and end positions cross.

Object plain is the area surrounding the pivot point and tissue in this area is imaged ”in focus”

Tomographic angle describes the amount of tube movement and the slice thickness.

Greater angles = more thinness

Tissue of interest should be positioned at the FULCRUM

Question 20

Exposure times in tomo are _____ that of regular x-ray

Answer 20

Exposure times in tomo are GREATER than that of regular x-ray

Question 21

Know the types of tube movement and which produces the thinnest slices.

Answer 21

The greater the angle (linear arc) the thinner the slice

10°-40° range

Question 22

What are the 3 Prime Factors?

Answer 22

• kVp (primarily quality, but affects quantity. How penetrating the beam is. Higher kVp with denser tissue/material)
• mAs
• SID

Question 23

What controls quantity and quality in the image?

Answer 23

QUANTITY = mAs

QUALITY = kVp

Question 24

What primarily controls density and contrast in an image?

Answer 24

mAs

Question 25

What are the 3 main factors effecting technique selection?

Answer 25

• Thickness
• Composition
• Pathology

Question 26

For denser parts, we increase kVp/mAs

For thicker parts, we increase kVp/mAs

Answer 26

For denser parts, we increase kVp

For thicker parts, we increase mAs

Question 27

Describe detail and distortion and what controls each

Answer 27

DETAIL = seeing small objects, increased SID and collimation

DISTORTION = misrepresentation of objects, increased SOD

Question 28

What is the most common technique chart?

Answer 28

Fixed kVp

Question 29

What are variable kVp charts?

SHORT/LONG scale contrast?

HIGHER/LOWER patient dose?

NARROW/WIDE exposure latitude?

ADVANTAGES?

DISADVANTAGES?

Answer 29

A fixed mAs is used and kVp is varied to accommodate differences in thickness (historic, not used much anymore)

SHORT scale contrast

HIGHER patient dose

NARROW exposure latitude

ADVANTAGES:
• Allows for small changes in exposure for small changes in part thickness
• Higher contrast

DISADVANTAGES:
• More patient dose
• Higher repeat rate
• Increased Tube wear

Question 30

What are fixed kVp chart s?

SHORT/LONG scale contrast?

HIGHER/LOWER patient dose?

NARROW/WIDE exposure latitude?

_____ or _____ the mAs for every __cm of part thickness

ADVANTAGES?

DISADVANTAGES?

Answer 30

kVp is selected to provide proper penetration of the part, mAs is varied to provide adequate density.

LONG scale contrast

LOWER patient dose

WIDER exposure latitude

Double or half the mAs for every 5cm of part thickness

ADVANTAGES:
• Reduction in patient dose
• Provides more information within the image
• Increased consistency in density and contrast
• Lengthens exposure latitude
• Reduces x-ray tube wear
• Allows for shorter exposure times, thus reduces patient motion
• Easier to memorize

DISADVANTAGES:
• Lower overall contrast when compared to variable kVp systems
• Perceived as less pleasing to the eye
• Higher optimal kVp results in more scatter
Images have more gray

Question 31

What are AEC charts?

Answer 31

• Appropriate kVp must be selected for the part.
• Proper cell configurations must be selected.
• Density control selections are also available, 2,1,0, -1,-2. These adjust the set point of radiation intensity needed to activate the system. (generally a decrease in mAs)