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Radiology Principles Class > Unit 2 Beam Restriction, Grids, & Filtration > Flashcards

Unit 2 Beam Restriction, Grids, & Filtration Flashcards

1
Q

Beam Restriction

A

-Limits the scatter that is produced inside the patient
-Reduces the size of the exposure area and volume of tissue being irradiated
-Reduces the # of Compton interactions that occur

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2
Q

Functions of collimator

A

-Reduces effects of off focal radiation
-Reduces Penumbra(image unsharpness)

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3
Q

What is Positive Beam Limitation (PBL)?
Why is it important?

A

• Automatically collimates the beam to the size of the IR
• ALARA: Beam size should never exceed size of IR

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4
Q

In what 2 instances should a Radiographer consider grid use?

A

-Body part over 10cm
-kVp above 70

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5
Q

T or F: Grid use decreases subject contrast

A

False, it increases

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6
Q

T or F: Grids reduce scatter that REACHES the IR

A

True

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7
Q

Collimation reduces the ________ of scatter of photons

A

Production

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8
Q

Why do parallel grids only work with long SID?

A

Because more of the beam is going straight up and down and less spread out

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9
Q

What kind of grid is used in moving systems?

A

Parallel grids

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10
Q

Focused Grid characteristics

A

• Grid strips align with divergent beam
• Grid Radius
• Focal Range: range of appropriate SID

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11
Q

What is a Potter-Bucky diaphragm? What are the 2 types of grid motion?

A

• Grid lines run longitudinally
• Designed to move during exposure

• Reciprocating
-Move back and forth
• Oscillating
-Circular motion

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12
Q

Which grid motion can withstand faster/shorter exposure times?

A

Oscillating

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13
Q

Grid Ratio

A

• Height of lead strips: width of interspace
• Higher ratio = Better Clean up

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14
Q

Grid Frequency

A

• # Lead strips per inch
• Higher frequency = thinner strips
• Digital systems require 178-200 lines/in

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15
Q

Does a higher or lower grid ratio absorb more scatter?

A

Higher

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16
Q

Higher grid frequency, the strips become _______

A

Thinner

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17
Q

________ grid frequency can show up as an artifact in x-ray images

A

Lower

18
Q

Digital systems require a GF of ____
Why?

A

178-200 lines/in;
because strips will show up in picture if not in this range

19
Q

Does Higher grid ratio mean higher or lower contrast?

A

Higher

20
Q

Lead Content

A

Total amount of lead in grams/cm

21
Q

Selectivity

A

% primary beam transmitted vs. % scatter transmitted

22
Q

What is Contrast Improvement Factor (K)? What is the typical range?

A

The ratio of Subject contrast obtained with the grid vs. without

1.5-3.5

23
Q

Pros of using grids

A

• Reduction of Scatter that reaches the IR
• Improved Subject contrast and visibility of detail

24
Q

Cons of using grids

A

• Reduction of IR Exposure
• Requires increase in mAs
• Increased patient dose
• Radiographer error

25
Q

Common Grid Ratios and their GCF

A

Grid GCF
Ratio
No grid —> 1
5:1 ———-> 2
6:1 ———-> 3
8:1 ———-> 4
10:1 ———-> 5
12:1 ———-> 5
16:1 ———-> 6

26
Q

No Grid to Grid Formula

A

GCF = mAs with Grid/mAs without Grid

If you’re going from higher grid ratio to no grid you divide, if you’re going from no grid to higher grid ratio you multiply

27
Q

Grid to grid formula

A

mAs 1 GCF 1
——- = ———
mAs 2 GCF 2

28
Q

Technologist ERROR can result in

A

Grid Cut Off

29
Q

Grid cut off

A

Absorption of the primary beam

30
Q

4 types of grid cut-offs

A

-Off-Level/Canting
-Off-Centering
-Off-Focal
-Upside Down

31
Q

Which of the 2 grid cut-offs cut off on ENTIRE IR

A

-Off-Level/Canting
-Off-Centering

32
Q

Which 2 grid cut-offs cut off on Periphery

A

-Off-Focal
-Upside Down

33
Q

What is the purpose of a filtration of the x-ray beam?

A

-Eliminates low energy photons from the beam
-Reduces patient dose
-Increases mean energy of the beam (Harder)
-Negligible(small/unimportant) impact on IR Exposure

34
Q

As filtration increases, the intensity(quantity) of the beam _________ and the quality ________

A

Decreases; Increases

35
Q

Half-Value Layer

A

The amount of absorbing material that will reduce the intensity of the beam by half

36
Q

Inherent Filtration

A

-0.5 mm Al/Eg

These make up the Inherent Filtration:
• Envelope
• Insulating Oil
• Port Window

37
Q

Added Filtration

A

-2.0 mm Al/Eg Mror

These make up the Added Filtration:
• Aluminum Sheet 1.0mm
• Mirror 1.0mm

38
Q

Total Filtration

A

2.5 mm Al/Eq

39
Q

Compensation Filter

A

Designed to compensate for varying thicknesses in tissue in order to even out the Exposure to the IR

40
Q

For a unit that operates over 70 kVp, what is the required minimum amount of filtration?

A

2.5 mm AI/eq

41
Q

Beam restriction devices

A

-Collimator
-Cones and Cylinders

Radiology Principles Class (10 decks)

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