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Physics > Basics 3 > Flashcards

Basics 3 Flashcards

1
Q

What is noise?

A

Any data that does not contribute to the image

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2
Q

What are 3 factors that affect scatter?

A
  1. KVP- Higher KVP means Compton Scatter predominates
  2. Thicker- Thicker Tissue= more Scatter
  3. Large FOV= More Scatter
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3
Q

How does Collimation affect noise?

A

Collimation decreases noise

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4
Q

What is the Grid Ratio?

A

Height of the Lead/Distance between lead bars

-Increased Grid Ratio means less scatter but more dose

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5
Q

What is the Bucky Factor?

A

Increase in Dose due to use a grid (due to the increased mA)

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6
Q

What is Grid Cutoff and how to you fix it?

A

Image becomes very noisy bc too many photons are blocked.

-Realign the Grid, this usually occurs bc the grid is aligned incorrectly.

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7
Q

Should you increase mA or kVp to decrease noise?

A

mA, because increasing kVp can also lead to more compton scatter

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8
Q

How can you decrease noise?

A
  1. Use a Grid (more Dose)
  2. Increase the mA
  3. Use an Air Gap
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9
Q

How does distance from the source affect image noise?

A

Increased distance between source and detector= increased noise
Inverse square law= Energy twice as far from the source is spread out over 4 times the area

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10
Q

What is spatial resolution?

A

The ability to tell two lines apart that are very close to each other.

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11
Q

What are the 3 types of unsharpness?

A
  1. Motion unsharpness (pt moves)
  2. System unsharpness (Detector issues)
  3. Geometric unsharpness (focal spot size and Source to object distance)
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12
Q

What limits spatial resolution in film, computed radiography and Digital radiography?

A
  • Film: Limited by Grain size
  • Computed Radiography: Limited by size of laser to read phosphor plate
  • Digital Radiography: Limited by size of thermoluminecient transitor
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13
Q

What is the equation for Magnification?

A

Source to image distance/Source to object distance

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14
Q

What is the difference between sharpness and resolution?

A
  • Sharpness: Ability to define an edge

- Resolution: Ability to tell 2 things apart

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15
Q

What is Modulation Transfer Function?

A

Output/Input

-It describes the resolution capabilities of the system

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16
Q

What is Detective quantum efficiency (DQE)?

A
  • Efficiency of the Detector in converting x ray signal to image
  • Estimates the require dose to create an optimal image
17
Q

How does DQE effect dose?

A
  • High DQE= Low Dose

- Low DQE= High Dose

18
Q

How does DQE relate to MTF?

A

Directly proportional

19
Q

How does DQE relate to SNR?

A

Inversely proportional

20
Q

How dose DQE relate to Spatial resolution?

A

Inversely proportional

21
Q

What is pixel pitch?

A

Distance from the center of one pixel to another pixel

-Decreased pixel pitch= better resolution

22
Q

What is the primary factor influencing imaging contrast in Film versus digital?

A
  • Film: KVP

- Digital: Look Up Table (LUT)

23
Q

WHat is window length and window width?

A
  • Length: Selects the Image Brightness

- Width: Selects the contrast

24
Q

What is the 30% rule?

A

-Need to increase the mAs by at least 30% to see a change in film density (blackness)

25
Q

How do you adjust the mA for fat people?

A

Double the mA for every 4 cm increase in distance

26
Q

How do you decrease Scatter?

A
  1. Collimate
  2. Compress the tissue (thinner tissue)
  3. Lower KVP
  4. Grid
  5. Air Gap
27
Q

How do you adjust technique for Cast?

A

Fiberglass: No Change
Plaster: Increase the mA by 2 or 3 times

28
Q

What are situations to increase the kVP?

A
  • Splenomegaly
  • Ascites
  • Sclerotic phase of pagets
29
Q

What are situations to decrease KVP?

A
  • Emphysema
  • Lytic phage of pagets
  • Osteoperosis
30
Q

How do you change technique for a sof ttissue neck radiograph?

A

Increase mAs

Physics (10 decks)

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