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Huda Facts > 3 Huda Facts Final.csv - Huda Facts Final.csv > Flashcards

3 Huda Facts Final.csv - Huda Facts Final.csv Flashcards

1
Q

Watt

A

Joule/Sec

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2
Q

Lead K-edge

A

88 kev

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3
Q

X-ray wavelength is on the order of:

A

an atom

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4
Q

MR RF wavelength is on the order of:

A

a patient

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5
Q

K shell to outer shell binding energy ratio

A

1000 to 1

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6
Q

Tungsten k-edge

A

70 kev

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7
Q

Extremity radiograph relies mostly of which kind of x-ray interaction with tissue:

A

PE effect due to high z of bone (prob of PE effect increases with z cubed)

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8
Q

KVP for extremity radiograph

A

60 KVP

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9
Q

KVP for abdomen radiogaph

A

80 KVP

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10
Q

KVP for chest radiograph

A

120 KVP

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11
Q

MA for chest radiograph

A

500-1000

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12
Q

MA for CT

A

500-1000

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13
Q

MA for Fluoro

A

5

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14
Q

MAS for a chest xray

A

1

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15
Q

MAS for an abdomen radiograph

A

20

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16
Q

Does energy get transferred with coherent scatter?

A

No

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17
Q

Another name for coherent scatter

A

Raleigh

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18
Q

What percentage of X-rays are absorbed by a patient

A

67%

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19
Q

What percentage of X-rays are scattered by a patient

A

23%

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20
Q

What percentage of X-rays penetrate the patient and hit the detector

A

1%

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21
Q

Which energy is most likely transmitted by an Ag k-edge filter in mammo (25kev k-edge)

A

24 kev

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22
Q

Xray energy where PE = compton in tissue

A

25 kev

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23
Q

What is the half value layer of TISSUE (not aluminum) for x-rays

A

3 cm

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24
Q

What interaction is most likely in a head CT?

A

Compton

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25
Q

Air Kerma for lateral skull radiograph

A

1 mGy

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26
Q

Air Kerma for frontal skull radiograph

A

2 Gy

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27
Q

Air Kerma at the image receptor for all radiographs

A

3 micro Gy

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28
Q

Air Kerma at the receptor is kept constant by the:

A

automatic exposure control (AEC)

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29
Q

Kerma Air Product for a radiograph is about:

A

1 G-square centimeters

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30
Q

KAP for a small bowel follow-through is about:

A

10 G-square centimeters

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31
Q

KAP for a TIPS is about:

A

100 G-sq cm

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32
Q

Air Kerma rate for fluoro

A

10 mGy/min

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33
Q

Cu filter is added for:

A

pediatric radiography

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34
Q

What percentage increased in KAP if a patient gets fatter by 3 cm?

A

100% bc 3 cm of human tissue is one half value layer for radiographs

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35
Q

Which x-ray tube parameter is always increased in fat patients?

A

KVP (not mas)

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36
Q

Skin erythema is technically possible starting at what threshold air kerma?

A

2 Gy

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37
Q

Cataracts are technically possible starting at what threshold air kerma?

A

0.5 Gy

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38
Q

Average glandular dose for a single mammo?

A

3 mGy per view

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39
Q

Dose to the embryo from one abdominal radiograph?

A

1 mGy

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40
Q

Dose to the embryo from one abd/pel CT?

A

10 mGy

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41
Q

Which has highest linear energy transfer among x-rays, gamma rays, and beta particles?

A

All the same.

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42
Q

Effective dose for chest CT, abdomen CT, and pelvis CT?

A

All about 3-5 mSv

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43
Q

Effective dose for head CT?

A

About 2 mSv

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44
Q

Range and examples for very low dose exam?

A

less than 0.1 mSv - examples are extremity radiograph, chest radiograph, and skull radiograph

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45
Q

Range and examples for low dose exam?

A

between 0.1 and 1 mSv. Examples are lateral spine radiograph, abdominal radiograph, and extremity CT.

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46
Q

Range and examples for moderate dose exams?

A

Between 1 and 10 mSv. Examples are CT chest, CT abdomen, CT pelvis, small bowel follow through, and MDP bone scan.

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47
Q

Range and examples for high dose exams?

A

Above 10 mSV. Examples are TIPS, FDG-PET, and triple phase liver protocol CT.

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48
Q

Ubiquitous background radiation per year in the US?

A

1 mSV

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49
Q

Background radiation in the US due to Radon?

A

2 mSV

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50
Q

Average amount of radiation received by a NM tech per year?

A

3 mSv

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51
Q

Average amount of radiation received by both IR fellows and commercial airline pilots every year?

A

5 mSv

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52
Q

Cosmic radiation is higher where?

A

High altitudes

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53
Q

What is the scatter to primary ratio in abdominal x-rays?

A

5 to 1

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54
Q

Name 3 times when you DONT use a grid?

A

peds radiograph, extremity radiopgraphy, and mag mammo

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55
Q

Standard grid ratio for radiography

A

10 to 1

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56
Q

What do the numbers in the grid stand for?

A

first number is height of the septa. Second number is the space BETWEEN the septa.

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57
Q

What percentage of the primary transmission makes it through a grid?

A

70%

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58
Q

What percentage of scatter makes it through a grid?

A

10%

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59
Q

At which patient thickness do you have to start using a grid (in peds)?

A

12 cm

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60
Q

How much more radiation is needed to expose a traditional film without the screen?

A

50 x more

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61
Q

What makes a film “faster?”

A

thicker crystal with increased sensitivity (also increased blur from light dispersion)

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62
Q

Scintillator for FPD

A

CsI

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63
Q

Rank scintillator types by patient dose

A

CsI (lowest), BaFBr (medium), Se (highest)

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64
Q

Rank scintillator types by image sharpness

A

BaFBr (lowest), CsI (moderate), Se (best)

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65
Q

How many shades of gray does one byte code for?

A

256 (2 to the 8th power)

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66
Q

What are the only two imaging modalities that make use of only 1 byte (8bits = 256 shades of gray) per pixel?

A

NM and US (shitty images)

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67
Q

All of modalities make use of 2 bytes (16 bits = 512 shades of gray) per pixel

A

radiography, mammo, CT etc.

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68
Q

How big is a chest Xray file?

A

10 MB

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69
Q

How big is a mammo image file

A

15 MB

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70
Q

How big is a CT image (one slice) image file?

A

0.5 MB

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71
Q

How many pixels do you need on a monitor to read mammo?

A

5 MP

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72
Q

How man pixels do you need on a monitor to read x-ray?

A

3 MP

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73
Q

How many pixels do you need on a monitor to read CT?

A

2 MP

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74
Q

Who monitors monitors?

A

Society for Motion Picture and Television Engineers

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75
Q

Does analog or digital radiography have more quantum mottle?

A

same

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76
Q

How many line pairs can you see if the sampling frequency is 1/6

A
  1. Sampling frequency of 1/6 means 6 pixels for mm. If you divide pixels per mm, you get the number of line pairs visible.
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77
Q

What is the y axis of a ROC

A

Sensitivity or true positives

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78
Q

What is the x axis of a ROC

A

1-specificity or false positives

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79
Q

What is the relationship between geometric magnification and motion blur?

A

independent

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80
Q

Rank human cells, bacteria, and viruses in order of least to most susceptible to radiation?

A

human cells most then bacteria then viruses. Viruses are super resistant to radiation.

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81
Q

What is the latency period for the onset of radiation induced leukemia?

A

Years

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82
Q

What is the latency period for the onset of radiation induced solid cancer?

A

Decades

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83
Q

What is the background incidence of cancer in the US without additional exposure to radiation from medical exams?

A

40% of Americans get cancer

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84
Q

What is the risk of a 25 year old getting radiation induced cancer from 10 mSV of radiation?

A

0.10%

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85
Q

Has there been a study of human offspring having genetic effects of radiation?

A

No. Only animals. not even A bomb survivors.

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86
Q

What percent of human births have a genetic defect?

A

4%

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87
Q

What is the doubling dose for genetic defects?

A

1Gy (rate goes from 4% of births to 8%)

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88
Q

Deterministic effects for an embryo are VERY unlikely below what amount of radiation?

A

100 mGy

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89
Q

What is the rate of pediatric cancer in the US?

A

1 in 500

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90
Q

What is the doubling dose for pediatric cancers?

A

25 mGy. Rate goes from 1 in 500 to 2 in 500.

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91
Q

What is the downside to the ionization chamber method of detecting radiation?

A

Accurate but insensitive (needs billions of photons)

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92
Q

Ring radiation detector is what?

A

Thermoluminescent dosimeter (LiF)

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93
Q

Who regulates what radiology equipment can be sold in the US?

A

FDA

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94
Q

Who regulates dose limits for radiology equipment?

A

States

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95
Q

Regulatory dose limits exclude:

A

Medical exposures

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96
Q

Regulatory effective dose limits for radiation workers tries to reduce stochastic or deterministic risk?

A

Stochastic (cancer)

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97
Q

Eye dose limit

A

150 msv/year

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98
Q

Extremity limit

A

500 msv/year

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99
Q

Public dose limit

A

1 msv/year

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100
Q

Fetal dose limit per month

A

0.5 msv/month

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101
Q

Fetal dose limit for whole pregnancy

A

5 Msv after declaring

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102
Q

Who regulates radiopharmaceuticals?

A

NRC or agreement states

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103
Q

State regulation for required lead thickness in apron?

A

0.25 mm lead

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104
Q

How thick is lead usually in apron?

A

0.5 mm

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105
Q

How much does 0.5 mm of lead attenuate?

A

90%

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106
Q

Which tech gets the most annual radiation?

A

NM

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107
Q

Room shielding design?

A

2mm Pb thickness in the wall usually 2 meters high starting at the floor

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108
Q

Scattered x-ray intensity at 1 meter from the patient

A

1000 x less

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109
Q

What is the average monthly badge reading for radiology residents?

A

< 0.1 mSv per month

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110
Q

What does .DAM refer to?

A

Initiative to reduce dose called: “dont order tests that don’t affect management”

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111
Q

What is the dose limits for a medical imaging exam?

A

There are no dose limits

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112
Q

Average T1 time for human tissue?

A

~500 ms

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113
Q

Average T2 time for human tissue?

A

~50 ms

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114
Q

Average T2* time for human tissue?

A

~5 ms

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115
Q

Which water molecules have longer T1 time in human tissue?

A

Water in solids and free water - both T1 dark.

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116
Q

Which water molecules have shorter T1 time in human tissue?

A

Water that is structured such as proteinaceous water.

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117
Q

Larmor frequency at 1 T

A

42 MHz

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118
Q

What happens to T1 when spin-lattice interactions are increased?

A

Reduced

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119
Q

Does T1 change with different flip angles?

A

No, they are independent

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120
Q

What kinds of nuclei are used in MRI or NMR?

A

Those with odd mass numbers.

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121
Q

How are T1 and Bo related?

A

If you double Bo, T1 increases by root 2.

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122
Q

How are T2 and Bo related?

A

Not related.

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123
Q

What is the likely T2 value for protons in bone?

A

Very short. (dark)

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124
Q

Can T1 be less than T2 for a given tissue?

A

No. It’s impossible.

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125
Q

What are the units of magnetic field gradients?

A

Tesla per meter

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126
Q

In a 128 x 256 MRI grid, how many phase encoding steps?

A

128

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127
Q

In a 128 x 256 MRI grid, what does the 256 refer to?

A

Number of times an individual echo is parsed up or “sampled” by the receiver coil. This is the number of pixels in the frequency encoding direction.

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128
Q

Center of an MRI image shows?

A

Low spatial frequency. (contrast)

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129
Q

Periphery of an MRI image shows?

A

High spatial frequency. (resolution)

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130
Q

How does K space matrix size compare to MR image matrix size?

A

Same.

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131
Q

What will most likely reduce T1 weighting in a spin echo image?

A

Increasing TR.

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132
Q

What will most likely reduce T2 signal in a spin echo image?

A

Decreasing TE.

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133
Q

How does SNR increase with every additional NEX?

A

by root 2

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134
Q

What is the upside to GRE?

A

fast. Short TR.

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135
Q

What is the downside to GRE?

A

Worse SNR because signal is degraded by T2* effects, which remain present due to lack of 180 refocusing pulse.

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136
Q

STIR TI is about?

A

150ms

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137
Q

FLAIR TI is about?

A

2400

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138
Q

What kind of MRI sequence will produce the strongest echo?

A

SE>GE and shortest TE possible to reduce dephasing.

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139
Q

How many pixels would most likely be in a single echo within 128 x 196 SE image?

A
  1. For any given echo (and therefore a single line of K space), the number of pixels is determined by the numbers of samples taken - i.e., the number of data points along the frequency encoding direction.
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140
Q

Iron based MR contrast agents are?

A

supra-paramagnetic

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141
Q

How does heat dissipate between the focal spot and the anode body?

A

Conduction

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142
Q

How does heat dissipate between the anode body and the tube housing?

A

Radiation

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143
Q

How does heat dissipate between the tube housing and the atmosphere?

A

Convection

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144
Q

What is the usual anode angle?

A

~15 degrees.

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145
Q

Three ways to decrease heel effect?

A

Increase anode angle, decrease FOV AKA cassette size, increase SID.

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146
Q

Why use a large focal spot of 1.2 mm in PA and lateral chest XR?

A

Increasing focal spot size allows for more power and therefore quicker acquisition which is important to reduce respiratory motion.

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147
Q

What increases when KVP increases?

A

Both scatter and penetration.

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148
Q

If you increase mAs by 2 how much do you decrease mottle?

A

root 2

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149
Q

In fluoro what is the typical SID?

A

100 cm

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150
Q

Why keep the II or FPD close to the patient?

A

To reduce dose AND to reduce variable geometric magnification in the patient.

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151
Q

Typical SID for PA and lateral CXR?

A

72 inches

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152
Q

Use a grid in portable CXR?

A

no

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153
Q

Use a grid in portable abdominal XR?

A

yes. Reduce grid ratio from 10:1 to 5:1.

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154
Q

What is the problem in a CXR obtained at an exposure index of 100?

A

Way too much mottle. Huda would be furious that yo missed his lung nodule because your contrast to noise ratio would be lower. Not that contrast would not change; only mottle.

155
Q

Why do we see mach band artifact?

A

Lateral inhibition of the retina.

156
Q

If you see an XR and there are parts with fine exposure and parts with shitty exposure, whats the problem?

A

Faulty grid.

157
Q

Tube current in contact mammo?

A

100 MA.

158
Q

Tube current in mag mammo?

A

25 MA.

159
Q

mAs for contact mammo?

A

100 mAs

160
Q

mAs for mag mammo?

A

75 mAs.

161
Q

To change contrast in mammo is it effective to change KVP?

A

Not really. Better to change your target/filter.

162
Q

How does breast compression affect X-ray penetration?

A

Increases penetration because breast tissues is spread apart.

163
Q

Higher/lower/or comparable radiation in digital mammo versus screen film?

A

Comprable.

164
Q

Higher/lower/or comprable radiation in BTS versus FF mammo?

A

Comprable.

165
Q

What should the luminance be for a mammo monitor?

A

600 cd/ sq meter

166
Q

What is the problem with increasing SID to reduce geometric blur?

A

Takes longer resulting in motion artifact.

167
Q

What is the half value layer of normal breast tissue at mammo level xrays?

A

1 cm (compared to 3 cm for diagnostic radiography)

168
Q

What is the HVL of aluminum for mammo?

A

0.5 mm Al (compared to 3 mm Al for diagnostic radiography)

169
Q

What is the angular movement and number of images in BTS?

A

15 degrees, 15 images.

170
Q

What improves in BTS compared to FFDM?

A

Contrast. Resolution and dose DO NOT CHANGE.

171
Q

What are the only machines in radiology that are not regulated at the state level after they have been sold?

A

Mammo machines continue to be regulated at the federal level.

172
Q

What is the MQSA regulation for resolution for SF mammo?

A

12 lp/mm

173
Q

MQSA phantom specs?

A

4.2 cm breast, 50% glandularity.

174
Q

Use a grid in fluoro?

A

yes

175
Q

Grid ratio in fluoro?

A

10:1 (same as XR)

176
Q

In fluoro, what is the temporal resolution equal to?

A

The time for one frame to be acquired. (~33ms)

177
Q

What are the two advantages of pulsed fluoro?

A

reduces motion blur and increases contrast

178
Q

What does the FDA require on all digital fluoro machines?

A

last image hold

179
Q

Detector element for image intensifier (II)?

A

CsI

180
Q

How will replacing analog with digital fluoroscopy (alone) affect patient dose?

A

No change.

181
Q

What is different about GU fluoro machine compared to GI fluoro machine?

A

GU has the detector under the table.

182
Q

What is your KVP for iodine studies in fluoro?

A

70kvp

183
Q

What is your KVP for barium studies in fluoro?

A

110 kip

184
Q

Does the tube current change between iodine and barium studies in fluoro?

A

no. both 5 ma.

185
Q

When does the alarm go off in fluoro?

A

at 5 min.

186
Q

When you electronically mag something, what increases?

A

spatial resolution.

187
Q

When is the automatic brightness control (ABC) in effect?

A

Electronic mag modes ONLY

188
Q

What happens to AK with electronic mag?

A

Increases

189
Q

What happens with KAP with electronic mag?

A

Unchanged.

190
Q

What happens with AK with collimation?

A

Unchanged.

191
Q

What happens with KAP with collimation?

A

Decreases.

192
Q

In fluoro, what increases when collimation increases?

A

Contrast

193
Q

How many dose rate control buttons are there on a fluoro machine?

A

3

194
Q

How many photospot images equals the dose of 1 minute of fluoro?

A

10

195
Q

What is the number of images acquired at the 5 minute warning?

A

5000 (1000 per minute)

196
Q

Why do fluoro images look shitty?

A

Lots of mottle bc low MA (5 ma compared to 500-1000 for xr and IR)

197
Q

What is the spatial resolution of the II WITHOUT THE TV?

A

5 lp/mm (better than digital chest). The TV is the limiting factor.

198
Q

Name four types of artifacts that occur when using an II?

A

vignetting, s-distortion, image saturation, and pincushion.

199
Q

What are two requirements of High Level Control?

A

Audible and visual indicators

200
Q

Is there automatic brightness control (ABC) on flat panel detectors (FPD?)

A

No. Electronic mag does not require an increase in AK!

201
Q

Do you get saturation artifact with FPD?

A

No.

202
Q

Do you get image lag in FPD?

A

Yes.

203
Q

When you take a photo spot as opposed to a fluoro image, why does the image quality improve?

A

Less mottle. Higher mas.

204
Q

DSA tube current?

A

500 ma (approximately the same as XR, much higher than 5 ma in fluoro)

205
Q

What is the usual SID for angioraphy? What does this require for short operators?

A

100 cm (step stool)

206
Q

In fluoro/angio, does an air gap increase or decrease OPERATOR dose?

A

Increases. This is why you keep the II and FPD right next to the patient.

207
Q

What is the fraction of total KAP attributable to fluoro time in IR?

A

Only 1/3. The rest is from diagnostic images.

208
Q

How big is the spacer cone under the C arm that prevents SOD from getting too small?

A

Approximately 30 cm.

209
Q

Which action is the most helpful for reducing operator dose in IR?

A

shielding. way more effective than decreasing time or or increasing distance.

210
Q

By how much would effective dose go up in Pb aprons were not used in IR?

A

> 1000 x

211
Q

How many kinds of coils are there in an MRI magnet?

A
  1. Superconducting coil that creates the main magnetic field. Gradient coils for localization. Transmit/receive RF coils or excitation and FID signal collection.
212
Q

When you apply the slice select gradient, is the magnetic field higher at the head or feet?

A

feet

213
Q

Which MRI image acquisition requires the best field uniformity?

A

MRS

214
Q

What are two types of gradient coils?

A

Saddle and Helmholtz

215
Q

What is a quadrature coil?

A

A type of RF coil.

216
Q

Contrast enhanced MRA is what type of sequence?

A

3D GRE

217
Q

What are three factors that decrease signal in TOF?

A

turbulence, slow flow, and in plane flow.

218
Q

What is the net phase when a bipolar gradient is applied to stationary tissue and what sequence does this occur in?

A

No signal. Phase contrast imaging.

219
Q

What should be done to maximize tissue saturation in TOF MRA?

A

Decrease TR.

220
Q

What are the 3 types of images acquired from a phase contrast technique?

A

Phase, MIPS, and Magnitude

221
Q

In DWI the dephasing and rephasing gradients occur when?

A

On either side of the 180 degree refocussing pulse.

222
Q

Which MRI sequence is the fastest? FSE, GRE, or EPI?

A

EPI.

223
Q

What is the weighting of an EPI image?

A

Mostly T2* (no refocusing 180 pulse)

224
Q

About how long does it take to acquire images of the head (10 slices) using EPI?

A

1 second. Approximately 10 slice per second.

225
Q

Approximate spatial resolution of MRI?

A

0.3 lp/mm

226
Q

Approximate spatial resolution of CT?

A

0.7 lp/mm

227
Q

Approximate spatial resolution of DSA?

A

3 lp/mm

228
Q

How much would tripling each voxel dimension increase SNR?

A

x 27

229
Q

When in increase your receiver bandwidth what are you actually doing?

A

Increasing readout (frequency-encoded) gradient. This will decrease SNR.

230
Q

When B ranges between 1 and 1.1 T what is the likely receiver bandwidth?

A

4 MHZ because the Larmor Frequency of 1 T is 40 MHZ

231
Q

What does increasing the readout bandwidth decrease?

A

chemical shift AND susceptibility

232
Q

Using a multichannel receiver coil will have what effect on acquisition time?

A

Decreases it. Makes the scan faster.

233
Q

What are two effects of increasing the main magnetic field Bo?

A

Increased SNR. Increased T1 for all tissues. T2 is independent of Bo.

234
Q

How to fix Gibbs artifact?

A

Increase the MATRIX SIZE.

235
Q

Most common patient safety issue in MRI?

A

Burns. These constitute 70% of FDA reports.

236
Q

Which coil uses the most power in MRI?

A

Body. Biggest.

237
Q

What is the limit for whole body heating in normal mode for MRI?

A

Up to 0.5 degrees C

238
Q

What is the limit for whole body heating in 1st level (supervised) mode?

A

Up to 1 degree C

239
Q

What is the limit for whole body heating in 2nd level (IRB approved mode?

A

No limit. Above 1 degree C.

240
Q

Noise from gradient coils should be kept below which level?

A

100 dB

241
Q

What zone do you code a patient in?

A

Zone 2. Remove the patient from the scanner all the way to Zone 2.

242
Q

What shape is the MR safe sign?

A

Square.

243
Q

What shape is the MR conditional sign?

A

Triangle.

244
Q

What shape it the MR not safe sign?

A

Circle

245
Q

What should MRI patients be advised to wear to protect their ears?

A

Both ear plugs and ear protectors.

246
Q

Fan v. cone angle of a CT beam

A

Fan angle is in the axial plane of the patient. Cone angle extends along the z axis of the patient.

247
Q

1 line of a sonogram is called?

A

A projection

248
Q

1 line of a projection is called?

A

A ray

249
Q

Does a smoothing filter affect contrast?

A

Technically no. It just decreases noise and therefore increases CNR.

250
Q

Does an edge enhancing filter affect contrast?

A

Technically no. It increases SR but unfortunately also increases noise.

251
Q

What are two examples of edge enhancing filters?

A

Bone and lung kernels.

252
Q

Which is better: statistical iterative reconstruction of model-based iterative reconstruction?

A

Model-based.

253
Q

What is the equation for Hounsfield Units

A

1000 x (Attenuation in question - Attenuation of Water) / Attenuation of Water

254
Q

A 10 HU changes represents what change in attenuation?

A

1%

255
Q

If you increase KVP does a calcium kidney stone attenuate more or less photons?

A

Less

256
Q

If you increase KVP does a uric acid stone attenuate more or less photons?

A

More

257
Q

Are CT x-ray beam filtered?

A

Highly filtered to reduce beam hardening artifact

258
Q

What is a CT detector made out of?

A

CsI

259
Q

What does detector offset refer to in CT?

A

at 180 degrees the projection will be slightly different. this improves spatial resolution.

260
Q

Typical thickness of a CT slice acquisition?

A

0.5 mm

261
Q

Typical thickness of a CT slice on the monitor?

A

4-5 mm

262
Q

Is the anode capacity for heat higher or lower than traditional XR?

A

higher

263
Q

In CT xray tube output will increase more by increasing KVP or MAS?

A

KVP. Increase of 15% KVP will double the output. MAS rises linearly.

264
Q

What are the 2 sizes of phantoms in CT for measuring CTDI vol?

A

16 cm and 32 cm.

265
Q

What size CT phantom for head?

A

16 cm

266
Q

What size CT phantom for body?

A

32 cm

267
Q

What size CT phantom for the neck?

A

Variable.

268
Q

What size CT phantom for peds?

A

Variable.

269
Q

What are the units for KAP in fluoro?

A

G x sq cm

270
Q

What are the units for CTDI in CT?

A

G x cm

271
Q

Is KVP or MA adjusted by the AEC in CT?

A

Just the MA.

272
Q

What is the average KVP in CT for a fat patient?

A

140

273
Q

What is the average KVP in CT for a not fat patient?

A

120

274
Q

What is the average KVP for CT with contrast studies using iodine?

A

80

275
Q

What is the ACR dose limit for a head CT? What is the average dose for a head CT?

A

CTDIvol 80mGy is the limit. CTDIvol 60mGy is the average.

276
Q

How does CT fluoro work?

A

continuous tube rotation.

277
Q

How many images per second acquired in CT fluoro?

A

6

278
Q

Is KVP or MAS or both reduced in CT fluoro?

A

Only MAS - about 20% of the diagnostic dose.

279
Q

What is the most likely CTDIvol for an infant head CT?

A

Half of an adult = 30 mGy.

280
Q

What is effective MAS?

A

MAS/pitch

281
Q

What is the best possible temporal resolution of a CT scan?

A

0.5 x the rotation time.

282
Q

How long does it take a modern CT to rotate one time?

A

300ms

283
Q

What is the best possible temporal resolution for a dual source (not necessarily dual energy) CT scanner?

A

0.25 x rotation time = 75 ms.

284
Q

What happens to CT noise with MAS and slice thickness are both doubled?

A

Halved bc mas decreases noise linearly and slice thickness increases noise by square root.

285
Q

Name four things that affect SR in CT

A

Focal spot, detector size, reconstruction filter choice, and field of view.

286
Q

Ring artifacts in CT imply which generation scanner?

A

3rd

287
Q

Two ways to fix streak artifact from metallic implant in CT?

A

Use iterative reconstruction. Increase KVP.

288
Q

When is cone beam CT used?

A

dentists

289
Q

What is a Bushberg / Defrise Phantom?

A

Google it. Know it.

290
Q

What causes aliasing in all modalities: CT, MRI, and US?

A

Undersampling.

291
Q

In IR and fluoro where is the AK measured?

A

15 cm from the patient’s isocenter closer to the source. This spot is called the Interventional Reference Point (IRP)

292
Q

Helpful approximation: what should you assume the peak skin dose is equal to in fluoro/IR?

A

Air Kerma at the Interventional Reference Point (IRP)

293
Q

What is the frequency of “serious skin burns” in IR?

A

1 out of 10,000

294
Q

At what peak skin dose, does the Joint Commission visit for a sentinel event?

A

15 G

295
Q

What is the most likely peak skin dose during an IR procedure

A

1 G

296
Q

What is the patient peak skin dose limit in IR?

A

No limit.

297
Q

What is considered a “very low dose” radiology procedure. Name 3 examples.

A

< 0.1 mSv. Skull, chest, and extremity XR.

298
Q

What is considered a “low dose” radiology procedure. Name 3 examples.

A

Between 0.1 and 1 mSv. Abdominal and spine XR. Extremity CT.

299
Q

What is considered a “moderate dose” radiology procedure. Name 3 examples.

A

Between 1 and 10 mSv. Chest CT, Abdominal CT, Small bowel follow-through fluoro, MDP bone scan.

300
Q

What is considered a “high dose” radiology procedure. Name 3 examples.

A

Greater than 10 mSV. TIPS, FDG-PET, triple phase liver CT.

301
Q

Name 3 things that are considered when converting the CT DLP into an effective dose (mSV)

A

Body region, physical size of the organs involved, patient age.

302
Q

What is the approximate dose the embryo from a CT abd/pelvis on a pregnant woman?

A

10-20 mSV. For context, there is NO risk of deterministic effects on the fetus before a cumulative dose of 100mSV; however, there is an increased stochastic risk to the fetus starting around 25 msV.

303
Q

Average CTDIvol and effective dose for a head CT?

A

60mGy for CTDI. 2mSv for effective dose.

304
Q

Average CTDIvol and effective dose for a chest CT

A

10mGy for CTDI. 6mSv for effective dose.

305
Q

Which of the following has the lowest dose? Head ct, chest ct, abdomen ct, or pelvis ct?

A

head ct. Only 2 mSv. The rest are about 5 mSv.

306
Q

Approximate fetal dose for a single abdominal radiograph?

A

1 mGy (no deterministic effects below 100 mGy)

307
Q

Compared to a 25 year-old how much more/less stochastic risk does an infant have for the same amount of radiation?

A

3 x more stochastic risk

308
Q

Compared to a 25 year-old how much more/less stochastic risk does an old person have for the same amount of radiation?

A

3 x less stochastic risk

309
Q

Screening mammo is in which dose category? Very low, low, moderate, or high?

A

Low (0.1 to 1 mSv)

310
Q

About how much dose to the fetus per minute when performing fluoro on mother?

A

2 mGy/min

311
Q

What is the stochastic risk of cancer from 10mSV of effective dose in a 25 year old?

A

0.1 percent. Risk of cancer rises from 40% to 40.1%.

312
Q

Creation method for radionuclides that decay via B-?

A

Either reactors or fission

313
Q

Difference between reactor and fission products?

A

Reactor products are NOT carrier free. Fission products are carrier free.

314
Q

Do cyclotrons add charge or subtract charge?

A

Add. Products have an extra proton. They get stable by releasing a positron or capturing an electron.

315
Q

1 mCi is how many Bq?

A

37 MBq

316
Q

Half life activity equation using decay constant

A

T(1/2) x 0.69 = decay constant

317
Q

Long parent half life and short daughter half life is called what?

A

Secular equilibrium

318
Q

Equilibrium occurs after how many half lives?

A

4

319
Q

How would a radionuclide produced in a cyclotron most likely decay

A

Beta positive decay

320
Q

How would a radionuclide made in a reactor likely decay?

A

Beta negative decay.

321
Q

What is the energy resolution for I123 if the photo peak width is 16 kev

A

10%

322
Q

Who regulates administered radionuclides?

A

NRS or agreement states

323
Q

What is the most likely photo peak width for Tc 99m gamma rays?

A

14 kev

324
Q

What is another name for a low energy collimator?

A

Foil collimator. Used for Tc 99m as well as I 123.

325
Q

What goes down far from the NM collimator? Spatial resolution, SNR, or Contrast?

A

Spatial Resolution

326
Q

How many counts are acquired in uniformity correction flood images?

A

100 million (happens quarterly and typically scheduled for overnight)

327
Q

What two variables have the most impact on the quality of a nuclear medicine study?

A

collimator selection and # of counts

328
Q

Which type of collimator will result in the WORST spatial resolution?

A

Diverging.

329
Q

What kind of collimator do you use for a MDP bone scan planar acquisition?

A

LEHR

330
Q

About how many minutes does it take to acquire ALL of the photons from a MDP bone scan?

A

15m

331
Q

Name one type of iterative reconstruction?

A

OSEM (Ordered subset expectation maximization)

332
Q

In NM what is a high pass filter?

A

Same thing as high spatial frequency filter = high resolution filter. SR increases. Sensitivity decreases.

333
Q

In MRI what part of k space does a high pass filter remove?

A

Center of K space. You still have good spatial resolution but you lose contrast.

334
Q

In MRI what part of k space does a low pass filter remove?

A

Periphery. You lose spatial resolution, but you still have contrast.

335
Q

In SPECT what determines resolution perfomance?

A

lead collimator height and distance between collimators

336
Q

Approximate pixel size (mm) for chest X-ray?

A

0.1 mm

337
Q

Approximate pixel size (mm) for NM spect?

A

2 mm

338
Q

What accounts for improved image quality in PET compared to SPECT?

A

More counts. Less mottle.

339
Q

Two ways to know you are looking at an attenuation correction image in PET?

A

bright lungs and NO dark line around the periphery of the body.

340
Q

Two ways to know you are looking at a non-attenuation correction image in PET?

A

dark lungs and dark periphery of the body.

341
Q

What do you use Phosphorus 32 for?

A

Treating polycythemia vera. Pure alpha emitter.

342
Q

What are the only two imaging modalities in which you code 1 pixel with 1 byte

A

ultrasound and nm. the rest of the modalities code 1 pixel with 2 bytes (=16 bits)

343
Q

What is another name for the gamma camera?

A

anger camera

344
Q

What is mistuning or detuning in NM?

A

When the energy window is mis-aligned so that the photons you are interested in (e.g. 140 for Tc99m study) are not being counted.

345
Q

What is the photo peak for Co 57 and when is it used?

A

120 kev. for daily uniformity checks on anger cameras.

346
Q

What is the degree of variability allowed for gamma cameras during daily uniformity testing with Co 57?

A

2-3 percent

347
Q

Where is SR and linearity measured during weekly checks on anger cameras?

A

Right up against the anger/gamma camera. Because spatial resolution falls off rapidly with distance from the camera, these weekly checks always overestimate the system SR.

348
Q

Without doing calculations, what is the approximate wavelength of a ultrasound wave using a 15 MHz transducer?

A

~0.1 mm

349
Q

Speed of sound in bone

A

4000 m/s

350
Q

What kind of reflection is useful in diagnostic ultrasound?

A

specular. non-specular aka diffuse is garbage.

351
Q

When does scatter happen in ultrasound?

A

when the interface being interrogated by the ultrasound beam is much smaller than the beam wavelength.

352
Q

In ultrasound how much attenuation does a 10 dB drop result in?

A

10 percent.

353
Q

In ultrasound how much attenuation does a 20 dB drop result in?

A

1%

354
Q

What is the approximate mHz of an abdominal ultrasound transducer?

A

3 MHZ

355
Q

What is the approximate mHz of a breast transducer?

A

10-15 MHZ

356
Q

Name three high ultrasound attenuators

A

Air, lung, bone

357
Q

In human tissue, what is the change in decibel with depth?

A

0.5 db/cm /mHZ

358
Q

What is the unit of acoustic impedence?

A

Rayl

359
Q

Transducer thickness is equal to?

A

1/2 wavelength

360
Q

What has the highest acoustic impedence?

A

PZT (what the transducer crystals are made out of) is higher than bone.

361
Q

Does lung attenuate ultrasound beams a lot or a little?

A

a lot despite having low impedence.

362
Q

Roughly how many PZT elements are there in a clinical ultrasound probe?

A

About 100

363
Q

What’s the most likely number of lines in a single ultrasound image?

A

About 100

364
Q

How are elements fired in a phased array ultrasound transducer?

A

All at once

365
Q

Ultrasound is:

A

“always focused”

366
Q

What is the reduction in US frame rate from using 5 focal zones?

A

Five times slower

367
Q

What is the advantage of a 1.5D ultrasound array?

A

Better elevational resolution

368
Q

What feature of phased array probes gives you better lateral resolution?

A

The ability to set multiple focal zones

369
Q

What do phased arrays vary to steer and focus the ultrasound beam?

A

Time delays

370
Q

3 ways to increase line density?

A

Decrease the frame rate, field of view, or depth.

371
Q

What is the product of lines per frame and image frame rate?

A

Pulse repetition period

372
Q

On an ultrasound machine, does gain affect depth?

A

No

373
Q

To avoid aliasing in ultrasound the PRF must be at least what?

A

2x the doppler shift

374
Q

A fetus kicking during an ultrasound exam will cause what kind of artifact?

A

Flash artifact. Apparently this can be corrected for using something called a “wall filter”

375
Q

What is “continuous doppler?”

A

The machine use you during a code to listen for someone’s pulse. No images provided, only audible response to blood flow.

376
Q

How does increasing the spatial pulse length affect axial resolution?

A

Inversely related. High SPL, worse axial resolution.

377
Q

Axial resolution is about what?

A

1/2 the SPL

378
Q

Is lateral resolution better than worse than axial resolution in ultrasound?

A

4x worse than axial resolution regardless of transducer frequency.

379
Q

In ultrasound, does spatial compounding affect noise?

A

Yes, it decreases noise.

380
Q

In ultrasound, does spatial compounding affect contrast?

A

No.

381
Q

Which ultrasound resolution is changed by adjusting the frame rate? Axial, elevational, or lateral?

A

Lateral.

382
Q

Name three assumptions the ultrasound machine makes that accounts for artifacts?

A

Sound waves travel in straight lines. Only one reflection per beam. Speed of sound in tissue is uniform.

383
Q

In what category of dose does ERCP belong?

A

Moderate = between 1 and 10 mSv.

384
Q

Compare the receptor air kerma between a chest X-ray and a mammogram and explain why there is a difference?

A

3 microG for CXR. 100 microG for mammo. Need less mottle in mammo to detect subtle differences. Can tolerate higher mottle in xr.

Huda Facts (5 decks)

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