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Core > Physics: Rapid Review, Nuclear and MRI > Flashcards

Physics: Rapid Review, Nuclear and MRI Flashcards

1
Q

Isotope

A

Same number of protons

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2
Q

Isotone

A

Same number of neutrons

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3
Q

Isobar

A

Same mass number

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4
Q

Isomer

A

Same number of protons and neutrons, but different energies (e.g. Tc99 and Tc99M)

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5
Q

Effective half life

A

Effective half life = (1/physical half life) + (1/biological half life)

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6
Q

Physical half life of Tc99m

A

6 hours

Note: Turn the 9 upside down to get 6.

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7
Q

Tc99m energy

A

Low (140)

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8
Q

Physical half life of I-123

A

13 hours

Note: 123 is 13.

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9
Q

Physical half life of Xe-133

A

125 hours

Note: Biological half life is 30 sec (breathed out).

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10
Q

Physical half life of Thallium-201

A

73 hours

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11
Q

Physical half life of Indium-111

A

67 hours

Note: Indium wishes it was Ga-67.

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12
Q

Physical half life of Gallium-67

A

78 hours

Note: +1 to each digit.

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13
Q

Physical half life of I-131

A

8 days

Note: If you spill I-131 you’re fucked (for a week and a day).

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14
Q

Physical half life of F-18

A

110 min

Note: Formula 1 is fast (110 mph).

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15
Q

Physical half life of cobalt-57

A

270.9 days

Note: Almost a year (3/4 of a year). This is used for quality assurance (extrinsic field uniformity).

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16
Q

Physical half life of germanium-68

A

270 days

Note: This is used for PET quality assurance.

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17
Q

Physical half life of Gallium-68

A

68 minutes

Note: This is used for PET quality assurance.

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18
Q

Half life of strontium-89

A

50.5 days (14 days in bone)

Note: 2 weeks in bone, but ~2 months elsewhere.

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19
Q

Half life of samarium-153

A

46 hours

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20
Q

Half life of radium-223

A

11 days

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21
Q

Half life of Yttrium-90

A

64 hours

Note: Turn 9 upside down to get 6 (then times 10 because it’s therapeutic, so you should expect it to last longer than 6 hours).

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22
Q

Half life of rubidium-82

A

75 seconds

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23
Q

Half life of nitrogen-13

A

10 min

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24
Q

Energy of I-123

A

Low (159)

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25
Q

Energy of Xe-133

A

Low (81)

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26
Q

Energy of Thallium-201

A

Low (167 and 135)

Note: It is actually the Hg-201 daughter xrays that are images.

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27
Q

Energy of Indium-111

A

Medium (173 and 247)

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28
Q

Energy of Gallium-67

A
  • 93 (40%)
  • 184 (20%)
  • 300 (20%)
  • 393 (5%)

Note: 90, 180, 300, 400.

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29
Q

Energy of I-131

A

High (365)

Note: Days in a year.

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30
Q

Energy of F-18

A

High (511)

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31
Q

Energy of Cobalt-57

A

Low (122 and 136)

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32
Q

Energy of Germanium-68

A

High (511)

Note: This is actually the energy of its daughter product Gallium-68.

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33
Q

Beta minus decay causes…

A

Emission of a beta particle (electron)

Note: This is an isobaric transition.

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34
Q

Beta plus decay causes…

A

Emission of a positron

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35
Q

Electron capture causes…

A

An electron and proton to merge and become a neutron

Note: A gamma photon can also be produced if coupled with an isomeric transition.

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36
Q

Alpha decay causes…

A

Emission of an alpha particle (helium nucleus, 2 protons and 2 neutrons)

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37
Q

What type of atoms undergo beta minus decay?

A

Lots of neutrons and not enough protons

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38
Q

What type of atoms undergo beta plus decay?

A

Lots of protons and not enough neutrons

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39
Q

What type of atoms undergo electron capture?

A

Lots of protons and not enough neutrons

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40
Q

What type of atoms undergo alpha decay?

A

Heavy unstable atoms

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41
Q

Which type of collimator produces a fixed image size that is independent of image distance?

A

Parallel hole

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42
Q

Best collimator type for thryoid scintigraphy

A

Pinhole

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43
Q

How does a pinhole collimator affect the image?

A

Magnifies and inverts the image (the closer to the collimator, the more magnification)

Note: The farther from the detector, the less magnification (no magnification if equal distance between pt-collimator and collimator-detector).

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44
Q

What collimator should you use if you want to magnify without inverting the image?

A

Converging

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45
Q

As the pt gets farther from a converging collimator, magnification _______

A

Increases (and field of view decreases)

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46
Q

What collimator should you use if you want to take a large object and make a smaller image (e.g. lung scan with a mobile gamma camera)?

A

Diverging collimator

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47
Q

Using longer septa in a collimator…

A
  • Lowers sensitivity (increases noise)
  • Increases spatial resolution
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48
Q

Using thinner septa in a collimator…

A
  • Increases blur (increased penetration)
  • Increases sensitivity (more photons reach detector)
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49
Q

Wider collimator holes result in…

A
  • Higher sensitivity (more photons reach detector)
  • Lower spatial resolution
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50
Q

Frequency for nuclear quality assurance on constancy

A

Daily (using a reference source)

Note: Should be within 5% of computed activity.

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51
Q

Frequency for nuclear quality assurance on linearity

A

Quarterly (using a large activity of Tc-99m, about 200 mCi, and decaying it to less than the smallest activity you would measure for use)

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52
Q

Frequency for nuclear quality assurance on accuracy

A

Annually (using standard energy sources)

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53
Q

What are the standard energy sources used to check for nuclear imaging accuracy?

A
  • Co-57 (low energy)
  • Cs-137 (medium)
  • Co-60 (high energy)
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54
Q

Frequency for nuclear quality assurance on geometry

A

Once during installation and again any time you move the device (using different volumes of liquid Tc-99m)

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55
Q

Best detector to survey for low level radioactivity?

A

Geiger-Muller counter (very sensitive, but horrible for high radiation fields)

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56
Q

What types of radiation can be detected with a Geiger-Muller counter?

A

Ionizing radiation (alpha, beta, and gamma)

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57
Q

What type of detector should be used to survey high level radiation?

A

Ionization chamber (stable across a wide voltage range)

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58
Q

How should you wear a personal thermo-luminescent dosimeter?

A

Wear the ring on a finger with the label facing the palm (should be worn under gloves if using gloves)

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59
Q

What are the major types of survey meters?

A
  • Geiger-Muller counter
  • Ionizing chamber
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60
Q

What type of radioactivity detector should be used for “wipe test” or urine/blood samples?

A

Well counter

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61
Q

Where would you look up notices, instructions, and reports to workers for nuclear medicine?

A

10 code of federal regulations, part 19

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62
Q

Where would you look up standards for protection against radiation?

A

10 code of federal regulations, part 20

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63
Q

Where would you look up information about the medicinal use of by-product material?

A

10 code of federal regulations, part 35

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64
Q

What is considered a major spill for Tc-99m?

A

> 100 mCi

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65
Q

What is considered a major spill for Thallium-201

A

> 100 mCi

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66
Q

What is considered a major spill for Indium-111

A

> 10 mCi

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67
Q

What is considered a major spill for I-123?

A

> 10 mCi

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68
Q

What is considered a major spill for Ga-67?

A

> 10 mCi

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69
Q

What is considered a major spill for I-131?

A

> 1 mCi

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70
Q

What is the protocol for a major spill?

A
  • Clear area
  • Cover spill with absorbent paper (do NOT clean it up)
  • Clearly indicate boundaries of spill area (limit movement of contaminated persons)
  • Shield source if possible
  • Notify radiation safety officer immediately
  • Decontaminate persons
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71
Q

What is the annual radioactive dose limit to a member of the general public?

A

100 mrem

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72
Q

What is the radioactive dose limit for an unrestricted area?

A

2 mrem/hour

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73
Q

What is the definition of a restricted area in nuclear medicine?

A

Any area that receives a dose greater than 2 mrem/hour

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74
Q

Where should you place “radiation area” signage?

A

Anywhere that you could get 5 mrem (o.oo5 rem or 0.05 mSv) in 1 hour at 30 cm

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75
Q

Where should you place “high radiation area” signage?

A

Anywhere you could get 100 mrem/0.1 rem (1 mSv) in 1 hour at 30 cm

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76
Q

Where should you place “very high radiation area” signage?

A

Anywhere you could get 500 rads (5 gray) in 1 hour at 1 meter

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77
Q

What is the NRC occupational exposure dose limit for total body dose per year?

A

5000 mrem/5 rem (50 mSv)

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78
Q

What is the NRC occupational exposure dose limit for dose to the ocular lens per year?

A

15 rem (150 mSv)

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79
Q

What is the NRC occupational exposure dose limit for total equivalent organ dose?

A

50 rem (500 mSv)

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80
Q

What is the NRC occupational exposure dose limit for total dose to embryo-fetus over entire 9 months of pregnancy?

A

500 mrem/0.5 rem (5 mSv)

Note: If the fetus has already gotten 5 mSv at the time of pregnancy declaration you can get 0.5 mSv more for the remainder of the pregnancy.

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81
Q

1 rad = ? rem

A

1 rad = 1 rem

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82
Q

1 rem = ? Gy

A

1 rad/rem = 0.01 Gy

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83
Q

1 mSv = ? mrem = ? rem

A

1 mSv = 100 mrem = 0.1 rem

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84
Q

5 rem = ? mSv

A

5 rem = 50 mSv = 0.05 Sv

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85
Q

At what dose does a mistake become a reportable event in nuclear medicine?

A

Pt received at least 5 rem of whole body radioactive dose that they shouldnt have gotten

OR

Pt received at least 50 rem single organ dose that they shouldn’t have gotten

Note: If there was a mistake, but less than these limits it is considered a recordable event (only locally recorded for local institutional review)

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86
Q

When must you call the NRC after a reportable event?

A

Within 24 hours

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87
Q

When must you send a written letter to the NRC after a reportable event?

A

Within 15 days

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88
Q

When must you notify the referring physician after a reportable event?

A

Within 24 hours

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89
Q

Who should notify the pt after a reportable event?

A

Nuclear medicine radiologist or referring physician

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90
Q

What mistakes may qualify as reportable events (if the dose is high enough)?

A
  • Wrong dose (at least 20% more than it should have been)
  • Wrong drug
  • Wrong route
  • Wrong pt
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91
Q

How soon after receipt of a radioactive package must the initial survey be done?

A

Within 3 working hours

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92
Q

When is a radioactive package considered beyond allowable limits?

A

> 6600 dpm/300 cm^2 (need to contact the shipper and the NRC)

Note: This is during the initial survey (using a Geiger-Muller counter at the package surface and 1 meter away as well as a wipe test of all surfaces).

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93
Q

What radioactive package label indicates that no special handling is required?

A

White 1 label

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94
Q

What is the dose limit for a white 1 label package?

A

Must be < 0.5 mrem/hour at surface (and 0 mrem/hour at 1 meter)

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95
Q

What is the dose limit for a yellow 1 label package?

A

Must be < 50 mrem/hour at surface (and < 1 mrem/hour at 1 meter)

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96
Q

What is the dose limit for a yellow 2 label package?

A

Must be < 200 mrem/hour at surface (and < 10 mrem/hour at 1 meter)

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97
Q

What is the transportation index for a white 1 label package?

A

no transportation index (rate at 1 meter is so low)

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98
Q

What is the transportation index for a yellow 1 label package?

A

TI < 1.0 mrem per hour

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99
Q

What is the transportation index for a yellow 2 label package?

A

TI > 1.0 mrem per hour

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100
Q

What is a common carrier

A

A truck that carries regular packages and radioactive material

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101
Q

Transportation index should not exceed ______ for common carriers

A

10 mrem/hour

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102
Q

Surface rate should not exceed ______ for common carriers

A

200 mrem

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103
Q

The sum of multiple radioactive packages traveling together should not exceed _____

A

50 mrem

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104
Q

What is the allowable limit of Tc-99m radionuclide purity?

A

0.15 microcuries of Mo per 1 millicurie of Tc

Note: This is tested in a dose calibrator with lead shields.

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105
Q

What energy photons are you looking for when testing for Tc-99m radionuclide purity?

A

700 keV (photons from Molybdenum breakthrough)

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106
Q

What is the allowable limit for Tc-99m chemical purity?

A

< 10 micrograms Al per 1 mL Tc-99m

Note: This is tested with pH paper.

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107
Q

What are the types of Tc-99m purity?

A
  • Radionuclide purity (molybdenum breakthrough, tested with dose callibrator)
  • Chemical purity (aluminum breakthrough, tested with pH paper)
  • Radiochemical purity (free Tc contamination, tested with thin layer chromatography)
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108
Q

What is the allowable limit for radiochemical purity of Tc-99m?

A
  • 91% (for most)
  • 92% (for Tc-99m sulfur colloid)
  • 95% (for Tc-99m TcO4)
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109
Q

If a Tc-99m dose containing free Tc is given, what will show up on scans?

A
  • Gastric uptake
  • Salivary gland uptake
  • Thyroid uptake
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110
Q

When is transient equilibrium obtained for a Tc-Mo generator?

A

4 daughter half lives (24 hours)

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111
Q

What appears hotter on non-attenuation corrected images?

A
  • Skin
  • Lungs
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112
Q

Does PET imaging use a collimator

A

2D PET uses septa collimator (to reject scatter photons)

3D PET does not use a collimator (fast coincidence detector)

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113
Q

Which is more sensitive: 2D or 3D PET?

A

3D PET is more sensitive

Note: Lack of septa collimator results in more true, scattered, and random coincidences.

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114
Q

Which has a larger field of view for true coincidences: 2D or 3D PET?

A

3D PET has a larger field of view

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115
Q

Which requires more radiotracer: 2D or 3D PET?

A

2D PET requires more radiotracer

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116
Q

In obese pts, SUVs are ______

A

Overestimated

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117
Q

If scan time is delayed, SUVs will be ______

A

Overestimated (higher FDG values)

118
Q

High blood glucose results in _______ SUVs

A

Lower SUVs (underestimated)

119
Q

IV dose extravasation will result in ________ SUVs

A

Lower SUVs (underestimated)

120
Q

More iterations during iterative reconstruction results in _____ SUVs

A

Higher SUVs (overestimated)

121
Q

Dose units for exposure

A

C/Kg (Charge created in the air/mass of that air)

122
Q

Dose units for absorbed dose

A

J/Kg (energy deposited per unit kg of material)

Note: Commonly used units are Gray and Rads.

123
Q

1 Gy = ? rads

A

1 Gy = 100 rads

124
Q

What is equivalent dose?

A

The absorbed dose adjusted for the type of radiation (alpha particles do more damage than electrons)

125
Q

What is the weight factor for alpha particles used to calculate equivalent doses?

A

20

Note: For xrays and gamma rays its 1 (absorbed dose = equivalent dose).

126
Q

What are the units for effective dose?

A

Sv

127
Q

What is effecive dose?

A

The equivalent dose adjusted for how radiosensitive the tissues are that absorbed the dose (best measure of cancer risk)

128
Q

What is the threshold for stochastic effects of radioation?

A

There is no threshold for stochastic effects

129
Q

Is severity of stochastic effects dose related?

A

No (but probability of stochastic effects increases with increasing dose)

130
Q

What are the stochastic effects of radiation?

A
  • Cancer risk
  • Heritable effects
131
Q

What is the air kerma?

A

A measure of the absorbed dose in air during fluoroscopy (Gy/min)

Note: This only accounts for the primary interaction of photons on tissue atoms (not the secondary production of scatter electrons, which also contribute to overall dose).

132
Q

If distance doubles, the air kerma…

A

Decreases by a factor of 4 (inverse square law)

133
Q

The air kerma tells you…

A

Deterministic effect risk

134
Q

What is the kerma area product?

A

The kerma area times the cross sectional area exposed

135
Q

The kerma area product tells you…

A

Stochastic effect risk

136
Q

If distance doubles, kerma air product…

A

Stays the same (kerma air product is independent of distance)

137
Q

How does collimation affect kerma air product?

A

Collimation decreases KAP (decreased cross sectional area exposed)

138
Q

What is the cumulative air kerma?

A

A total of all the air kerma values for individual exposures

Note: This is described at a specific interventional reference point (15 cm towards the xray tube).

139
Q

What is the CT dose index?

A

The radiation dose of a CT exam, normalized to beam width (based on dose absorbed by a CT phantom)

140
Q

How big is the CT phantom for CTDI measurement?

A

32 cm in diameter

141
Q

If the pt is more obese than the CT phantom, CTDI will be _______

A

Overestimated (obese pts receive less radiation per Kg)

142
Q

The CTDI for a pediatric pt will be ______ if the standard CT phantom is used

A

Underestimated (pediatric pts would receive more radiation per Kg than the phantom)

143
Q

How do you calculate a weighted CTDI?

A

(1/3 central CTDI) + (2/3 peripheral CTDI)

Note: The CT phantom has 4 peripheral ionization chambers and 1 central chamber.

144
Q

How do you calculate the volume CTDI?

A

Weighted CTDI divided by CT pitch

145
Q

What is the ACR reference dose for a head CT?

A

Volume CTDI of 75 mGy

146
Q

What is the ACR reference dose for an adult abdominal CT?

A

Volume CTDI of 25 mGy

147
Q

The ACR sets the reference dose for CT scans at…

A

The 75th percentile

148
Q

What is the ACR reference dose for a pediatric abdominal CT?

A

Volume CTDI of 20 mGy (5 year old)

149
Q

How do you calculate the dose product length for CT?

A

Volume CTDI times the length of the scan (in cm)

150
Q

How do you calculate the effective dose for CT?

A

dose length product x k (a body part constant)

151
Q

Direct vs indirect radiation

A

Direct radiation acts on DNA (uncommon in xray imaging)

Indirect radiation acts on water in the cytoplasm, creating free radicals that damage DNA (more common in xray imaging)

152
Q

Radiation dose needed to induce acute radiation syndrome in bone marrow

A

> 2 Gy (latent period of 1-6 weeks)

Note: It is possible to survive.

153
Q

Radiation dose needed to induce acute radiation syndrome in the GI tract

A

> 8 Gy (latent period of 5-7 days)

Note: Death occurs within 2 weeks.

154
Q

Radiation dose needed to induce acute radiation syndrome in the CNS

A

> 20-50 Gy (latent period of 4-6 hours)

Note: Death occurs within 3 days.

155
Q

Next step: possible acute radiation syndrome with no vomiting or skin redness (whole body dose < 1 Gy)

A

Surveillance for 5 weeks

156
Q

Next step: possible acute radiation syndrome with vomiting 2-3 hours after exposure or skin redness 12-24 hours after exposure (whole body dose 1-2 Gy)

A

Consider general hospital (at mimimum surveillance for 3 weeks)

157
Q

Next step: possible acute radiation syndrome with vomiting 1-2 hours after exposure or skin redness 8-15 hours after exposure (whole body dose 2-4 Gy)

A

Hospitalize in a burn center

158
Q

Next step: possible acute radiation syndrome with vomiting within 1 hour after exposure or skin redness 1-6 hours after exposure (whole body dose > 4 Gy)

A

Hospitalize in a specialized radiation center

159
Q

What is the radiation dose and onset for early transient erythema?

A

2 Gy skin dose (onset in hours)

160
Q

What is the radiation dose and onset for severe “robust” erythema?

A

6 Gy skin dose (onset in 1 week)

161
Q

What is the radiation dose and onset for telangiectasia?

A

10 Gy skin dose (onset in 52 weeks)

162
Q

What is the radiation dose and onset for dry desquamation?

A

13 Gy skin dose (onset in 4 weeks)

163
Q

What is the radiation dose and onset for moist desquamation/ulceration?

A

18 Gy skin dose (onset in 4 weeks)

164
Q

What is the radiation dose and onset for secondary ulceration?

A

24 Gy skin dose (onset in > 6 weeks)

165
Q

What is the radiation dose and onset for temporary epilation?

A

3 Gy (onset in 21 days)

166
Q

What is the radiation dose and onset for permanent epilation?

A

7 Gy (onset in 21 days)

167
Q

What is the cell cycle stage most sensitive to radiation?

A

M phase

Note: M > G2 > G1 > S (S phase is the least).

168
Q

What is the most radiosensitive part of the GI tract?

A

Small bowel

169
Q

What is the most radiosensitive blood cell type?

A

Lymphocytes

Note: A dose of 0.25 Gy is enough to depress the amount of lymphocytes circulating in blood.

170
Q

What is the effect of a radiation dose < 50 mGy to a 0-2 week old embryo?

A

Probably nothing (small chance of spontaneous abortion)

171
Q

What is the effect of a radiation dose < 50 mGy to a > 2 week old embryo/fetus?

A

Probably nothing (dose is small)

172
Q

What is the effect of a radiation dose 50-100 mGy to a 0-2 week old embryo?

A

Nothin or spontaneous abortion (“all or nothing”)

173
Q

What is the effect of a radiation dose 50-100 mGy to a > 25 week old embryo/fetus?

A

Probably no teratogenic effects

174
Q

What is the gestational age at highest risk of teratogenic effects of radiation?

A

8-15 weeks (this is when neuronal development occurs)

175
Q

Elective abortion should be considered after the embryo/fetus has been exposed to how much radiation?

A

> 100 mGy

176
Q

Which MRI signal relies on free induction decay (rather than creating an echo)?

A

T2*

177
Q

How can you identify a spin echo sequence by the pulse sequence diagram?

A

There will be a 180 degree RF pulse at time = 1/2 TE

178
Q

How can you recognize a gradient echo sequence by the pulse sequence diagram?

A

There will be no 180 degree RF pulse

179
Q

How can you recognize a fast spin echo sequence by the pulse sequence diagram?

A

There will be multiple back to back 180 degree RF pulses (after the initial 90 degree RF pulse)

180
Q

How can you recognize an inversion recovery sequence by the pulse sequence diagram?

A

There will be a 180 degree RF pulse before the initial 90 degree RF pulse

181
Q

What type of sequence is this?

A

Spin echo

Note: 90 degree RF followed by 180 degree RF.

182
Q

What type of sequence is this?

A

Fast spin echo

Note: Multiple 180 degree RFs after initial 90 degree RF.

183
Q

What type of sequence is this?

A

Inversion recovery

Note: 180 degree RF before initial 90 degree RF.

184
Q

What type of sequence is this?

A

Gradient echo (GRE)

Note: No 180 degree RF pulse.

185
Q

T1 is determined by…

A

Spin-lattice interactions (and is equal to the time to reach 63% recovery of longitudinal magnetization)

186
Q

T2 is determined by…

A

Spin-spin interactions (and is equal to the time to reach 37% decay of in phase)

187
Q

T2* is determined by…

A

Spin-spin interactions PLUS the non-uniformity of the magnetic field

188
Q

T1 shortening appears _______ on the image

A

Bright

189
Q

T2 shortening appears ______ on the image

A

Dark

190
Q

What should TR/TE be for T1 weighting?

A

Short TR
Short TE

191
Q

What should TR/TE be for T2 weighting?

A

Long TR
Long TE

192
Q

What should TR/TE be for PD weighting?

A

Long TR
Short TE

Note: Long TR minimizes T1 weighting and short TE minimizes T2 weighting.

193
Q

What is considered a short TR for spin echo?

A

250-700 ms

194
Q

What is considered a long TR for spin echo?

A

> 2000 ms

195
Q

What is considered a short TE for spin echo?

A

10-25 ms

196
Q

What is considered a long TE for spin echo?

A

> 60 ms

197
Q

What is considered a short TR for gradient echo?

A

< 50 ms

198
Q

What is considered a long TR for gradient echo?

A

> 100 ms

199
Q

What is considered a short TE for gradient echo?

A

1-5 ms

200
Q

What is considered a long TE for gradient echo?

A

> 10 ms

201
Q

How do you calculate the table time for a standard sequence?

A

TR x phase matrix x NEX

NEX: # of excitations (per TR)

202
Q

How do you calculate the table time for a 3D sequence?

A

TR x phase matrix x NEX x # of slices

NEX: # of excitations (per TR)

203
Q

How can you estimate the table time for a fast spin echo sequence?

A

1/echotrain length

204
Q

How can you make MRI slices thinner?

A
  • Increase the slice selection gradient (make it steeper)
  • Decrease the transmit bandwidth
205
Q

How will decreasing the slice slection gradient affect slice thickness?

A

Thicker slices

206
Q

How is MRI signal to noise ratio affected by making the slices thicker?

A

Increased signal to noise ratio

207
Q

How is MRI signal to noise ratio affected by a larger field of view?

A

Increased signal to noise ratio

208
Q

How is MRI signal to noise ratio affected by a larger matrix?

A

Decreased signal to noise ratio

209
Q

How is MRI signal to noise ratio affected by a greater magnetic field strength?

A

Increased signal to noise ratio

210
Q

How is MRI signal to noise ratio affected by a greater receiver bandwidth?

A

Decreased signal to noise ratio

211
Q

How is MRI signal to noise ratio affected by a greater transmit bandwidth?

A

Increased signal to noise ratio

212
Q

How is MRI signal to noise ratio affected by more excitations per slice?

A

Increased signal to noise ratio

213
Q

How is MRI signal to noise ratio affected by utilizing partial K space sampling?

A

Decreased signal to noise ratio

214
Q

How is MRI spatial resolution affected by thicker slices?

A

Decreased spatial resolution

215
Q

How is MRI spatial resolution affected by a larger field of view?

A

Decreased spatial resolution

216
Q

How is MRI spatial resolution affected by a larger matrix?

A

Increased spatial resolution

217
Q

How is MRI spatial resolution affected by a greater magnetic field strength?

A

No effect on spatial resolution

218
Q

How is MRI spatial resolution affected by a greater receiver bandwidth?

A

No effect on spatial resolution

219
Q

How is MRI spatial resolution affected by a greater transmit bandwidth?

A

Decreased spatial resolution

220
Q

How is MRI spatial resolution affected by more excitations per slice?

A

No effect on spatial resolution

221
Q

How is MRI spatial resolution affected by utlizing partial K space sampling?

A

No effect on spatial resolution

222
Q

How is the duration of an MRI exam affected by thicker slices?

A

No effect on table time

223
Q

How is the duration of an MRI exam affected by a larger field of view?

A

No effect on table time

224
Q

How is the duration of an MRI exam affected by a larger matrix?

A

Increased table time

225
Q

How is the duration of an MRI exam affected by a greater magnetic field strength?

A

No effect on table time

226
Q

How is the duration of an MRI exam affected by a greater receiver bandwidth?

A

Decreased table time

227
Q

How is the duration of an MRI exam affected by a greater transmit bandwidth?

A

No effect on table time

228
Q

How is the duration of an MRI exam affected by more excitations per slice?

A

Increased table time

229
Q

How is the duration of an MRI exam affected by utilizing partial k space sampling?

A

Decreased table time

230
Q

What does a smaller receiver bandwidth do?

A

Increases signal to noise ratio

231
Q

What does a smaller transmit bandwidth do?

A
  • Decreases signal to noise ratio
  • Makes slices thinner
232
Q

How are thinner MRI slices a tradeoff?

A

Improved spatial resolution, but more noise (lower SNR)

233
Q

What artifacts are made worse by higher magnetic fields?

A
  • Type 1 chemical shift artifact
  • Susceptibility artifacts (e.g. metal)
234
Q

What artifacts are minimized by using a thicker receiver bandwidth?

A
  • Type 1 chemical shift artifact
  • Susceptibility artifacts (e.g. metal)
235
Q

Why is increasing the number of excitations per TR a tradeoff?

A

Improved SNR, but increased table time

236
Q

What is the best sequence for signal to noise ratio?

A

PD

237
Q

What are the out of phase and in phase times for a 1.5 T MRI?

A

OOP: 2.2 ms
IP: 4.4 ms

OR

OOP: 6.6 ms
IP: 8.8 ms

238
Q

What are the out of phase and in phase times for a 3.0 T MRI?

A

OOP: 1.1 ms
IP: 2.2 ms

OR

OOP: 3.3 ms
IP: 4.4 ms

239
Q

fMRI depends on…

A

T2* effects (uses blood oxygen level dependent imaging)

240
Q

What MRI sequence is used for cardiac “bright blood”?

A

Gradient echo

241
Q

What MRI sequence is used for cardiac “black blood”?

A

Double inversion spin echo

242
Q

What MRI sequence is used to null myocardium for cardiac MRIs?

A

Inversion recovery

Note: The inversion time is chosen to match the patients myocardium.

243
Q

What is the only macrolytic, non-ionic commonly used MRI contrast agent?

A

Gadobutrol (AKA Gadavist)

Note: All the other main MRI contrast agents are linear, ionic.

244
Q

Which major MRI contrast agent has the highest risk of nephrogenic systemic fibrosis?

A

Gadopentetate (AKA Magnevist)

245
Q

Which MRI contrast agent has a 50% hepatocyte uptake?

A

Gadoxetate (AKA Eovist)

Note: Gadobenate (AKA Multihance) has 5% hepatocyte uptake.

246
Q

How should you minimize fat signal on post gadolinium MRI sequences?

A

Fat saturation

Note: Do NOT use STIR (the fat inversion time is too similar to gad and you will null contrast signal).

247
Q

How does gadolinium work as an MRI contrast agent?

A

Increasing spin-lattice interactions (shortens T1)

248
Q

When should you be worried about nephrogenic systemic fibrosis due to gadolinium?

A
  • Renal failure (GFR < 30)
  • Pro-inflammatory states (acute illness)
  • Using an older contrast agent like Gadodiamide (AKA Omniscan)
249
Q

What are the high energy radionuclides?

A
  • I-131
  • F-18 (511 keV)
  • Germanium-68/Gallium-68 (511 keV, used for QA)
250
Q

Which MRI artifacts mostly occur in the phase encoding direction?

A
  • Aliasing
  • Gibbs/truncation artifact
  • Motion artifact
  • Zipper artifact
251
Q

Which MRI artifacts mostly occur in the frequency encoding direction?

A

Type 1 chemical shift artifact

252
Q

Which MRI artifacts occur in the phase encoding AND frequency encoding directions?

A
  • Type 2 chemical shift (AKA india ink)
  • Gibbs artifact (AKA truncation), though this is mostly in the phase encoding direction
253
Q

In what direction does this artifact occur?

A

Phase encoding direction

Note: This is aliasing.

254
Q

How can you fix this artifact?

A
  • Increase the field of view
  • Change the phase encoding direction

Note: This is aliasing (due to a small field of view in the phase encoding direction).

255
Q

In what direction does this artifact occur?

A

Frequency encoding direction only

Note: This is type 1 chemical shift artifact.

256
Q

How can you minimize this artifact?

A
  • Bigger pixels
  • Fat suppression
  • Increase receiver bandwidth
  • Use a weaker magnet

Note: This is type 1 chemical shift artifact (due to differences in resonant frequencies at the interface between fat-water).

257
Q

In what direction does this artifact occur?

A

Both the phase and frequency encoding direction

Note: This is the type 2 chemical shift (India ink) artifact.

258
Q

How can you minimize this artifact?

A
  • Adjust the TE
  • Perform spin echo sequence instead

Note: This is the type 2 chemical shift/India ink artifact (due to differences in resonant requencies that oppose each other at specific TE intervals).

259
Q

This artifact only occurs on what type of sequences?

A

Gradient echo sequences

Note: This is the type 2 chemical shift (India ink) artifact.

260
Q

What type of artifact is this?

A

Gibbs (AKA truncation) artifact

Note: This is due to a limited field of view.

261
Q

In what direction does this artifact occur?

A

Most often the phase encoding direction (but can also occur in the frequency encoding direction)

Note: This is the Gibbs/truncation artifact (due to limited sampling of free induction decay).

262
Q

How can you minimize this artifact?

A
  • Use a bigger matrix
  • Decrease bandwidth
  • Decrease pixel size

Note: This is the Gibbs/truncation artifact (due to a limited sampling of free induction decay).

263
Q

How can you minimize this artifact?

A

Decrease pixel size (increase phase encoding steps or decrease field of view)

264
Q

The center of K space contains…

A

Information about gross form and contrast

Note: The periphery of k space contains information about spatial resolution.

265
Q

In which direction does this artifact occur?

A

Phase encoding direction

Note: This is motion artifact.

266
Q

How can you minimize this artfact?

A
  • Use saturation pulses
  • Respiratory gating
  • Faster sequences (e.g. BLADE, PROPELLER)

Note: This is the motion artifact.

267
Q

What type of artifact is this?

A

Cross talk artifact (due to overlapping slices)

268
Q

How can you minimize this artifact?

A
  • Increase slice gap
  • Interleave slices (do all odd slices, then all even slices)
269
Q

What are two common types of motion artifact on MRI?

A
  • Breathing artifact (due to diaphragm motion)
  • Pulsation artifact (due to blood vessel motion)
270
Q

At what angle does magic angle artifact occur?

A

55 degrees (between tendon and main magnetic field)

Note: You see this more with short TE sequences (not seen on T2 sequences).

271
Q

What artifact is this?

A

Zipper artifact (caused by poor shielding letting RF interference through)

Note: Did you leave the MRI room door open?

272
Q

How can you minimize this artfact?

A
  • Close the MRI room door (if open)
  • Remove all electronic devices from MRI room (e.g. pulse ox)
  • Call the MRI tech to repair RF shielding

Note: This is zipper artifact (due to poor shielding from RF interference).

273
Q

This artifact is worse on what type of sequences?

A

GRE sequences

Note: This is magnetic field inhomogeneity artifact (causing geometric distortion).

274
Q

What would make this artifact worse?

A
  • Using GRE sequences
  • Using a bigger magnetic field strength

Note: This is susceptability artifact caused by metal augmenting the local magnetic field.

275
Q

How can you minimize this artifact?

A
  • Use spin echo sequences (not GRE)
  • Use lower magnetic field strength
  • Use higher receiver bandwidth
  • Use short echo train spacing
  • Use thinner slices

Note: This is susceptability artifact caused by metal augmenting the local magnetic field.

276
Q

What is the cause of this artifact?

A

Large gradient changes causing geometric distortion and non-uniformity (most noticible on diffusion images)

Note: This is Eddy current artifact.

277
Q

How can you minimize this artifact?

A

Shimming (passive and active) to reduce magnetic field inhomogeneity

Note: This is magnetic field inhomogeneity artifact (which can cause poor fat saturation).

278
Q

How can you minimize this artifact?

A

Optimize the sequence of gradient pulses

Note: This is caused by eddie currents (due to large gradient changes, especially on diffusion imaging).

279
Q

What is the cause of this artifact?

A

Radiowaves are shortened enough by dielectric effects to match the length of a body part (creating a standing wave)

Note: This is a dielectric effect artifact.

280
Q

How can you minimize this artifact?

A
  • Use parallel RF transmision (to create longer FR waves)
  • Use dielectric pads
  • Use weaker magnet (1.5 T)

Note: This is dielectric effect artifact.

281
Q

How can you fix this artifact?

A

Reconstruct the image again (from the dame data)

Note: This is herringbone or crisscross artifact (due to a data processing/reconstruction error).

282
Q

What are the MRI zones?

A
  • Zone I (far from the magnet)
  • Zone II (MRI screening room)
  • Zone III (locked control room)
  • Zone IV (MRI room)
283
Q

Which MRI zones are restricted?

A

Zones III and IV (screened people only)

Note: Zones I and II are unrestricted (prescreen)

284
Q

In what scenarios should you quench the MRI magnet?

A
  • Life threatening fire in the MRI room
  • Someone is pinned by a metal object

Note: A pt coding is not a reason to quench (unless they’re coding because they are pinned by an oxygen tank).

285
Q

What is the 5G line?

A

A circle drawn around the MRI machine that indicates risk to implantable devices (e.g. pacemaker, neurostimulation, insulin pump)

Note: Inside this line magnetic forces are above 5 gauss.

286
Q

Which sequences have the highest risk of causing hearing damage?

A

Echo planar sequences (loud noises are due to gradient switching)

287
Q

What sequences are most likely to cause neurostimulation?

A

Echo planar (due to rapid gradient switching and high-bandwidth readouts)

288
Q

What is the specific absorption rate for MRI?

A

(B^2) x (Alpha^2) x (duty cycle)

B: Magnetic field strength
Alpha: Flip angle
Duty cycle: How short your TR is

289
Q

What is the limit for specific absorption rate?

A

4 W/Kg

290
Q

How will doubling the TR affect the duty cycle?

A

Half the duty cycle

291
Q

Can you continue breastfeeding after getting IV contrast?

A

No, it is recommended to stop breastfeeding (for both iodinated and gadolinium contrast)

292
Q

What radionuclides are not safe when breastfeeding?

A
  • Tc-99m (can resume in 12-24 hours)
  • I-123 (can resume in 2-3 days)
  • Gallium-67 (don’t resume)
  • I-131 (don’t resume)

Core (98 decks)

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