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Physics review Flashcards

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1
Q

TRUE or FALSE: Gadolinium crosses the placenta, enters the amniotic fluid and is ingested by the fetus. The text suggest avoiding gadolinium in pregnant patients.

A

True

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2
Q

TRUE or FALSE: There have been no known long-term adverse biological effects associated with extended exposure to the magnetic fields in MR imaging. However, several reversible effects can be observed.

A

True

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3
Q

What is the rotational force in the MRI environment?

A

moving or twisting

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4
Q

What is the translational force in the MRI environment?

A

violent attraction

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5
Q

What is the missile force in the MRI environment?

A

metal object becomes airborn

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6
Q

In the MRI environment, the translational force increases how?

A

close to isocenter

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7
Q

In the MRI environment, the translational force decreases how?

A

away from isocenter

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8
Q

What is the direction of the static fields of closed bore superconducting magnet?

A

Bo is horizontal

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9
Q

What is the direction of the static fields of vertical magnets for open permanent magnet:

A

Bo is vertical

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10
Q

Where can/do MRI technologists reference the safety of an implanted device?

A
  • Dr. Frank Shellock’s reference manual
  • Institute for Magnetic Resonance, Safety and Education and Research
  • the manufacturer of the device
  • www.mrisafety.com
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11
Q

Concerning foreign bodies in the eyes … what is more accurate?

A

computed tomography

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12
Q

Concerning foreign bodies in the eyes … what is adequate for screening?

A

radiography

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13
Q

The FDA limits of Bo for babies is what?

A

4T

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14
Q

The FDA limits of Bo for patients 1 month+ is what?

A

8T

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15
Q

Concerning SAR, what is the FDA limit for heating?

A

1-degree Celcius in the core

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16
Q

What are the units of SAR?

A

watts per kilogram (W/kg)

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17
Q

What is important when monitoring SAR?

A

the patient’s weight

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18
Q

What does SAR stand for?

A

specific absorption rate

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19
Q

What concerns for MRI patients apply to pregnant patients?

A

No known biological effects to fetus but prefer to delay until after 1st trimester

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20
Q

What concerns for MRI patients apply to pregnant employees?

A

Can enter the scan room but should leave before RF and gradient fields are employed. Make informed decisions.

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21
Q

What concerns for MRI patients apply to patients in medical emergency?

A

remove from Zone 4 before start CPR

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22
Q

What is the FDA limit of magnetic field strengths for babies up to 1 month old?

A

4T

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23
Q

What is the FDA limit of magnetic field strengths for those older than 1 month?

A

8T

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24
Q

Which of the following does the text state as reported accidents and near misses in MRI? Choose all that apply …

A
  • burns
  • device failures
  • contrast reactions
  • death
  • ferromagnetic metal objects flying
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25
Q

How should unconscious, comatose, sedated or hearing-impaired patients be monitored while in MRI? Choose all that apply …

A
  • verbally
  • visually
  • with pulse oximetry
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26
Q

What does nagnetophosphenes mean?

A

Patient may report seeing flashes of light or “seeing stars”

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27
Q

What does Bo mean?

A

main/static magnetic field

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28
Q

What does hemodynamic effect mean?

A

reversible amplitude of the T-wave

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29
Q

What does quench mean?

A

helium escapes

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30
Q

What does cryogens mean?

A

cools superconducting

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31
Q

What does fringe field mean?

A

Magnetic field outside the bore. Not confined to ceilings, floors, or walls. Shielded to 5G.

32
Q

What is MRI Facility Zone 1?

A

free to general public

33
Q

What is MRI Facility Zone 2?

A

waiting or dressing room

34
Q

What is MRI Facility Zone 3?

A

b/t Zone 2 and the scanner

35
Q

What is MRI Facility Zone 4?

A

scan room

36
Q

Which magnetic field spatially encode data, altering the MF in a linear fashion?

A

gradients

37
Q

Who should be screened for MRI safety?

A

Screen every patient every time and verify with metal detector

38
Q

In 2001, a 6-year old patient was killed in a MRI scanner.

Which of the following are correct concerning this tragedy? Choose all correct.

A
  • caused by a ferromagnetic oxygen tank
  • lead to the publication of a White Paper called “ACR Guidance Document for Safe MR Practices”
  • published in 2002
  • intended to provide guidelines for the development and implementation of safety policies and procedures
  • has been reviewed and updated periodically since publication
39
Q

What was the text’s example of a missile effect?

A

terminal velocity of a paperclip can reach 40mph

40
Q

The green box with MR inside safety label means what?

A

Item poses no known hazards in all MRI environments

41
Q

The yellow triangle with MR inside safety label means what?

A

Item poses no known hazards in a specified MRI environment with specified conditions of use

42
Q

The red circle with a line thru MR safety label means what?

A

Item is known to pose hazards in all MRI environments

43
Q

TRUE or FALSE: An implant that is safe for 3 T is automatically deemed safe at 1.5 T.

A

False

44
Q

What is the most likely side effect of RF fields?

A

heating of tissue, antennae effects, thermal injuries

45
Q

What is the most likely side effect of gradients?

A

peripheral nerve stimulation, magnetophosphenes, noise

46
Q

What is the most likely side effect of static field?

A

associated with devices, implants, and projectiles

47
Q

What is the best device to use when monitoring a patient’s status in MRI?

A

Pulse ox

48
Q

Which of the following describe T1 Recovery? Choose all correct …

A
  • spin lattice relaxation

* caused by the nuclei giving up their energy to the surrounding environment or lattice

49
Q

Which of the following describe the purpose of gradients in MRI? Choose all correct …

A
  • After the main magnetic field in a linear fashion

* Spatially encode data

50
Q

Which way does the main magnetic field run in superconducting magnets?

A

Along the bore of the magnet (horizontal)

51
Q

Identify the two factors that determine which hydrogen nuclei align parallel and which align anti-parallel with the main magnetic field.

A
  • The strength of the external magnetic field

* The thermal energy level of the nuclei

52
Q

What are the guidelines for pregnant employees?

A

Pregnant employees may enter the scan room, but should leave before scanning begins.

53
Q

What would you do in the event of a CODE BLUE in MRI? (Select all that apply)

A
  • Begin CPR
  • Activate the Code Blue response process (push the Code Blue button)
  • Get the patient out of the scanner and into Zone III; locking the scan room door and monitoring it when other Code Team members arrive
54
Q

What are the two results of resonance? Choose all correct …

A
  • The NMV moves out of alignment and away from BO

* The magnetic moments of hydrogen nuclei move into phase with each other

55
Q

What must be done prior to anyone entering the scan room? Select the best answer …

A

The completed screening sheet must be signed by a level II staff member and the patient must be scanned with the metal detector

56
Q

What is another term for T2 Decay?

A

Spin-spin relaxation

57
Q

What does SAR stand for?

A

Specific Absorption Rate

58
Q

Which of the following best describe spin-lattice relaxation? Choose all correct …

A
  • T1 Recovery

* Nuclei give up energy to the surrounding environment, resulting in longitudinal recovery.

59
Q

What makes a nucleus an MR active nucleus? Choose all correct …

A
  • Odd mass numbers

* Nuclei with a net spin or angular momentum

60
Q

We always scan pregnant patients with contrast.

A

False

We ONLY scan pregnant patients after discussing it with a radiologist (who will determine risk vs. benefit) and having the patient sign a release form. It is recommended to avoidgiving contrast to pregnant women.

61
Q

What effect does the magneto-hemodynamic effect have? Is this a permanent effect? Choose all correct …

A
  • Increase in the amplitude of the “T” wave on EKG gating.

* Reversible effect– EKG tracing returns to normal when the patient is removed from the static magnetic field.

62
Q

What is the T2 relaxation time of tissue?

Hint: Think about which axis T2 relaxation is occurring in (longitudinal vs. transverse) and whether T2 relaxation indicates recovery vs. decay.

A

The time it takes 63% of the transverse magnetization to decay in the tissue.

<strong>T2 relaxation</strong> results in <strong>decay</strong> or loss of coherent <strong>transverse</strong> magnetization. It is an exponential process and the T2 relaxation time of a tissue is its time constant of decay, or the time it takes 63% of the transverse magnetization to be lost. See pages 16-17 in the text.

63
Q

What does the Larmor Equation calculate?

A

The precessional frequency

64
Q

Where do we look up the safety of an implanted device? Check all that apply …

A
  • www.MRISafety.comLinks to an external site.
  • Shellock’s reference manual
  • The manufacturer’s website
65
Q

What is the terminal velocity of a paperclip at 1.5T?

A

40 mph

66
Q

The gyromagnetic ratio expresses the relationship between the angular momentum and the magnetic moment of each MR active nucleus.

A

True

67
Q

The “warm zone” in MRI is the scan room itself.

A

False

The “warm zone” in MRI is Zone III, or the controlled area just outside of the scan room, which usually includes the patient holding and control room area.

68
Q

Identify which of the following describe a “fringe field.” Choose all correct …

A
  • The stray magnetic field outside the bore of the magnet.
  • Active or passive shielding is used to reduce the size of the fringe field.
  • The fringe field is not confined by walls, floors, or ceilings.
69
Q

What does the net magnetization vector (NMV) represent?

A

The relative balance of spin-up to spin-down nuclei

70
Q

What are the three types of motion present in an atom? Choose all correct …

A
  • Electrons spinning on their own axis.
  • Electrons orbiting the nucleus.
  • The nucleus itself spinning about its own axis.
71
Q

Which way does the main magnetic field run in permanent magnets?

A

Vertically

72
Q

For resonance of hydrogen to occur, RF at exactly the Larmor frequency of hydrogen must be applied.

A

True

73
Q

What is the gyromagnetic ratio of hydrogen?

A

42.57 MHz/T

74
Q

Select the three components of the magnetic field from those listed below.

A
  • Static Magnetic Field
  • Radiofrequency Fields
  • Time Varying Magnetic Fields
75
Q

What happens to the alignment of hydrogen protons when placed in an external magnetic field? Check all that apply …

A
  • The magnetic moments of the nuclei align with or against the main magnetic field.
  • Slightly more nuclei line up with the main magnetic field than against it.

Physics (15 decks)

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