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Static Magnetic Fields Flashcards

1
Q

If an object is magnetically saturated, it means that:

The object is wet and should not be used in the magnetic field

An increase in the applied external magnetic field cannot increase the magnetization of the object further

The object is no longer considered magnetic

Condensation has formed on the object while it was in the static magnetic field

A

An increase in the applied external magnetic field cannot increase the magnetization of the object further

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2
Q

Within the static magnetic field, where is the rotational force/torque exerted on a metallic object the greatest?

Mouth of the bore

Wall of the bore

Entrance to Zone 4

Isocenter

A

Isocenter

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3
Q

An object deflects 45 degrees during deflection testing. What force(s) has the most effect on the device?

The external magnetic field

Gravity

Scarring within the patient due to healing

Gravity and the external magnetic field are exerting equal force on the device

A

Gravity and the external magnetic field are exerting equal force on the device

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4
Q

The twisting force on a ferromagnetic object as it attempts to align parallel to the external magnetic field is called _____.

Missile effect

Translation

Torque

Magnitude

A

Torque

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5
Q

Mechanical forces related to the static magnetic field include translational (missle), rotational (torque), and Lenz effects. True or False?

True

False

A

True

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6
Q

1T converted to Gauss would be:

10 Gauss

100 Gauss

1,000 Gauss

10,000 Gauss

A

10,000 Gauss

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7
Q

rimary concerns with static magnetic fields are __________ .

Translation and rotation (torque) forces

Focal heating

Induced voltages

Retention

A

Translation and rotation (torque) forces

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8
Q

If there is an area that reads 16T/m on a spatial gradient map, that means:

The strength of the magnetic field would change by 16 Tesla if that same localized rate of change in that small area were to occur over 1 meter of distance.

The strength of the magnetic field would change by 16 Tesla if an implant were to be spread out over 1 foot of distance.

The maximum field strength of that area within the magnet is 16T

The magnet will change from 1T to 16T across the length of the bore.

A

The strength of the magnetic field would change by 16 Tesla if that same localized rate of change in that small area were to occur over 1 meter of distance.

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9
Q

Within the magnetic field, torque/rotational force will be the greatest at __________.

mouth of the bore

edge of gradient coil

isocenter

within transmit coil

A

isocenter

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10
Q

What type of map is this?

Spatial Gradient Map

Gradient Map

RF Deposition Map

B0 map

A

B0 map

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11
Q

Shielding of the magnet has what effect on the magnetic field?

Increases the size of the fringe field and decreases the MSG

Increases both the size of the fringe field and the MSG

Decreases both the size of the fringe field and the MSG

Decreases the size of the fringe field and increases the MSG

A

Decreases the size of the fringe field and increases the MSG

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12
Q

The concentration of the orbiting magnetic particles in space within the magnetic field is termed:

Proton Density

Field Density

Torque Density

Flux Density

A

Flux Density

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13
Q

If an object is magnetically saturated, increasing the external magnetic field will have no further effect on the object. True or False?

True

False

A

True

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14
Q

Potential biologic effects of the static magnetic field include all the following except:

Magnetophosphenes

Peripheral nerve stimulation

Magnetohydrodynamic effect

EKG perturbances

Vertigo/dizziness

A

Peripheral nerve stimulation

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15
Q

In viewing a spatial gradient map, there will be no translational forces exerted on an object when:

Behind the 5 G line

Below the patient table

The spatial gradient is at its maximum

There is no change in the strength of the main static magnetic field- Like at isocenter

A

There is no change in the strength of the main static magnetic field- Like at isocenter

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16
Q

How does shielding within the magnet housing affect the system spatial gradient?

it doesn’t, a system’s SG is the same shielded or unshielded

it increases the system SG because it decreases the size of the fringe field, forcing lines of flux closer together

it decreases the SG because the fringe field is smaller

the shielding is in the walls, not in the magnet system

A

it increases the system SG because it decreases the size of the fringe field, forcing lines of flux closer together

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17
Q

What is defined as “A visual representation of the change of the magnetic field strength over distance?”

Spatial gradient map

Gradient map

B0 map

Deposition map

A

Spatial gradient map

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18
Q

What line is regarded as the point in which non-cleared implants and devices cannot cross safely?

5 mT

500 G

0.05 mT

5 G

A

5 G

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19
Q

The static magnetic field has no bioeffects. True or False?

True

False

A

False

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20
Q

What is the purpose of shielding within the magnet housing/bore?

it makes the magnet safer because the fringe field is smaller

it compresses the fringe field, allowing for a shorter distance to the 5 Gauss line

shielding within the magnet housing replaces shielding within the scan room walls

it increases the cost of the system

A

it compresses the fringe field, allowing for a shorter distance to the 5 Gauss line

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21
Q

What phrase describes second level in regards to static magnetic fields?

No undo physiologic effects are associated with the static magnetic fields of these strengths

A potential for harm to a patient exists

There is definite potential for harm to a patient

It is safe to scan the patient at second level only

A

There is definite potential for harm to a patient

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22
Q

Based on the MSG map above, what would be the maximum spatial gradient that the patient’s head might be exposed to in this position while being moved into the bore?

5 T/m

3 T/m

15 T/m

7 T/m

0.5 T/m

A

3 T/m

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23
Q

A 3T system will always have higher magnetic attractive force than a 1T, regardless of magnet format. True or False?

True

False

A

False

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24
Q

Does gravity or the static magnetic field have a greater effect on an implant that shows a deflection angle of 39 degrees?

Gravity

Magnetic Field

Both Equally

A

Gravity

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25
Q

Bioeffects of the static magnetic field are temporary and disappear when the patient is removed from the field. True or False?

True

False

A

True

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26
Q

The maximum Tesla strength that is safe for infants younger than one month per the FDA is:

8T

1T

4T

1.5T

A

4T

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27
Q

Spatial gradient map values are typically measured in _______ or ________.

mT/Kg or J/cm

W/Kg or J/cm

G/Kg or W/cm

T/m or G/cm

A

T/m or G/cm

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28
Q

Lenz forces are more likely to be experienced by electrically conductive material oriented _______ the static magnetic field.

through

parallel to

perpendicular to

diagonally through

A

perpendicular to

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29
Q

During MR safety testing, an implant demonstrates a deflection angle of 45 degrees. Based solely on this information, the implant would be labeled _____.

MR Safe

MRI Compatible

MR Unsafe

MR Conditional

A

MR Unsafe

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30
Q

Please convert 100 mT to Gauss

1 G

10 G

100 G

1000 G

A

1000 G

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31
Q

The maximum Tesla strength that is safe for adults, adolescents, and infants older than one month per the FDA is:

3 Tesla

7 Tesla

8 Tesla

10 Tesla

A

8 Tesla

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32
Q

Which of the following is NOT a possible bioeffect caused by the static magnetic field?

Magnetophosphenes (flashes of light)

Induced voltages within patient tissues

Nystagmus (repetitive, uncontrolled eye movements)

Vertigo (inner ear effects)

A

Nystagmus (repetitive, uncontrolled eye movements)

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33
Q

Which object would experience the most translational force when exposed to the static magnetic field?

1 kg spherical object

1 kg elongated object oriented parallel to the static magnetic field

1 kg elongated object oriented perpendicular to the static magnetic field

1 kg wire wound into a tight ball

A

1 kg elongated object oriented parallel to the static magnetic field

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34
Q

Translational (missile) force is affected only by the spatial gradient of the static magnetic field. True or False?

True

False

A

True

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35
Q

In horizontal bore scanners, where will the translational force exerted on a metallic object the greatest?

Isocenter

Entrance to Zone 4

Mouth of the bore

Wall of the bore

A

Mouth of the bore

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36
Q

What possible effects can static magnetic fields have on active implants?

Attractive force, focal heating, induced voltages

Attractive force, affect implant functionality, displacement of implant

PNS, rotational force, translational force

False feedback, affect implant functionality, torque

A

Attractive force, affect implant functionality, displacement of implant

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37
Q

Fringe fields are typically either measured in ___________ or ___________, depending on the part of the world.

Gauss / Joules

MilliTesla / Joules

Gauss / milliTesla

Watts / decibels

Gauss / Tesla

A

Gauss / milliTesla

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38
Q

Lenz’s forces are exhibited when a large conductive object moves through the field while oriented perpendicular to the main magnetic field. True or False?

True

False

A

True

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39
Q

What static magnetic field scanning level would result in “No undo physiologic effects” to the patient?

Normal Mode

First Level Mode

Second Level Mode

MR Safe Mode

A

Normal Mode

40
Q

Maximum spatial gradient is proportional to static magnetic field strength, in that higher field strength systems will always have higher MSG. True or False?

True

False

41
Q

A patient complains of a pulling sensation in the area of their implant while they are being advanced into the bore. The sensation goes away when the table motion is stopped. The pulling sensation is due to:

Translational forces of the static magnetic field

Lenz forces caused by the implant moving through the lines of flux

The patient’s imagination

It doesn’t matter because the exam should be cancelled

A

Lenz forces caused by the implant moving through the lines of flux

42
Q

The size and shape of a metallic object will affect its potential projectile effect within the magnetic field. True or False?

True

False

43
Q

The spatial gradient of the static magnetic field is consistent throughout the entire fringe field. True or False?

True

False

44
Q

Magnetophosphenes are more easily produced in higher static field strength systems. True or False?

True

False

45
Q

All of the following are true for spatial gradient maps EXCEPT:

Measured in T/m

May vary in appearance depending on the manufacturer

Visual representation of the change of the magnetic field strength over distance

Visual way of telling the field strength of a static magnetic field

A

Visual way of telling the field strength of a static magnetic field

46
Q

The potential biologic effects of the static magnetic field are thought to be harmful and irreversible. True or False?

True

False

47
Q

The patient may be exposed to magnetic lines of flux upon entering zone 4. True or False?

True

False

48
Q

t is possible for a vertical field open system to have a higher magnetic attractive force than a 3T system. True or False?

True

False

49
Q

Pure aluminum and titanium do not have any interactions with the static magnetic field. True or False?

True

False

50
Q

During MR safety testing, an implant demonstrates a deflection angle of 25 degrees. Based only on this information, the implant would be labeled _______.

MR Safe

MR Conditional

MR Unsafe

MRI Compatible

A

MR Conditional

51
Q

Bioeffects of the static magnetic field are permanent. True or False?

True

False

52
Q

What is 5 Gauss converted to milliTesla?

0.5 mT

0.05 mT

50 mT

500 mT

5000 mT

53
Q

A way to demonstrate Lenz’s forces is:

Walk toward the bore with a pen in your pocket

Throw your keys toward the magnet from the scan room door

Walk toward the magnet while holding a large aluminum object oriented perpendicular to the main magnetic field

Quench the magnet and see what happens

A

Walk toward the magnet while holding a large aluminum object oriented perpendicular to the main magnetic field

54
Q

Implants that have a ________ will try to align ____________ to the direction of the main static magnetic field.

short axis / perpendicular

long axis / perpendicular

long axis / parallel

A

long axis / parallel

55
Q

Which deflection angle(s) would constitute an MR Safe implant?

0 degrees

15 degrees

30 degrees

44 degrees

56
Q

Conductive, nonmagnetic implants/objects will not experience Lenz forces as they move through the static magnetic field. True or False?

True

False

57
Q

For the magnet diagram shown here, approximately how far from isocenter (in the Z-direction) lies the “pacemaker line” where there is the concern that the static magnetic field could potentially interfere with active implanted medical devices?

1 meter

2.5 meters

3.5 meters

4 meters

58
Q

If you are scanning on a 1.5T scanner, this means that a static magnetic field strength of 1.5T is the maximum a patient will encounter within zone 4. True or False?

True

False

59
Q

Force product is the product of:

The strength of the static magnetic field and the spatial gradient of the static field

The RF field and the slope of the time varying gradients

The weight of the magnet and the length of the bore

The length of the body coil and the gradient slew rate

A

The strength of the static magnetic field and the spatial gradient of the static field

60
Q

Which factor will NOT affect the strength of Lenz forces on an object?

Speed of an objects entry into the bore

Object’s electrical conductivity

Cross-sectional size of object

Spatial gradient

Deflection angle of object

A

Spatial gradient

61
Q

The translational force exerted on an object in the magnetic field will be constant throughout the field. True or False?

True

False

62
Q

A surgical clip with a long axis oriented in the head to foot direction will experience a __________ force and align ___________ to the magnetic lines of flux when placed into a vertical field / open MRI.

rotational (torque) / parallel

translational / parallel

rotational / perpendicular

translational / perpendicular

A

rotational (torque) / parallel

63
Q

It is possible for magnetic lines of flux to extend through:

Floors

Walls

Ceilings

Floors and walls

Ceilings and walls

All of the above

A

Floors

Walls

Ceilings

Floors and walls

Ceilings and walls

All of the above

64
Q

Does the shape of an implant or device affect the translational force exerted on the implant/device by the static magnetic field?

Yes

No

65
Q

For the electromagnetic fields used during MR imaging, which is of concern beyond the volume of the bore?

Static magnetic field

Gradient magnetic field

Radiofrequency magnetic field

A

Static magnetic field

66
Q

5 Gauss translates into _______ mT.

5 mT

0.5 mT

0.005 mT

50 mT

0.05 mT

67
Q

0.35 mT translates into _______ G.

35 G

3.5 G

0.035 G

350 G

68
Q

The torque force exerted on an object is a function of:

The magnetic spatial gradient

The strength of the static magnetic field

The gradient slew rate

The length of time is has been exposed to the magnetic field

A

The strength of the static magnetic field

69
Q

Which effects/forces would be exerted on a metallic object as it enters the bore of the magnet?

Lenz, Translational, Induced Voltage

Lenz, Rotational, Translational

Translational, Induced Voltage, Rotational

Torque, Heating, Rotational

A

Lenz, Rotational, Translational

70
Q

Translational (missile) force is affected by which field?

Strength of the static magnetic field

Radiofrequency field

Spatial gradient of the static magnetic field

Slope of the time varying gradients

A

Spatial gradient of the static magnetic field

71
Q

Ferromagnetic materials do not exhibit Lenz effects. True or False ?

True

False

72
Q

Which deflection angles (without sufficient anchoring forces) would constitute an MR Conditional implant?

1-44 degrees

15-45 degrees

30-65 degrees

46-90 degrees

A

1-44 degrees

73
Q

During MR safety testing, an implant demonstrates no deflection. Based solely on this information, the implant would be labeled _____.

MR Conditional

MR Safe

MR Unsafe

The implant cannot be labeled because we do not have enough information

A

The implant cannot be labeled because we do not have enough information

74
Q

What static magnetic field level mode would a 9T MRI Scanner fall under?

Normal Mode

First Level Mode

Second Level Mode

MR Safe Mode

A

Second Level Mode

75
Q

A patient is known to be free of metallic implants/devices. Possible interactions between the patient and the static magnetic field could be:

Claustrophobia

Nothing, The patient is metal-free and will therefore have no interaction with the static magnetic field

Dizziness, nystagmus, altered EKG

Hearing loss

A

Dizziness, nystagmus, altered EKG

76
Q

It is impossible for non-magnetic metals to interact with the static magnetic field. True or False?

True

False

77
Q

What factor does NOT directly contribute to Lenz effects?

Conductivity

Cross-sectional area

Speed of motion

Magnetic field strength

Spatial gradient though which the object is moving

A

Magnetic field strength

78
Q

Torque force exerted on an object in the magnetic field will be the greatest as the object enters the bore. True or False?

True

False

79
Q

What is referred to as “stray lines of magnetic flux that extend outside the bore of the MRI scanner”?

Magnetophosphenes

Fringe field

Flux density

Shielding

A

Fringe field

80
Q

What would be an example of first level in respect to static magnetic field strength?

0.2T

1.0 T

3.0 T

7.0 T

9.0 T

81
Q

If the patient is feet first, supine, what spatial gradient will the head be exposed to at approximately 1.5 meters from isocenter?

approx 5 T/m

approx 3 T/m

approx 1 T/m

approx 0.7 T/m

approx 0.5 T/m

A

approx 0.5 T/m

82
Q

_______________ is when an object becomes airborne when exposed to a static magnetic field.

Missile effect

Translational force

Flux effect

Torque effect

A

Missile effect

83
Q

Characteristics of an object that affect its potential projectile effect within a magnetic field include all of these EXCEPT:

Ferromagnetic property/material

Mass

Age

Size/shape

84
Q

Because the static magnetic field is homogeneous at isocenter, translational (missile) forces there are:

Unable to be measured

At their maximum

Zero

Unimportant

85
Q

Within the magnetic field, translational force will be the greatest at ____________ and the least or zero at ___________.

the location of maximum spatial gradient / isocenter

isocenter / end of table

close to the bore walls / edge of body coil

A

the location of maximum spatial gradient / isocenter

86
Q

For most full body MR systems, the homogeneity of the static magnetic field around isocenter is an area the size of:

The entire body coil

A tennis ball

Only isocenter

A basketball

A

A basketball

87
Q

During MR safety testing, a metallic implant demonstrates no deflection. Based on this information, the implant would be labeled _____.

MR Safe

MR Unsafe

MR Conditional

MR Compatible

A

MR Conditional

88
Q

A paramagnetic object or substance will retain magnetism when removed from the external magnetic field. True or False?

True

False

89
Q

The translational force exerted on an object is a function of:

The strength of the static magnetic field

The magnetic spatial gradient

The gradient slew rate

The length of time it has been exposed to the magnetic field

A

The magnetic spatial gradient

90
Q

A ferromagnetic object or substance will retain magnetism when removed from the external magnetic field. True or False?

True

False

91
Q

The ______ and ________ of an implant is very important in regards to rotational (torque) force.

Size / Shape

Composition / Position

Shape / Position

Size / Position

Composition / Size

92
Q

Deflection testing is performed by:

Placing the object inside a patient then exposing it to the magnetic field

Deciding how the object will behave in the magnetic field by studying its material content

Suspending the object from a string and placing it in the magnetic field

We don’t know, it’s a proprietary process

A

Suspending the object from a string and placing it in the magnetic field

93
Q

Which of the following is NOT a tool / procedure that the technologist should use to avoid a static magnetic field injury?

Ferrous metal detector

5mm gap between patient and bore wall

Screening questionnaire

Verbal interview

A

5mm gap between patient and bore wall

94
Q

What types of materials are most likely to exhibit noticeable Lenz effects?

PVC, Plastics

Aluminum, Brass, Copper

Surgical Steel, Cobalt, Nickel

Gadolinium

A

Aluminum, Brass, Copper

95
Q

Lenz’s forces are harmful and there is no way to mitigate them. True or False?

True

False

MRSO 2 (17 decks)

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