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MRSO 2 > Radiofrequency > Flashcards

Radiofrequency Flashcards

1
Q

The most common locations of proximity burns are:

lateral body parts within the transmitting RF coil

medial body parts within the transmitting RF coil

lateral body parts within the receiving RF coil

medial body parts within the receiving RF coil

A

lateral body parts within the transmitting RF coil

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2
Q

SED (Specific Energy Dose) is the:

rate at which energy is deposited into the body during each scan

total accumulated amount of energy deposited into the body per kilogram

amount of heat generated during scanning

measurement of temperature increase in the body

A

total accumulated amount of energy deposited into the body per kilogram

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3
Q

Which of these patients would be more likely to experience RF related heating during scanning?

An infant weighing 7 lb 4 oz

A female who is 8 months pregnant

A male weighing 175 lb and 5 ft 11 in tall

A 2 year old child weighing 26 pounds and 33in tall

A

A female who is 8 months pregnant

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4
Q

Increasing echo train length will have what effect on SAR?

Increase

Decrease

No Effect

A

Increase

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5
Q

Resonant circuitry related heating is only a concern if the implant or device is in the area of RF deposition. True or False?

True

False

A

True

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6
Q

The length of concern for resonant frequency heating of a conductor is:

Directly related to the magnetic field - as the field strength increases, the length of concern becomes longer

Inversely related to the magnetic field - as the field strength increases, the length of concern becomes shorter

It doesn’t matter - all conductors are a concern no matter their length

A

Inversely related to the magnetic field - as the field strength increases, the length of concern becomes shorter

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7
Q

B1+rms is a way of measuring:

RF absorption

A calculated RF deposition model

Gradient strength

Total RF delivered over time

The total translational attraction of an object

A

Total RF delivered over time

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8
Q

What injury is caused by certain materials that retain concentrated ambient energies, which can cause focal heating and burns?

Reflective energy burns

Proximity burns

Resonant circuitry burns

Looping burns

A

Reflective energy burns

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9
Q

When assessing risk associated with RF, the primary concern in regards to system hardware is:

table location

receive coil

transmit coil

gantry size

A

transmit coil

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10
Q

Which value listed below represents the SAR limits of knee using a TX/RX coil within first level controlled mode?

2 W/Kg

20 W/Kg

10 W/Kg

40 W/Kg

3.2 W/Kg

A

40 W/Kg

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11
Q

All of these are possible ways to reduce patient warming except:

Removing blankets

Turning on the fan within the bore

Switching from GRE to FSE based pulse sequences

Entering the correct patient weight

A

Switching from GRE to FSE based pulse sequences

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12
Q

What is a mathematical method of calculating the total RF delivered within a sequence in a sine wave that varies across time and calculating an average measurement?

SED

B1+rms

SAR

Transmit Bandwidth

A

B1+rms

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13
Q

SAR (Specific Absorption Rate) is the:

total accumulated amount of energy deposited in the body

amount of heat generated during scanning

rate at which energy is deposited in the body for each scan

measurement of the body temperature rise during scanning

A

rate at which energy is deposited in the body for each scan

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14
Q

SAR is measured in:

J/Kg

W/Kg

mT/M

b1+rms

db/dt

A

W/Kg

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15
Q

SAR and B1+rms are like inches and centimeters, they’re measuring the exact same thing, just on different scales. True or False?

True

False

A

False

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16
Q

A pregnant patient needs an MRI of the brain that will be performed with a transmit/receive head coil. Which statement will be true in regards to the RF delivery to the fetus?

All RF will be absorbed by the abdominal tissues before reaching the fetus

The fetus will be exposed to a large amount of RF, but because the radiation is non-ionizing, the scan should be performed as normal.

The fetus will receive little to no RF, so the scan can be performed as normal.

The fetus will receive RF, but it will depend on the trimester that the patient is in. That will make the difference whether we can scan the pregnant mother.

A

The fetus will receive little to no RF, so the scan can be performed as normal.

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17
Q

Normal mode in regards to whole body RF deposition does not exceed _________ and will result in a body temperature change of ________ 1 degree Celsius.

4 W/kg / up to

3.2 W/kg / above

2 W/kg / up to

2 W/kg / less than

A

2 W/kg / less than

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18
Q

The amount of allowable SAR to the head while using a RX only coil does not change between normal and first level operating modes. True or False?

True

False

A

True

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19
Q

In regards to safety, we are concerned with _________ when it comes to delivered RF

Hearing loss

Heating

Induced voltages

Torque force

Translational force

A

Heating

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20
Q

The unit that we use to measure accumulated RF energy deposition is the Joule. True or False?

True

False

A

True

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21
Q

SAR is a measurement of ______ while B1+rms is a measurement of _______.

Time/space

Heat/heat

Energy absorbed by the patient/transmitted energy

It doesn’t matter because the system does the calculations

A

Energy absorbed by the patient/transmitted energy

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22
Q

What kind of RF injury is caused by the body part in question being too close to the transmitting RF source?

Looping burns

Reflective energy

Resonant circuitry

Proximity burns

A

Proximity burns

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23
Q

What kind of RF injury is due to certain materials that can concentrate ambient energies into smaller volumes, potentially causing focal heating and or burns?

Resonant circuitry burns

Looping burns

Reflective energy burns

Proximity burns

A

Reflective energy burns

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24
Q

All of the following are true about B1+rms EXCEPT:

it is a more precise measurement of RF exposure than SAR

it is a known quantity, not an estimated value

it is calibrated by the system hardware during prep/prescan

it is calculated differently based on the equipment vendor

A

it is calculated differently based on the equipment vendor

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25
Q

Keeping all other parameters the same, decreasing the FOV will decrease the amount of RF delivered to the patient. True or False?

True

False

A

False

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26
Q

On some newer MRI systems, a maximum SED dose of _________ is allowed to be delivered to each patient per 24 hour period.

14,000 J/kg

14,400 J/kg

9000 J/kg

6000 J/kg

6,600 J/kg

A

14,400 J/kg

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27
Q

Which scan parameter shown here does not affect SAR?

Repetition Time TR

Echo Time TE

Echo Train length

Number of Signal Averages

Number of Phase Encoding Steps

A

Echo Time TE

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28
Q

A patient’s ability to dissipate heat is directly related to their:

Height and weight

Skin and eye color

Age and ethnicity

Surface to volume ratio

A

Surface to volume ratio

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29
Q

Which SAR category represents the deposited SAR values to the tissues within the transmitting body coil averaged over the total mass of the patient?

Whole Body SAR

Partial Body SAR

Head SAR

Local SAR

A

Whole Body SAR

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30
Q

SED (Specific Energy Dose) is decreased by pausing between scans to allow the patient to cool. True or False?

True

False

A

False

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31
Q

Implant/device labeling specific to RF resonance limitations will state:

Conditional up to 3T

Maximum whole body averaged SAR of 2 W/kg for 15 minutes of scanning

Conditional at 1.5T or 3T

Restrictions on local transmit/receive coils

A

Conditional at 1.5T or 3T

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32
Q

Burns are the most commonly reported MR-related adverse event. Which of these electromagnetic fields contributes to these events?

Static magnetic field

Radiofrequency magnetic field

Gradient magnetic field

A

Radiofrequency magnetic field

33
Q

Which patient listed will likely have the hardest time dissipating heat caused by transmitted RF?

5 days, 9lb/4 Kg, 56 cm

35 yrs 300 lb/136 Kg, 172 cm

45 yrs 220 lb/100 Kg, 172 cm

65 yrs, 165 lb/75Kg, 190 cm

A

35 yrs 300 lb/136 Kg, 172 cm

34
Q

SAR is calculated identically across all vendors and MRI scanners. True or False?

True

False

A

False

35
Q

The radiofrequency magnetic field extends outside the bore and into the scan room during imaging. True or False?

True

False

A

False

36
Q

B1+rms is a known measurement based on the pulse sequence and imaging parameters. True or False?

True

False

A

True

37
Q

The unit of measure for SAR is ________ while the unit of measure for SED is ________.

Celcius/Watts

Fahrenheit/Kelvin

W/kg /Joule

Feet/Inches

A

W/kg /Joule

38
Q

SED stands for _________ and is measured in Joules/kg.

Specific Energy Dose

Specified Energy Deposition

Specific Energy Deposition

Solid Energy Dose

A

Specific Energy Dose

39
Q

If a patient is positioned feet first, supine and is being scanned for ankle pain using a receive only ankle coil, which area(s) are likely to receive RF?

Head, Neck, Thorax

Thighs, Pelvis, Abdomen

Feet, Ankles, Lower Legs

Fingers, Wrists, Elbows

A

Feet, Ankles, Lower Legs

40
Q

It is possible for all these body parts to experience looping burns EXCEPT:

Head to shoulder

Medial calves

Medial thighs

Thumb to lateral thigh

A

Head to shoulder

41
Q

If patient tissue/skin contact must be present in the area of transmitted RF, large cross-sectional areas of skin contact is better than light touching or small contact points. True or False?

True

False

A

True

42
Q

ALL of the following are true in regards to resonant circuitry burns EXCEPT:

Resonant circuitry can happen at any field strength

The higher the field strength, the greater the chance of resonant circuitry in long conductors

Occurs when the conductive element has a length corresponding to the RF’s transmitted wavelength

Field strength is inversely proportional to conductor’s length likely to experience heating

A

Field strength is inversely proportional to conductor’s length likely to experience heating

43
Q

“SAR” stands for:

Specific Alotted Radiofrequency

Specific Absorption Rate

Specified Absorption Ratio

Sporadic Absorption Rate

A

Specific Absorption Rate

44
Q

Which of these would be the most concerning for thermal injury due to electrical conduction?

Wire insulated along the entire length with capped tips

Spherical metallic object

Noninsulated wire

Wire insulated along its length with exposed, uninsulated tips

A

Wire insulated along its length with exposed, uninsulated tips

45
Q

Wavelength of transmitted RF is independent of the medium through which it is traveling. True or False?

True

False

A

False

46
Q

It is important to use the manufacturer recommended thickness of padding/air gap between the patient and the bore walls:

Only on the sides between the patient’s arms and the bore

Only where the patient requires padding for comfort

All the way around the patient, preventing any contact with the bore

Anywhere it will fit, otherwise pillowcases and sheets are sufficient

A

All the way around the patient, preventing any contact with the bore

47
Q

First level in regards to RF deposition to the whole body does not exceed _________ and will result in a body temperature change of ________ 1 degree Celsius.

2 W/kg / above

4 W/kg / below

4 W/kg /up to

4 W/kg / above

A

4 W/kg /up to

48
Q

What subcategory of SAR limits pictured here is specific to TR/RX coils only?

Whole body SAR

Partial body SAR

Head SAR

Local SAR

A

Local SAR

49
Q

SAR and SED describe the same thing. True or False?

True

False

A

False

50
Q

Which of the following is a possible bioeffect caused by RF?

Magnetophosphenes

Nystagmus

Induced voltages within patient tissues

Diffuse and focal heating

Peripheral nerve stimulation

A

Diffuse and focal heating

51
Q

It is possible for induced e-fields and voltage pathways to extend beyond the area of RF irradiation. True or False?

True

False

A

True

52
Q

The precessional frequency of hydrogen at 1.5T is:

63.86 MHz

42.57 MHz

65.86 MHz

44.57 MHz

A

63.86 MHz

53
Q

For this MR system, at what spatial distance from isocenter would we no longer need to be concerned about any RF heating to an implant?

0.2 meter

0.4 meter

0.5 meter

0.7 meter

1 meter

A

0.5 meter

54
Q

From an RF safety perspective, it is just as important to know what coil is being used to receive as it is to know which coil is being used to transmit. True or False?

True

False

A

False

55
Q

What is the relationship between the length of a conductor and the static field strength in regards to resonant circuitry heating?

The length increases as the field strength increases

The length decreases as the field strength increases

There is no relationship between length of a conductor and field strength

Heating is caused by RF, so we should not be concerned with the static field.

A

The length decreases as the field strength increases

56
Q

Of the coils listed below, which would deliver the least amount of RF energy to the patient?

Tx/Rx Body Coil

Tx/Rx Knee Coil

Rx Only Head Coil

A

Tx/Rx Knee Coil

57
Q

At what field strength would the risk for an electrical conductor with a length of 10 cm (3.9 inches) to experience resonant circuitry heating be the greatest?

0.2T

1T

1.5T

4T

A

4T

58
Q

Which coil listed would expose the brain the to least amount of radiofrequency if used?

Inherent Tx/Rx Body Coil

Tx/Rx knee coil

Receive Only knee coil

A

Tx/Rx knee coil

59
Q

By decreasing the flip angle from 180 degrees to 90 degrees, the RF energy will be decreased to ______ of the original value.

25%

50%

100%

The root mean square of the sine wave

A

25%

60
Q

Resonant circuitry burns can occur at any field strength: True or False?

True

False

A

True

61
Q

Specific Energy Dose is measured in___________ and measures _________:

KW/Kg or W/Kg / total RF energy delivered by the MRI scanner

KJ/cm or J/cm / sequence specific RF absorption by the patient

KJ/Kg or J/Kg / total RF energy delivered by the MRI scanner

KJ/Kg or J/Kg / sequence specific RF absorption by the patient

A

KJ/Kg or J/Kg / total RF energy delivered by the MRI scanner

62
Q

Which of the following is NOT a possible RF injury?

Looping

Magnetophosphenes

Proximity

Resonant circuitry

A

Magnetophosphenes

63
Q

__________ is measured consistently across all MRI manufacturers.

SAR

Gradient amplitude

SED

B1+rms

A

B1+rms

64
Q

From an RF safety perspective, we really don’t care about what receive-only coils are in use. True or False?

True

False

A

True

65
Q

Which sequence will have the greatest RF deposition?

Spin Echo

Fast Spin Echo

Gradient Echo

Echo Planar

A

Fast Spin Echo

66
Q

The precessional frequency of hydrogen at 7T is:

227.71 MHz

267.71 MHz

291.99 MHz

297.99 MHz

A

297.99 MHz

67
Q

SAR and B1+rms are both measurements of energy. True or False?

True

False

A

True

68
Q

Will the patient be receiving radiofrequency while within the MRI scanner prior to a sequence running?

Yes

No

A

No

69
Q

SAR (Specific Absorption Rate) is a precise, known amount and is calculated equally among MR manufacturers. True or False?

True

False

A

False

70
Q

Second level in regards to RF deposition exceeds _________ and will result in a body temperature change ________ 1 degree Celsius.

4W/kg / below

3.2 W/kg / exceeding

4 W/kg / exceeding

4 W/kg / equal to

A

4 W/kg / exceeding

71
Q

Decreasing the FOV is an effective way to decrease the RF exposure to the patient. True or False?

True

False

A

False

72
Q

Which statement is true in regards to this RF map?

At 0.5 meters from isocenter, there is approx. 50% less RF deposition than at isocenter.

at 0.2 meters from isocenter, there is approx. 90% less RF deposition than at isocenter.

At 0.6 meters from isocenter, there is approx. .01% of the RF deposition than at isocenter.

The RF map has absolute values

A

At 0.6 meters from isocenter, there is approx. .01% of the RF deposition than at isocenter.

73
Q

What kind of map is this?

Gradient map

RF map

MSG map

B0 map

A

RF map

74
Q

An implant MR safety labeling includes “Maximum MR system reported whole-body-averaged specific absorption rate (SAR) of 2-W/kg for 15 minutes of scanning”. What does this mean?

SAR should be limited to 2W/kg, but all scans must be completed within 15 minutes

SAR should be limited to 2W/kg and the total of all scan sequences should not exceed 15 minutes

SAR should be limited to 2W/kg and each sequence should not exceed 15 minutes of continuous scanning

We can’t scan this patient because SAR cannot be limited on our scanner

A

SAR should be limited to 2W/kg and the total of all scan sequences should not exceed 15 minutes

75
Q

It is not possible to know the amount of RF energy that extends beyond the volume of the transmitting RF coil. True or False?

True

False

A

False

76
Q

Near field/proximity burns resulting from the transmitting body coil are preventable. True or False?

True

False

A

True

77
Q

What kind of RF injury is associated with two body parts barely touching and fufills the requirements of Faraday’s law of electromagnetic induction?

Resonant circuitry burns

Looping (or kissing) burns

Reflective burns

Proximity burns

Montgomery burns

A

Looping (or kissing) burns

78
Q

Patient heating is directly influenced by all the following EXCEPT:

Patient’s clothing

Ambient temperature

Pulse sequence selection

Flip angle

Patient weight

A

Patient weight

MRSO 2 (17 decks)

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