Radiofrequency Flashcards
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
lateral body parts within the transmitting RF coil
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
total accumulated amount of energy deposited into the body per kilogram
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 female who is 8 months pregnant
Increasing echo train length will have what effect on SAR?
Increase
Decrease
No Effect
Increase
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
True
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
Inversely related to the magnetic field - as the field strength increases, the length of concern becomes shorter
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
Total RF delivered over time
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
Reflective energy burns
When assessing risk associated with RF, the primary concern in regards to system hardware is:
table location
receive coil
transmit coil
gantry size
transmit coil
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
40 W/Kg
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
Switching from GRE to FSE based pulse sequences
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
B1+rms
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
rate at which energy is deposited in the body for each scan
SAR is measured in:
J/Kg
W/Kg
mT/M
b1+rms
db/dt
W/Kg
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
False
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.
The fetus will receive little to no RF, so the scan can be performed as normal.
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
2 W/kg / less than
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
True
In regards to safety, we are concerned with _________ when it comes to delivered RF
Hearing loss
Heating
Induced voltages
Torque force
Translational force
Heating
The unit that we use to measure accumulated RF energy deposition is the Joule. True or False?
True
False
True
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
Energy absorbed by the patient/transmitted energy
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
Proximity burns
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
Reflective energy burns
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
it is calculated differently based on the equipment vendor
Keeping all other parameters the same, decreasing the FOV will decrease the amount of RF delivered to the patient. True or False?
True
False
False
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
14,400 J/kg
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
Echo Time TE
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
Surface to volume ratio
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
Whole Body SAR
SED (Specific Energy Dose) is decreased by pausing between scans to allow the patient to cool. True or False?
True
False
False
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
Conditional at 1.5T or 3T
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
Radiofrequency magnetic field
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
35 yrs 300 lb/136 Kg, 172 cm
SAR is calculated identically across all vendors and MRI scanners. True or False?
True
False
False
The radiofrequency magnetic field extends outside the bore and into the scan room during imaging. True or False?
True
False
False
B1+rms is a known measurement based on the pulse sequence and imaging parameters. True or False?
True
False
True
The unit of measure for SAR is ________ while the unit of measure for SED is ________.
Celcius/Watts
Fahrenheit/Kelvin
W/kg /Joule
Feet/Inches
W/kg /Joule
SED stands for _________ and is measured in Joules/kg.
Specific Energy Dose
Specified Energy Deposition
Specific Energy Deposition
Solid Energy Dose
Specific Energy Dose
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
Feet, Ankles, Lower Legs
It is possible for all these body parts to experience looping burns EXCEPT:
Head to shoulder
Medial calves
Medial thighs
Thumb to lateral thigh
Head to shoulder
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
True
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
Field strength is inversely proportional to conductor’s length likely to experience heating
“SAR” stands for:
Specific Alotted Radiofrequency
Specific Absorption Rate
Specified Absorption Ratio
Sporadic Absorption Rate
Specific Absorption Rate
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
Wire insulated along its length with exposed, uninsulated tips
Wavelength of transmitted RF is independent of the medium through which it is traveling. True or False?
True
False
False
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
All the way around the patient, preventing any contact with the bore
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
4 W/kg /up to
What subcategory of SAR limits pictured here is specific to TR/RX coils only?
Whole body SAR
Partial body SAR
Head SAR
Local SAR
Local SAR
SAR and SED describe the same thing. True or False?
True
False
False
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
Diffuse and focal heating
It is possible for induced e-fields and voltage pathways to extend beyond the area of RF irradiation. True or False?
True
False
True
The precessional frequency of hydrogen at 1.5T is:
63.86 MHz
42.57 MHz
65.86 MHz
44.57 MHz
63.86 MHz
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
0.5 meter
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
False
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.
The length decreases as the field strength increases
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
Tx/Rx Knee Coil
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
4T
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
Tx/Rx knee coil
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
25%
Resonant circuitry burns can occur at any field strength: True or False?
True
False
True
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
KJ/Kg or J/Kg / total RF energy delivered by the MRI scanner
Which of the following is NOT a possible RF injury?
Looping
Magnetophosphenes
Proximity
Resonant circuitry
Magnetophosphenes
__________ is measured consistently across all MRI manufacturers.
SAR
Gradient amplitude
SED
B1+rms
B1+rms
From an RF safety perspective, we really don’t care about what receive-only coils are in use. True or False?
True
False
True
Which sequence will have the greatest RF deposition?
Spin Echo
Fast Spin Echo
Gradient Echo
Echo Planar
Fast Spin Echo
The precessional frequency of hydrogen at 7T is:
227.71 MHz
267.71 MHz
291.99 MHz
297.99 MHz
297.99 MHz
SAR and B1+rms are both measurements of energy. True or False?
True
False
True
Will the patient be receiving radiofrequency while within the MRI scanner prior to a sequence running?
Yes
No
No
SAR (Specific Absorption Rate) is a precise, known amount and is calculated equally among MR manufacturers. True or False?
True
False
False
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
4 W/kg / exceeding
Decreasing the FOV is an effective way to decrease the RF exposure to the patient. True or False?
True
False
False
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
At 0.6 meters from isocenter, there is approx. .01% of the RF deposition than at isocenter.
What kind of map is this?
Gradient map
RF map
MSG map
B0 map
RF map
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
SAR should be limited to 2W/kg and the total of all scan sequences should not exceed 15 minutes
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
False
Near field/proximity burns resulting from the transmitting body coil are preventable. True or False?
True
False
True
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
Looping (or kissing) burns
Patient heating is directly influenced by all the following EXCEPT:
Patient’s clothing
Ambient temperature
Pulse sequence selection
Flip angle
Patient weight
Patient weight
