Exam (elaborations)
MRSO PREP QUESTIONS AND ANSWERS
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Exam of 22 pages for the course MRSO at MRSO (MRSO PREP)
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MRSO PREPZero Boil-Off - answer System that reduces/eliminates the need to recharge Helium in a
magnet.
Quench - answer Quickly eliminating the magnetic field.
Not immediate, takes 3 to 5 minutes to completely eliminate magnetic field.
Loud Noise as Helium rushes out of Quench Vent.
Can cause crack in the wire (very costly to repair/replace).
Ohm's Law - answer Resistance that is equal to Voltage divided by the amperage in a
wire.
V=IR
Use of Cryogen reduces/eliminates heating with high voltage and amperage which
allows for high magnetic field.
Cryogen - answer Liquid Helium
42* Kelvin
Dual Cryogen System - answer Helium
Nitrogen (used to keep Helium cold as back-up)
Quench Vent - answer Used to vent boiled off Helium to the outside.
Quench Vent in MRI Room is Zone IV (MRI manufacturer/engineer responsible for
inspecting)
Quench Vent outside is Zone III (Facility responsible for inspecting)
Quench concerns with malfunctioning Quench Vent. - answer Dense fog in room.
Can rain or snow which can contain Oxygen which is a fire risk.
Hypothermia/Frostbite due to lowered room temperature.
,Asphyxiation
Ruptured Ear Drums because of increased pressure in room.
Difficulty opening door to Zone III due to increased pressure. May have to break window
to release pressure.
Magnet doesn't immediately lose its magnetic field.
Peripheral Nerve stimulation due to change in magnetic field.
Static Magnetic Field Concerns - answer Translation/Rotational Force
*No adverse effects to patients or fetus have been noted to individuals exposed to up to
8T.
Static Magnetic Field Occupational Exposure Limits – answer ICNIRP
- Head and trunk is limited to a magnetic flux
density of 2T
- Limits are limited to a magnetic flux density of
8T
IEC
- Head and trunk is limited to a magnetic flux
density of 4T.
- Limbs are limited to a magnetic flux density of
4T.
Static Magnetic Field General Public Exposure Limits - answer400mT
FDA Limits for Static Magnetic Field - answer< 1 month old - 4T
>1 month old - 8T
Exposure to Static Magnetic Field of >4T - answer Requires approval.
Time Varying Gradient Field Concerns - answer Electrical induction due to principle of
Faraday's Law.
Cardiac Fibrillation (not reported).
Diaphragm Spasm - cause difficulty breathing.
, Brain
Peripheral Nerve Stimulation - limited to the comfort of the patient.
Time-Varying Gradient Field Normal Operating Mode Limits – answer IEC/FDA
Normal Operating Mode
- 80% of the maximum dB/dt exposure.
= +1.0 * rb(1+0.36/teff)
Time-Varying Gradient Field First Level Mode Limits – answer IEC/FDA
100% of the maximum dB/dt
= 0.8 *rb(1+0.36/teff)
Time-Varying Gradient Field Occupational Exposure Limits – answer ICNRP
- restrictions are limited to 100kHz
IEC
- Limits to peripheral nerve stimulation.
Time-Varying RF Field Concerns - answer The deposit of Heat (measured in SAR).
Localized Heating to: Eyes, Fetus, & Testicles.
RF Burning.
Time-Varying RF Field Temperature Increase Limits – answer FDA
- Whole body Exposure <1* Celsius.
Time-Varying RF Field Heating Limits Normal Operating Mode - answer Increase in
core temperature to 0.5* Celsius
Increase in whole body SAR to less than 2W/kg
Head SAR less than or equal to 3.2 W/kg
Time-Varying RF Field Heating Limits First Level Mode - answer Increase in core
temperature to 1* Celsius.
Increase in whole body SAR to less than 4W/kg.
Head SAR less than or equal to 3.2 W/kg.
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