MRSO PREP 212 Questions with Complete Solutions Zero Boil-Off - Correct Answers System that reduces/eliminates the need to recharge Helium in a magnet.Quench - Correct Answers 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 - Correct Answers 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 - Correct Answers Liquid Helium 42* Kelvin Dual Cryogen System - Correct Answers Helium Nitrogen (used to keep Helium cold as back-up) Quench Vent - Correct Answers Used to vent boiled off Helium to the outside.Quench Vent in MRI Room is Zone IV (MRI manufacturer/engineer responsible for inspecting) 1 / 3
Quench Vent outside is Zone III (Facility responsible for inspecting) Quench concerns with malfunctioning Quench Vent. - Correct Answers Dense fog in room.Can rain or snow which can contain Oxygen which is a fire risk.Hypothermia/Frostbite due to lowered room temperature.Aphyxiation 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 - Correct Answers 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 - Correct Answers ICNIRP
- Head and trunk is limited to a magnetic flux
density of 2T
- Limits are limited to a magnetic flux density of
8T 2 / 3
IEC
- Head and trunk is limited to a magnetic flux
- Limbs are limited to a magnetic flux density of
- 80% of the maximum dB/dt exposure.
- / 3
density of 4T.
4T.Static Magnetic Field General Public Exposure Limits - Correct Answers 400mT FDA Limits for Static Magnetic Field - Correct Answers < 1 month old - 4T >1 month old - 8T Exposure to Static Magnetic Field of >4T - Correct Answers Requires approval.Time Varying Gradient Field Concerns - Correct Answers Electrical induction due to principle of Faraday's Law.Cardiac Fibrilation (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 - Correct Answers IEC/FDA Normal Operating Mode