MRSO Test Questions with Complete Solutions.docx

MRSO Test Questions with Complete S physical effects of STATIC FIELDS - Answer-translation rotation lenz physical effects of TIME-VARYING FIELDS - Answer-motion noise induced currents (on object/in person) lenz translation rotation everything NOT MR SAFE needs to be behind... - Answer-5 gauss line earth's magnetic fiels - Answer-0.5 gauss 1.5T = gauss - Answer-15,000 3 T = gauss - Answer-30,000 MR device can be considered non-significant risk IF: (list) - Answer-static mag field SAR dB/dt sound pressure level ^ are below certain threshold dB/dt - Answer-gradient fields rate of change can produce severe discomfort/nerve stimulation limits for# Tesla adults can take - Answer-8T limits for # Tesla a 1month old can take - Answer-4T max unprotected sound level - Answer-140 dB max PROTECTED sound level - Answer-99 dBA biological effects of strong mag fields - Answer-vertigo dizziness nausea magnetohydrodynamic effects induced electric currents... (for time-varying ) magnetophosphenes nerve stimulation/tingling hair static (electric charges on skin) are there known fetal effects of strong magnetic fields? - Answer-nope magnetohydrodynamic effect - Answer-bloodflow changes because blood is flowing inside a strong magnetic field; b/c of ions veering left or right occupational threshold for sound pressure level - Answer-for 8hr shift: 90dB Engineering controls - Answer-eliminate/reduce exposure to hazard through use of engineered structures/machinery/equipment badge access, 4-zone design, shielding around magnet Administrative controls - Answer-eliminate/reduce hazard by modifying/implementing administrative practices visual signs, zone notices, ferrous-free sweeps, MRSO on each shift, floor markings PPE - Answer-ex. hearing protection (headsets, earplugs) MAX TORQUE in a scanner is - Answer-at scanner ISOCENTER MAX TRANSLATIONAL FORCE in a scanner is - Answer-at scanner BORE ENTRANCE how to read static magnetic field map - Answer-move further from bore -- magnetostatic lines are spaced further out higher static magnetic field -- can experience (more/less) torque - Answer- MORE Cryogens: 3 effects? - Answer-explosions asphyxiations frostbite RF heating: 3 effects? - Answer-near field effect resistance ("pinch points") resonance cryogens are... - Answer-supercooled gases... liquid He, N.... Cryogen explosions - Answer-occur when pressure release valve malfunctions regular air can get in container; water vapor can freeze solid over valves -- causes pressure buildup Cryogen asphyxiation - Answer-cryogens escaping into scanner room can CROWD out oxygen -- rapid breathing, impaired coordination, impaired alertness, depression of senses Cryogen frostbite - Answer-=cold burns can cause tissue damage, lung damage if inhaled, change of skin color, blistering how to stay safe with cryogens - Answer-oxygen monitor, quench vents, hammer, door open outward, kick-out panels; check quench vents, quench drills, cryogen level monitoring How does RF heating happen? - Answer-magnetic field component of an RF wave is what we blame for RF heating, not electric field component. but... electric fields in body induces currents... resistance to electric flow deposits heat... *** -- a changing magnetic field (such as that in a RF wave) induces an electric current. this electric current can cause heating and other disturbances (nerve stimulation, etc.) B1 - Answer-time-varying RF fields... RF power... near-field effect - Answer-(a mechanism for RF heating) "contact" with RF coil/antenna near field = region where there are strong effects from currents/charges in the antenna that cause electromagnetic components that don't behave like far-field radiation ...most pulse sequences use the transmit body coil for RF excitation. so avoid contact w scanner bore resistance - Answer-(a mechanism for RF heating) electrical "pinch points" 1) mag field induces electric current in body 2) electrons start flowing in circuit 3) electrons get into electron traffic jam 4) heating! conductive loops generated by the electric fields can encounter "pinch points" that have lots of resistance... = charge buildup at pinch points (i.e., points of contact; between thighs, hand/finger contact, etc.) resonance???? - Answer-(a mechanism for RF heating)