MRSO Exam (Fall 2021) Solved 100%

niobium-titanium - ANSWER-Most commonly used conductor wires. Has critical temperature of 10K (-442F). Liquid Helium is used to cool the wires - cooled to 4K. Field Map - ANSWER-Shows field strength. Greatest at isocenter. 5G Line - ANSWER-0.5 mT. Must be in an area of controlled access. May not be in Zone IV. Spatial Gradient Map - ANSWER-Shows change in field strength over distance (dB/dx) Shielding - ANSWER-Passive: Metal (usually iron) in walls. Active: additional coils in the magnet. Causes a greater change in field strength over distance. Spatial Gradient - ANSWER-dB/dx FIXED magnetic gradient in space. Switched Gradient - ANSWER-dB/dt Within the magnet: additional coils Switch rapidly (polarity) over time. Acoustic noise 3 sets of coil windings Alters phase/frequency during acquisition. Fast switching allows short echo times. Radio Frequency (B1) - ANSWER-Electromagnetic wave Two perpendicular oscillating fields: Electric (E) field Magnetic (B) field RF Characteristics - ANSWER-Frequency: Rate (mH) Calculated by Larmor Equation Depends on nuclei being studied and field strength Higher B0=Higher Frequency Wavelength: Distance between peaks If frequency increases, wavelength decreases Amplitude (power): Height of waves (mT) Lenz's Law - ANSWER-An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.