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MRSO - Static Field - Module 2 Questions with Solutions
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MRSO - Static Field - Module 2
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MRSO - Static Field - Module 2Static field metrics - answer1T = 10,000G
(0.5mT = 5G)
Who published guidelines titled "Criteria for Significant Risk" that specifies what
qualifies as significant risk of exposure to magnetic field associated with MRI. – answer
FDA
FDA guidelines state EXPOSURE to a static field that does not pose a significant risk is:
- answer Limited to 8T for adults and infants > 1 month
Limited to 4T for infants < 1 month
Forces related to static field - answer-Torque/rotation
-Translation/Displacement
-Lenz
magnetic saturation - answer The point where an increase in magnetic force produces
no further magnetic effect in a magnetic material. .
magnetic saturation depends on: - answer-material
-size and shape
-temperature
Most ferromagnetic items are going to saturate at: - answer0.3T - 2.2T
Torque - answerforce exerted on elongated ferromagnetic object so it aligns with the
direction of the magnetic field
Torque will cause an item to align in the _____________ axis in a horizontal field
magnet. - answerz
Torque will cause an item to align in the _____________ axis in a vertical field magnet.
- answery
Torque is dependent on: - answer-length (longer=greater)
-shape (elongated>sperical)
-texture (soft/flexible<hard)(leads/wires<plate)
-location in magnet (greatest at isocenter)
Torque is greatest at - answerisocenter
, Translational / Displacement (missile effect) - answerattractive force on a ferromagnetic
object in a spatial gradient magnetic field
Translational force increases when - answerthe field change over distance increases
(dB/dx)
Spatial gradient magnetic fields are expressed in - answerT/m or G/cm
(1 T/m = 100 G/cm)
Displacement force = - answerB0(dB/dx)
Maximum translational force is at - answerpoint of maximum dB/dx
At isocenter, translation force is - answerzero
Highest spatial gradient for a VERTICAL field system is at - answerpole faces
(item is more likely to attach to sides of poles rather than being drawn toward isocenter)
Where do you obtain a spatial gradient map? - answerSystem vendor
Highest spatial gradient for a HORIZONTAL field system is at - answerentrance to the
bore near the magnet walls
Magnetic shielding is used to - answerreshape/confine the field and bring 5G line into
area of controlled access
Related to the spatial gradient, magnetic shielding can cause - answeran increase in
dB/dx and unpredictability
Shorter bores have higher - answerdB/dx at bore entrance
Lenz's Law - answerThe induced electromagnetic force (emf) gives rise to a current that
flows in a direction so as to set up a magnetic field to oppose the change in magnetic
flux
Not all metal is ferromagnetic, but all metal is - answerconductive
When conductive metal is moved through a magnetic field: - answereddy currents are
induced in the object
Eddy currents induce a - answersecond magnetic field.
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