Who produced guidelines named "Criteria for Significant Risk" that define what
constitutes a significant risk of exposure to magnetic fields linked with MRI? -
Response from FDA
According to FDA standards, exposure to a static field that does not pose a major
risk is limited to 8T for people and infants older than one month.
Limited to 4T for newborns under 1 month.
Forces associated to static field - ANSWER: Torque/rotation.
-Translation/Displacement
-Lenz
ANSWER: Magnetic saturation The point at which an increase in magnetic force
creates no more magnetic effect in a magnetic substance.
Magnetic saturation depends on: - ANSWER - material
-Size and Shape
-temperature
, Most ferromagnetic objects will saturate at: - ANSWER: 0.3T -2.2T
Torque is the force applied on an elongated ferromagnetic object so that it aligns
with the direction of the magnetic field.
In a horizontal field magnet, torque causes an item to align along the
_____________ axis. - ANSWER Z
In a vertical field magnet, torque causes an item to align along the _____________
axis. - Answer y.
Torque depends on: - ANSWER - length (longer=greater).
- Shape (elongated>sperical)
- Texture (soft, flexible, or firm) (leads, wires, plate)
-location in magnet (largest at the isocenter).
Torque is greater at the ANSWER isocenter.
Translational or displacement (rocket effect) - ANSWER attracting force on a
ferromagnetic item in a spatial gradient magnetic field
The translational force increases as the field change over distance increases
(dB/dx).
The spatial gradient magnetic fields are given as T/m or G/cm.
(1 T/m equals 100 G/cm)
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