Natural Science Forum / Physics / General Physics / March 2006

If a small piece of diamagnetic material such as graphite is
brought from either end, to a position near the entrance to the
throat of a Magnetic Resonance Imaging (MRI) system it will
experience a force of repulsion, tending to push the graphite
away from the entrance to the MRI throat.

Assuming the MRI field is very linear within the MRI throat, what
diamagnetic force will the graphite experience if it is placed at
or near the mid position inside the MRI throat? Will the
diamagnetic forces acting upon the graphite be parallel to the
magnetic field of the MRI throat and balanced with a net force of
or near zero, or would the force upon the graphite tend to move
it out of the MRI throat?

Next, imagine a plane that is perpendicular to the field within
the MRI throat, and intersecting this field at about the mid
point along the axis of the MRI throat. Now, if the graphite is
placed outside the MRI system, within or near this plane, what
diamagnetic forces will it experience? Will this placement result
in an equal but not oppositely directed pair of forces from each
pole of the MRI throat? If so, will these non-colinear forces
produce a net resultant force tending to move the graphite away
along a radius of this equatorial plane?

If this is right, so far, I am ready to derive the equation(s)
for the force(s) acting on the graphite. Help!!!!!