Question

Using an MRI system involves placing a person in a large superconducting solenoid that can create a magnetic field as large as 3 T. When the imaging process is done, simply switching off the field could induce very large currents in the patient. Estimate the minimum time that we need to ramp down a 3 T field to zero to keep the induced current flowing around a persons torso below 1 mA.

Hint: argue that the loop that matters here is the largest loop around the torso. Therefore, consider a loop about 2 cm thick going around the torso. Conductivity of flesh is about 0.5 ohm^-1m^-1

Answer 1