Patients undergoing an MRI occasionally report seeing flashes of light. Some pra
ID: 1551661 • Letter: P
Question
Patients undergoing an MRI occasionally report seeing flashes of light. Some practitioners assume that this results from electric stimulation of the eye by the emf induced by the rapidly changing fields of an MRI solenoid. We can do a quick calculation to see if this is a reasonable assumption. The human eyeball has a diameter of approximately 24 mm . Rapid changes in current in an MRI solenoid can produce rapid changes in field, with B/t as large as 44 T/s .
What emf would this induce in a loop circling the eyeball?
Explanation / Answer
emf would this induce in a loop circling the eyeball
= /t
= A*B/t
= *r^2*B/t
= *(12x10^-3m)^2*44 = 1.99x10^-2V
= 19.9mV