component of the magnetic field that is transverse to the main field of an mri system produced by a unit current flowing through the coil letting the magnetic resonance scanner 39 s static magnetic field point in the z direction in vacuum or air the magnetic field b in a specific region surrounding a coil c may be computed using the biot savart law as follows b u03bc 0 ue89e u222b c ue89e uf74c l u00d7 r r ue89e 3 1 where u03bc 0 is the magnetic permeability of free space dl is the length element along the coil and r is the distance vector from the length element to a point x y z with the integral taken over the length of the coil c the voltage across the ends of the entire coil is v ue8a0 t u222b r ue89e u03c1 ue8a0 x y z t ue89e uf74c v u03b3 ue89e u222b r ue89e b u22a5 c ue8a0 x y z ue89e u03c3 ue8a0 x y z t ue89e uf74c v 2 with the integral taken over a region r containing the molecules which produce a signal contribution u03c1 the signal contribution p from location x y z is observed as where u03b2.