Dependence of Magnetization Response on Selection Field Offset. Relation between ideal particle response and selection field offset. A constant gradient G is assumed leading to a selection field H
S(x) = Gx. The superposition of selection field H
S(x) and harmonic drive field H
D(t) = A cos ω
t generates a magnetization response M(x, t) which induces a voltage proportional to s(x, t) in the receive coil. Depending on position x, the signal spectrum has a characteristic pattern S
(x). Since the signal s(t) is real and odd, its Fourier components are purely imaginary.