Spin-Echo Decay of Spins Diffusing in a Bounded Region

An approximate expression for the spin-echo-decay envelope is obtained from Torrey's equation for spins diffusing in a magnetic field gradient G and in a region that is small compared with (D/γG)^1/3 in the direction of the large uniform magnetic field, and large in the directions perpendicular to the field. (Here D is the diffusion constant and γ the nuclear gyromagnetic ratio.) In a preceding paper, Wayne and Cotts compare this expression with experiment for regions that are large compared with (D/γG)^1/3 but small enough that the simple spin-echo-decay envelope for an infinitely large region does not apply.