View larger version (44K)

Figure 14. A series of equally spaced RF pulses produces spin echoes that form at the time of subsequent echoes. Once a steady state is reached, signal is produced prior to the excitation pulse, which is echo reformation, and following the excitation pulse, which is a combination of echo and free induction decay. Images can be produced from either the preexcitation signal (S^-) or from the postexcitation signal (S⁺).