Echoplanar Pulse Sequences

Echoplanar imaging is a gradient echo technique related to fast gradient echo imaging. Instead of one to 16 phase steps per acquisition TR, the entire set of 64 or 128 phase steps is acquired during one acquisition TR. This is accomplished by rapidly reversing the readout or frequency- encoding gradient. This switching or reversal may also be done in a sinusoidal fashion. Echoplanar sequences may use entirely gradient echos or may combine a spin echo with the train of gradient echos as illustrated in the diagram below. Echoplanar images may be acquired in less that 1/10th of a second and therefore may be useful in cardiac imaging and other rapidly changing processes.