Echo planar imaging

Echo planar imaging is performed using a pulse sequence in which multiple echoes of different phase steps are acquired using rephasing gradients instead of repeated 180o RF pulses following the 90°/180° in a spin-echo sequence. This is accomplished by rapidly reversing the readout or frequency- encoding gradient. This switching or reversal may also be done in a sinusoidal fashion. Echo planar sequences may use entirely gradient echos or may combine a spin echo with the train of gradient echos as illustrated in the diagram to the right. 

In a single-shot echo planar sequence, the entire range of phase encoding steps,   usually up to 128, are acquired in one TR. In multi-shot echo-planar imaging, the range of phase steps is equally divided into several "shots" or TR periods. For example an image with 256 phase steps could be divided into 4 shots of 64 steps each. 

As a result an image can be acquired in 20-100 msec, allowing excellent temporal resolution such as that required in cardiac imaging. Each subsequent echo results in a progressively T2-weighted signal. 

  • reduced imaging time
  • decreased motion artifact,
  • ability to image rapid physiologic processes of the human body.
  • Sensitive to susceptibility effects
  • Sensitive to main magnetic field inhomogeneity
  • Long gradient echo train causes greater T2* weighting
  • Requires high-performance gradients
  • cardiac imaging
  • abdominal imaging, i.e. breath-hold sequences and 3D MR angiography
  • diffusion imaging
  • perfusion imaging
  • functional imaging
MRI physics
Share article

Article information

rID: 19116
Section: Physics
Tags: epi, mri, refs
Synonyms or Alternate Spellings:
  • Echo-planar imaging
  • Echo planar imaging (EPI)

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    MRI physics diagrams
    Drag here to reorder.
  • Updating… Please wait.

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.