• Object ID: 00000018WIA30A6C870GYZ
  • Topic ID: id_40023773 Version: 1.4
  • Date: Aug 19, 2022 2:25:29 PM

Spin Echo EPI

EPI uses multiple oscillating gradient “pulses” within a TR period, rather than RF to create the echo. A SE EPI protocol produces contrast similar to a standard SE image with the same TR and TE.

Figure 1. IR EPI PSD

SE EPI is typically used to acquire T2-weighted scans. It can also be combined with the IR Prepared Imaging Option to acquire T1-weighted or IR images.

Figure 2. Spin Echo (T2-weighted) EPI brain (20 slices acquired in 45 seconds)

Consider this information when modifying Spin Echo EPI scan parameters. For specific scan parameter values, select a protocol from your GE or Site library.

  • Scan selections: 2D Mode, Echo Planar Imaging family, Spin Echo EPI pulse.

Spin Echo EPI applications include:

  • Acquiring very fast T2 (SE-EPI) contrast when short scan time is imperative; e.g., to minimize breathing motion, or motion from patients that cannot hold still.
  • Imaging pathologies that cause disruptions in the local magnetic field because they have a higher potential for contrast visualization with EPI sequences.
  • Cardiac imaging for single-slice multi-phase cardiac image without using gating. A single shot acquisition images at a single location over a period of a few seconds.
  • Single or multi-slice multi-phase using cardiac gating taken within a single breath hold.
  • Acquiring very fast T1-weighted images by adding IR Prep, using a long TR (2000 ms), a TI to produce T1 contrast (to 800 ms), and a short TE. These images have a fat suppression appearance due to the spectral fat suppression technique and are typically used in head and extremity imaging.

General considerations

  • Up to 10,000 images can be acquired within a single EPI multi-phase series.
  • There are two EPI type-in PSDs compatible with SE EPI and GRE EPI. For details, see Gradient Echo EPI.
  • When using the head coil, axial, axial oblique, coronal, and coronal oblique, planes automatically have the phase and frequency swapped, in comparison to non-EPI scans. This is to lessen the presentation of geometric distortion and to reduce the potential for peripheral nerve stimulation.

Scan parameters

  • Bandwidth: As the RBw increases, SNR decreases, chemical shift artifact decreases, minimum TE decreases (which means the ESP decreases). As ESP decreases, geometric distortion decreases.
    • 64 kHz is used with 4 to 8 shots.
    • RBw > 64 kHz depends on balancing ESP and resolution demands.
    • Single-shot EPI uses the largest RBw possible.
  • FOV: Large FOVs decrease resolution, increase SNR, and decrease echo space.
  • Frequency: As the frequency matrix increases, the ESP increases.
    • The shortest possible ESP is desirable for a single shot acquisition. Therefore, as the # of shots decreases, consider increasing the FOV.
    • Typically on a single-shot, keep the frequency matrix as low as possible to keep the ESP as short as possible. Finding the right balance between ESP and resolution is critical.
    • Typically a 256 frequency matrix is used with 8 shots or more and RBw 32 to 64 kHz. For 512 frequency matrix, increase the shots and RBw.
  • Phase: As phase matrix increases, the resolution increases, and the # of slices decreases, but the scan time does not change, (scan time = shots × TR). An EPI protocol is the only instance where phase may be larger than the frequency value.
  • Phase Correct: Always select Phase Correct with EPI scans so that the system can run a “reference” scan prior to data acquisition.
    • If a 1 NEX acquisition is programmed, the reference scan can take as long as the EPI scan, but it is imperative to run Phase Correct in order to have optimum image quality.
    • The reference scan automatically occurs after a successful prescan. It makes calculations and corrections for placing the echo underneath the frequency gradient.
  • Phase FOV: As PFOV decreases, geometric distortion decreases.
  • Shots: As the number of shots increase, the susceptibility artifacts decrease, and the scan time increases.

Imaging Options

  • IR-Prepared: Select it for either an IR, T1-weighted, or STIR contrast image.

User CVs

Click the Advance tab to view the available User CVs. The CVs may vary based on the field strength and selected scan and imaging parameters.

Post-process tasks

For details, see Add post-process task. Compatible post-process tasks include:

  • Image Enhancement Filters
  • Negative Enhancement Integral: MRSTD with Multi-Phase and fMRI Imaging Options