• Object ID: 00000018WIA309EE870GYZ
  • Topic ID: id_40026969 Version: 1.4
  • Date: Aug 20, 2022 11:06:19 AM

GRE scan

GRE is a pulse sequence that reverses gradient polarity to rephase protons and form echoes. Short TRs and flip angles < 90° excite only a portion of the longitudinal magnetization. GRE is available in 2D non-sequential, 3D sequential, and 3D modes. GRE sequences are generally used to create images with T2* contrast.

Figure 1. GRE PSD diagram
Table 1. GRE PSD image legend
NumberDescription
1Variable pulse
2Gradient rephasing pulse
3TE
4TR

Use GRE to acquire T2*-weighted image contrast.

Figure 2. GRE cervical spine images: sagittal (left) and axials (right)
Table 2. Image legend
NumberDescription
1Sagittal cervical spine
2Axial cervical spine

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

  • Scan selections: 2D or 3D Mode, Gradient Echo family, GRE pulse.

General considerations

  • GRE scans are more sensitive to any process that causes T2 dephasing such as B0 inhomogeneities, intravoxel dephasing cancellation due to chemical shift, and magnetic susceptibility effects, which increases as TE increases. Signal voids are seen particularly where there is metal in the body and air/tissue interfaces.
  • As flip angle decreases, SNR decreases. GRE signal reduction requires a surface or extremity coil, more NEX, or 3D mode.
    Figure 3. TR/T1 and Flip Angle Curve
    Table 3. TR/T1 and Flip Angle Curve image legend
    NumberDescription
    1Signal in 0.2 increments
    2TR in 500 ms increments

Scan parameters

  • TR/Flip angle: 2D sequential or 3D mode: keep the TR and flip angle within 10 points of one another to produce the optimum SNR.
  • TE: The TE value determines if fat and water are in phase (bright outline at interface) or out of phase (dark outline at interface). Fat and water in and out of phase times:
    • 1.5T = 2.1 ms

2D GRE 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.

3D GRE 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.