Real Time Center Frequency

The Real Time Center Frequency option is available with DW-EPI scans, DTI scans (DW-EPI scans with Tensor selected as the Diffusion direction) and 2D FSE Fat SAT scans (2D FSE with Fat Saturation). In DW-EPI and DTI scans, Real Time Center Frequency applies the optimal center frequency for each slice. In 2D FSE Fat SAT scans, when the option selected on, dynamic center frequency and shim will be applied for each prescribed slice to improve fat saturation performance.

The Real Time Center Frequency option is located on the Details tab for DWI and DTI scan prescriptions.

In DW-EPI and DTI scans, it is used in following:

• To improve fat suppression in areas of high B0 inhomogeneity (off-isocenter, or area with high tissue susceptibility).

  

  Table 1. Image legend

  Number	Description
  1	Image acquired with Real Time Center Frequency option turned Off. The arrows indicate the area of poor fat suppression.
  2	Image acquired with Real Time Center Frequency option turned On. Note the improved fat suppression.

• To reduce signal drop-off in areas of high B0 inhomogeneity (off-isocenter, or area with high tissue susceptibility).
• For improved image quality in the neck and shoulder region, and to reduce signal drop off in the spine area, follow this recommendations:
  • Apply one rectangular or two square shim volumes to cover the spinal cord region.

    

    Table 2. Image legend

    Number	Description
    1	Image acquired with Real Time Center Frequency option turned Off. The circle indicates the area of signal drop-off.
    2	Image acquired with Real Time Center Frequency option turned On. Note the reduced signal drop-off.

• To reduce station-to-station misalignment in whole body diffusion imaging.

  

  Table 3. Image legend

  Number	Description
  1	Image acquired with Real Time Center Frequency option turned Off. The circle indicates the area of poor alignment.
  2	Image acquired with Real Time Center Frequency option turned On. Note the improved station-to-station alignment.

Considerations for DWI and DTI

• When Real Time Center Frequency (RTCF) is turned on, the scan time increases by approximately 1 TR (plus 1-2 second for various pulse sequence computation time and wait time). The first TR is used to estimate the center frequencies for each slice.
• Real Time Center Frequency option is not compatible with the following:
  • Focus Excitation Mode
  • DWI and DTI scans with no ASSET Imaging Option and when the FLAIR Inversion User CV is turned On.
  • HyperBand Imaging Option
  • Navigator Imaging Option
  • When non-axial (including non-axial oblique) scan planes are selected
  • Single channel coils such as the Body coil
  • When breast anatomy is selected from Anatomical Region.
• Real Time Center Frequency option is grayed out under the following conditions:
  • IR Prepared Imaging Option is selected or,
  • Fat Sat is selected from the Chem SAT menu on the Scan Parameter screen, and,
  • Enhanced Fat Suppression User CV is set to 0. If you set Enhanced Fat Suppression to 1 or 2, then the Real Time Center Frequency option becomes available.

In 2D FSE Fat SAT scans:

Real Time Center Frequency is only available if a Chemical Saturation Pulse is prescribed in 2D FSE scans. For 2D FSE details, see FSE scan. When the option selected on, Smart Fat Sat(SFS) will be triggered on. SFS can improve fat saturation performance by real-time compensating in-plane B0 inhomogeneity and adjusting Chemical SAT Pulse Center Frequency of each slice:

Table 4. Image legend

Number	Description
1	Image acquired with Smart Fat Sat turned off.
2	Image acquired with Smart Fat Sat turned on.

Considerations for 2D FSE Fat SAT

• Real Time Center Frequency option is located on the Details tab for 2D FSE scan prescriptions.

• Real Time Center Frequency option is only available if a Chemical Saturation Pulse is prescribed.
• When RTCF is turned on, the scan time will increases. The extra time results from the wider Chemical SAT Pulse used in Smart Fat Sat. For Chemical SAT Pulse details, see Prescribe a chemical SAT pulse
• RTCF option is not compatible with the following 2D FSE Fat SAT scans:
  • STIR application.
  • SSFSE application.
  • Non-Chemical SAT application.
  • When spine anatomy is selected from Anatomical Region.
• When RTCF option is turn on and Smart Fat sat is triggered on, local shim is not supported. While, localized Center Frequency Fine(CFH) adjustment is available by placing a single shim volume or two shim volumes. For shim volume details, see Shim volume.
• When turn on RTCF for Neck Anatomical, Smart Fat sat can improve fat-sat performance, while non-fatty tissue may appear shading as a result of local inhomogeneities especially at air/tissue interfaces.