• Object ID: 00000018WIA30F59870GYZ
  • Topic ID: id_40021814 Version: 1.5
  • Date: Aug 12, 2022 3:30:48 PM

Fat/Water in Prescan

About this task

Use these steps for the best manual prescanning results when using chemical saturation techniques. This procedure guides you through the process of optimizing Prescan for Fat SAT techniques.
Note: Typically, it is not necessary to use MPS to adjust the CSA and CSF for Spin Echo and Fast Spin Echo sequences. The improved auto prescan that is applied when Fat SAT is turned on in the Scan Parameters area minimizes the need to perform a manual prescan fat/water saturation check.

Step-by-step instructions

  1. In the Workflow Manager control panel, click the Scan arrow > Auto Prescan.
    Figure 1. Scan menu
    • At completion, note the results, especially any accompanying messages referring to CF peak selection.
  2. Click the Scan arrow > Manual Prescan.
  3. From the Manual Prescan screen, click Center Freq Fine (CFH).
    • When performing Fat SAT, make sure CF is set to water.
    • When performing Water SAT, make sure CF is set to fat.
  4. Click Options > Modify RSP to view the Display RSPs screen.
    Figure 2. Display RSPs screen
  5. To visualize the fat and water peaks, in the RSP Name text box type showfp and verify that the Current Value is 1 (on) or showing the fat peak.
  6. Click Accept.
  7. View the spectrum.
    • If the water peak is centered, skip to the next step.
    • If not, adjust the Delta Freq value until the water peak is centered over the vertical line.
    • Use the fat peak as a reference point to confirm that the center frequency is set on water.
    • The water peak should be .
    • If all you want to do is check and adjust the center frequency, then when finished with this step click Done and proceed to scan.
    • If you want to adjust the pulse to better suppress the fat peak, go to the next step.
  8. Click Options > Modify RSP.
  9. In the RSP Name text box type cstun and change the Current Value from 0 to 1.
    • 1 turns on the presaturation pulse that is used for suppressing either fat or water.
  10. Click Accept.
  11. Look at the spectrum to see if the peak you are trying to suppress is gone.
    • If it no longer appears, you can leave the program.
    • If a peak appears, do the following:
      1. In the RSP Name text box type csa and press Enter.
        • CSA is a program that allows you to adjust the amplitude of the suppression pulse. Increasing the amplitude of the pulse may decrease the peak.
      2. Select the existing value, press Delete, and type in a new value 5 to 10 units higher or lower than the defaulted value.
      3. Click Accept.
      4. Repeat these steps until you see the smallest peak.
        Figure 3. Poor fat saturation
        Figure 4. Better fat saturation
        Figure 5. Fat peak sufficiently suppressed
  12. Click Done when you are satisfied with the results.