• Optima MR450w BASE 1.5T System Service Methods
  • 5690012-2EN Revision 3
  • Object ID: 00000018WHA30C772GYZ
  • Topic ID: id_2001626 Version: 7.0
  • Date: Feb 21, 2021 9:03:51 PM

Running LVShim in Manual mode

About this task

Procedure

  1. Start the LVShim tool:
    • (For non-proprietary mode) From the Common Service Desktop, select Calibration > LVShim, then select Click here to start this tool.
    By default, Gradshim is performed in auto mode, though manual mode is also available.
  2. Select the shim type (gradient, or test) and Manual Mode, then click Scan.
    Figure 1. LVShim - manual mode
    Note: The gradient shim bit resolution was increased by 16 times. This will result in gradient current values that are much higher than those observed in previous versions of this tool.

    Result

    After the scan is complete, the tool calculates harmonics and compares X, Y and Z to specifications.
    • Green cell = Passed specification
    • Red cell = Failed specification
    Figure 2. Gradient harmonics and gradient bits

    The tool calculates the X, Y and Z gradient delta currents (for gradient bits only) and the new currents based on the harmonics in another window.

    Figure 3. Original delta and new currents (examples)
  3. To accept or decline the new currents:
    • If X/Y/Z harmonics data cells are green, decline the new currents by clicking the Cancel button. Ignore cells with the specification NA.
    • If any harmonics data cells are red, accept the new currents by clicking the Dial In Currents button. The new currents will load in a new column in the LVShim user interface as shown in the Gradient harmonics and gradient bits figure above.
    If after five manual iterations any cell is still red, click More Actions and select Expert Mode.
  4. For more details about the scan (cal file name, center frequency, etc.), select More Actions > More Info.
    Figure 4. More information on scan
  5. When all iterations are complete and all harmonics are within specification, click Exit in the LVShim window.

    If this also fails, run passive shim using the instructions in the applicable Magnet and Cryogens Subsystem Manual.

Finalization

  1. To finalize this procedure, remove any phantoms and/or tools used.
  2. Perform a Check Scan before turning the unit over to the customer. See Doing a check scan.