• Discovery MR750 3.0T System Service Methods
  • 5690009-2EN Revision 4
  • Object ID: 00000018WIA303C4E50GYZ
  • Topic ID: id_2028142 Version: 2.0
  • Date: Feb 24, 2021 1:18:33 AM

Running LVShim - Gradshim

The objective is to complete fine tuning of the homogeneity of the magnet.

About this task

By default, gradshim is performed in auto mode, although manual mode is also available.

Procedure

  1. Make sure that all coils have been removed from the cradle and phantoms from the bore.
  2. Set up and align the LVShim phantom. Align the phantom so that:
    1. The phantom’s seam is oriented perpendicular to the table.
    2. The phantom’s z-axis is along the length of the cradle.
    3. The phantom is centered left to right with respect to the cradle top.
      Figure 1. Placing the LVShim phantom on the patient table
      Note: This image is a representative example. Actual systems may vary.
  3. Landmark on the LVShim phantom crosshairs.
    Note: The landmarking tolerances of the LVShim tool are: I/S: ± 3 mm, A/P: ± 30 mm, R/L: ± 5 mm. Ensure accuracy of the placement for landmarking.
    Note: Due to the tight landmarking tolerance, it is important to align the lasers on the crosshairs of the LVShim phantom.
  4. Press Advance to Scan.
    Note: The tool checks phantom positioning and will fail if the above landmarking specs are out of tolerance.
  5. Select the gradshim mode:
    OptionDescription
    Auto modeRunning LVShim in Auto mode
    Manual modeRunning LVShim in Manual mode