- Discovery MR750 3.0T System Service Methods
- 5690009-2EN Revision 4
- 00000018WIA30D42110GYZ
- id_20035086.4
- Oct 11, 2021 6:13:21 PM
Running LVShim Fine
The objective is to further improve and tune the homogeneity as compared to LVShim Rough.
About this task
| DANGER | |
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Potential fatal injury Before beginning this shim procedure, a second person (GE employee or contractor trained in safety requirements) must be present in the area in case of emergency. All work assistants or observers must comply with the Work assistant/observer system requirements and certification subsection of the MR Magnet and Cryogen Manual. | |
Use the three-piece LVShim phantom. The LVShim Fine process is done with a sampling diameter of 45 cm DSV.
Procedure
- On the LVShim user interface, click Scan.Note: To abort the scan, click Abort or press the Stop Scan button on the control panel.Note:
During LVShim procedures, the system performs a Body SPT SNR to verify system integrity. If the Body SPT SNR fails, troubleshoot the SNR issue (in particular, check the I and Q drive cable connections) before continuing with LVShim.
Figure 1. Starting a scan 
Result
After the scan is completed, the tool calculates the harmonics and compares them with the specifications.
- Green cell = Passed specification
- Red cell = Failed specification
Figure 2. Harmonics and specifications comparison 
The tool calculates the delta currents and the new currents, and displays currents in a pop-up dialogue.
Figure 3. Currents displayed 
- Accept or decline the new currents:
- If all harmonics data cells are green, decline the new currents by clicking Cancel.
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If any harmonics data cells are red, click Dial in Currents to accept the new currents.
The new currents will be displayed in a new column in this window. Dial in the currents from the new Loaded Current column using the Supercon Shim power supply. See the applicable Magnet and Cryogens Subsystem Manual for information about dialing in the currents.
Figure 4. Second iteration of LVShim 
Note: If the current is not accepted, the delta currents in the LVShim user interface change to purple and the new Loaded Current column is not displayed.