SIGNA™ Hero 3.0T Service Methods
5852800-8EN Revision 1.0
Object ID: 00000018WIA30940F20GYZ
Topic ID: id_13106358 Version: 2.17
Date: Oct 7, 2021 3:41:53 PM

LVShim Procedures

Prerequisites

Table 1. Personnel requirements
Required persons	Preliminary requirements	Procedure	Finalization
1	None minutes	30 minutes	10 minutes

Table 2. Tools and test equipment
Item	Quantity	Effectivity	Part number	Manufacturer
LV shim phantom inner sphere	1	-	2274476	-
LV phantom small half ASM	1	-	2306642	-
LV phantom big half ASM	1	-	2306645	-

Table 3. Safety

Warning

Poison Hazard!

Green Phantoms contain nickel, a suspected carcinogen.

Do not ingest. Dispose of as hazardous waste according to state and federal regulations.

Warning

Poison Hazard!

Pink phantoms contain silicon oil.

Do not ingest. Dispose of as hazardous waste according to state and federal regulations.

Table 4. Required conditions
Condition	Reference	Effectivity
Confirm that passive shimming is complete and is within specification. Perform Grafidy Eddy Current Calibration.	-	-
Run Dual drive quadrature tool.	-	-
Remove all coils from the cradle and phantoms from the bore.	-	-

About this task

LVShim - Gradshim

The objective is to perform fine-tuning of the homogeneity of the magnet by using gradients only. The Gradshim is performed on 22 cm DSV. Test mode is performed in 5 volumes for peak to peak and rms values. The UI accordingly shows these values and their specs. Once the scan passes and all harmonics are within specification, the magnetic field is reanalyzed in Test mode.

The Gradshim process includes LVShim - Test. The objective of this test is to analyze completed scans at 45 cm DSV without calculating currents.

Topic ID: id_SL4463850-1178716

Preparing for LVShim Procedure

Procedure

Notice

Perform a Localizer scan to verify that the phantom is centered before performing the LVShim.
To set up the phantoms and system for this procedure, follow the instructions and procedures.
Set up LVShim procedure .
1. Set up and align the LVShim phantom
  
  Note: No phantom positioner is needed. Place LV Shim phantom directory on the cradle.
  
  Figure 1. Placing LVShim Phantom on Patient Table
2. Landmark on the LVShim phantom crosshairs.
Press the Advance to Scan button.
Perform a phantom centering check scan and center frequency check using manual prescan, and save the resulting frequency using Save Frequency.
Start the LVShim tool from the Common Service Desktop, on the Calibration tab.
- Non-proprietary: Select LVShim from the Calibration menu, and click the link labeled Click here to start this tool.
- Proprietary: Select the Calibration tab, click Installation and Calibration, and then select the shim to be performed (Gradient Shim).

Topic ID: id_SL4464188-1178716

Gradshim LVShim Procedure

About this task

By default, Gradshim is performed in Auto mode, though Manual mode is also available. Both modes are described below.

Topic ID: id_SL4464189-1178716

Auto Mode

About this task

In Auto mode, gradient currents are automatically calculated after you click Scan to fine tune the homogeneity of the magnet. In this mode, the tool stops after the X, Y and Z harmonics are within specification. In Test mode, the image from the last scan is automatically reanalyzed.

Procedure

Prepare the phantom for the LVShim procedure as described above.
Select Gradient Shim and click Scan.
Figure 3. LVShim tool user interface

In Auto mode, the tool does the following:
- Sets up the protocol and collects image data
- Calculates linear harmonics and compares it with the specification
- Calculates the delta currents and the new currents based on the harmonics
- Completes multiple iterations (maximum = 5) until harmonics meets the specification
- Shows the reanalysis of the last iteration in the final column in Test mode (customer acceptance specification)

Topic ID: id_SL4464199-1178716

Manual Mode

Procedure

Prepare the phantom for the LVShim procedure as described above.
Select Gradient Shim and Manual Mode, then click Scan (see Figure 3).
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 4. 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 5. Original Delta and New Currents (Examples)
To accept or decline the new currents:
1. If X/Y/Z harmonics data cells are green, decline the new currents by clicking the Cancel button. Ignore cells with the specification NA.
2. 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 . Repeat Figure 4.
If after five manual iterations any cell is still red, click More Actions and select Expert Mode. (For a description of Expert Mode functions, see Step Expert Mode Features of LVShim).
For more details about the scan (cal file name, center frequency, etc.), select More Actions > More Info.

Figure 6. More Information on Scan
When all iterations are complete and all harmonics are within specification, click Exit in the LVShim window .

If any harmonics fail in Gradshim, re-run Grafidy 3 Eddy Current Calibration.

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

Topic ID: id_14978685

Finalization

Procedure

For Gradshim, continue with the following steps.
Remove any phantoms and/or tools used.
Perform a Check Scan before turning the unit over to the customer.