LVShim Software

The LVShim software consists of three elements:

The LVShim PSD: Defines the pulse sequence data base (PSD) used to acquire the LVShim scan data.
LVShim Calibration File Generator: Generates LVShim calibration files.
LVShim Analysis Tool: Analyzes the scan data acquired by the LVShim PSD, and computes the magnetic field inhomogeneity and new shim current settings.

The subjects covered in this document:

Magnet Serial Number, Magnet Serial Number
Calibration File Type, Calibration File Type
Calibration File Name, Calibration File Name

Shim Type, Shim Type
Image Data. Image Data
Operation Mode, Operation Mode
Display Magnitude and Phase Difference Images, Display Mag and Phase Diff Images

1 Overview

LVShim calibration files contain coil characterization data used by the LVShim analysis tool to calculate the new currents needed to correct for magnetic field inhomogeneity. Generic shim calibration files are supplied with the system software for all gradient coils and for GE S/C shim coils.

2 Magnet Serial Number

The magnet serial number is used by LVShim to determine the appropriate set of calibration files to display during the shimming process. The magnet serial number must be correctly entered in the MR Configuration file. (The Magnet Type field is no longer used by system software tools.) Table 1 shows the value for each magnet type.

Table 1. Magnet Serial Values
Magnet Type	Value	Magnet Type	Value
S-III	Dxxxx	Cx 1.5T	Nxxxx
S-IV	Gxxxx	LCC 1.5T	Rxxxx
S-V	Jxxxx	LCC300 (3.0T)	Wxxxx
S-X	Xxxxx	3T/94	3xxxx
S-Xc_1	Kxxxx
S-Xc_2	Lxxxx

3 Calibration File Type

The software displays only the Calibration file types appropriate for the type of magnet being shimmed. Refer to Table 2.

Table 2. Calibration File Types for Each Type of Magnet
Magnet Type	Calibration File Type
Magnet Type	Gradient	Resistive	Res and Grad*	S/C 12 1.5T	S/C 18 1.5T	S/C 14 3.0T	S/C 18 3.0T
S-III	X		X		X
S-IV	X	X**			X
S-V	X			X
Cx, LCC 1.5T	X				X
Cx, LCC 1.0T	X
LCC300***	x					X	X
3T/94***	x						X
* The Res and Grad shim type always displays for S-I magnets, but displays for S-II/S-III magnets only when the Spectroscopy RF Amplifier variable is set to Yes in the MR Configuration file. The resistive shim option for GE S-IV magnets (Catalog No. M1040CH) consists of three coils: Z2, ZX, and ZY. The resistive shim power supply assembly contains six power supplies (Z2, Z3, ZX, ZY, X2-Y2, and XY), but only Z2, ZX, and ZY are used. However, the software does not support this three-coil matrix at this time. * For 3T/94 and LCC300 magnets: Even though the calibration file shows 18 coils, only 14 coils exist in the magnet.

4 Calibration File Name

Figure 1 is an example of a shim calibration file with the name components explained.

Figure 2 is an example of a gradient shim calibration file.

Refer to Table 3 for a list of the available coils.

Table 3. Coil Types
Coil	Description
3gc	Gradient (all magnets)
9rgc (Note 1)	Gradient/Resistive (S-I, S-II, and S-III)
6rc	Resistive (S-I, S-II, and S-III)
18sc	18-coil Supercon (S-II, S-III, S-IV, S-X, S-XC_1, Cx 1.5T, Cx 1.0T, LCC 1.5T, (3T/94, LCC300 (Note2))
Note 1: The resistive shim option for GE S-IV magnets (Catalog No. M1040CH) consists of three coils: Z2, ZX, and ZY. The resistive shim power supply assembly contains six power supplies (Z2, Z3, ZX, ZY, X2-Y2, and XY), but only Z2, ZX, and ZY are used. However, the software does not support this three-coil matrix at this time. Note 2: 3T/94 and LCC 300 calibration file lists 18 coils, even though only 14 coils exist in the magnet.

The S/C shim calibration files are divided into magnet/coil type, then by four file types: 22dsv.full, 32dsv.full, 40dsv.full, 45dsv.full, 40dsv.half, and 45dsv.half. The number signifies the diameter of the spherical volume.

The 22dsv.full files are used during Rough and Gradient LVShim.
The 32dsv.full files are for troubleshooting purposes only.
The 40dsv.full (for CRM Body Coil) and 45dsv.full files are used during Main LVShim.
The 40dsv.half and 45dsv.half files are half-current files used in cases where the full file is "overshooting" the target value.

Table 4 lists the generic calibration files supplied with the system.

Table 4. Generic Gradient and S/C Shim Calibration Files
File Type	Magnet Type	Shim Calibration File Names
3-Coil Gradient	All	lv_brm_acgd_3gc_22dsv
		lv_brm_acgd_3gc_45dsv
		lv_crm_acgd_3gc_22dsv
		lv_crm_acgd_3gc_40dsv
		lv_trm_acgd_3gc_22dsv.whole
		lv_trm_acgd_3gc_22dsv.zoom
		lv_trm_acgd_3gc_40dsv.zoom
		lv_trm_acgd_3gc_45dsv.whole
14-Coil Superconductive	LCC300	lv_30t_18sc_22dsv.corona
		lv_30t_18sc_22dsv.corona.half
		lv_30t_18sc_32dsv.corona
		lv_30t_18sc_32dsv.corona.half
		lv_30t_18sc_40dsv.corona
		lv_30t_18sc_40dsv.corona.half
		lv_30t_18sc_45dsv.corona
		lv_30t_18sc_45dsv.corona.half
18-Coil Superconductive	GE S-II, S-III, S-IV, Cx 1.5T, LCC 1.5T, LCC 1.5T (RB)	lv_15t_18sc_22dsv.full
		lv_15t_18sc_32dsv.full
		lv_15t_18sc_40dsv.full
		lv_15t_18sc_45dsv.full
		lv_15t_18sc_40dsv.half
		lv_15t_18sc_45dsv.half
		lv_15t_18sc_45dsv.rb
12-Coil Superconductive	GE S-V	lv_15t_12sc_22dsv.full
		lv_15t_12sc_32dsv.full
		lv_15t_12sc_40dsv.full
		lv_15t_12sc_45dsv.full
		lv_15t_12sc_40dsv.half
		lv_15t_12sc_45dsv.half
3-Coil Gradient	3T/94	lv_crm_acgd_3gc_40
3-Coil Gradient	3T/94	lv_crm_acgd_3gc_40

5 LVShim Analysis Tool Details

5.1 Shim Type

The software displays only the shim types associated with the magnet being shimmed. Table 5 shows the shim types for each magnet.

note:

When Test is selected as the Shim Type, new shim currents are not calculated during LVShim analysis.

Table 5. Types of Shims Available
Magnet Type	Shim Type Labels
S-III	Gradient	Res and Grad*	Sup18_1.5T	Test
S-IV**	Gradient	Sup18_1.5T		Test
S-V	Gradient	Sup12_1.5T	Passive	Test
Cx, LCC 1.5	Gradient	Sup18_1.5T		Test
LCC300	Gradient	Sup18_3.0T		Test
3T/94	Gradient	Sup18_3.0T		Test
* The Res and Grad shim type always displays for S-I magnets, but displays for S-II/S-III magnets only when the Spectroscopy RF Amplifier variable is set to Yes in the MR Configuration file. ** The resistive shim option for GE S-IV magnets (Catalog No. M1040CH) consists of three coils: Z2, ZX, and ZY. The resistive shim power supply assembly contains six power supplies (Z2, Z3, ZX, ZY, X2-Y2, and XY), but only Z2, ZX, and ZY are used. However, the software does not support this three-coil matrix at this time.

5.2 Image Data

Image Data refers to the exam, series, and image number of the image data set to be processed. If an LVShim scan was just performed, the program automatically picks up the last exam, last series, and first image number of the last set of images scanned and makes it the default choice. If the last scan was not an LVShim scan, Image Data is shown as none selected.

Select this menu item when the image data displayed by the software are incorrect. When Image Data is selected, the software prompts for the correct exam, series, and image numbers. If the exam, series, or image number of the image data to be processed is not known, enter 0 (zero) when prompted for a number; this provides a list of the existing exams, series, or images.

For the TwinSpeed, take care to select the series corresponding to the same GradMode highlighted upon entering the LVShim Analysis Tool.

5.3 Operation Mode

There are two operation mode options: Service and Research, and Table 6 describes them.

Table 6. Service and Research Operation Modes
Option	Description
Service	This mode should be used for Rough and Main LvShim and Gradient shimming for all magnet types. This mode also includes all the LVShim features needed to build a shim calibration file.
Research	This mode should be used for Rough and Main LVShim troubleshooting only. While in the Research mode, the user can configure out selected coils during shimming.

5.4 Display Magnitude and Phase Difference Images

This option allows the display of each magnitude image and masked phase difference image in a separate window (shown in Figure 3) after the image data is processed. Both windows are updated when an alternate scan plane is selected. These windows will initially display in the upper right corner of the screen; reposition as necessary for viewing the LVShim Analysis window.

5.5 Calibration File Name Token

The calibration file name token is used to help distinguish similar calibration file names from each other. The token is attached at the end of the calibration file name. Refer to Calibration File Name, Calibration File Name, for more information.