Discovery MR750 3.0T System Service Methods
5690009-2EN Revision 4
Object ID: 00000018WIA302AAE20GYZ
Topic ID: id_13105928 Version: 3.16
Date: Nov 29, 2021 11:01:35 AM

RF body coil replacement

Prerequisites

Table 1. Personnel requirements
Required persons	Preliminary requirements	Procedure	Finalization
2 minimum	Not Applicable	240 minutes	40 minutes

Table 2. Tools and test equipment
Item	Quantity	Effectivity	Part number	Manufacturer
Small Carpenter’s Level	1	-	-	-
Field RF Coil Tuning Kit	1	-	5311727	-
Nonmagnetic Titanium Service Tool Kit, Large Set	1	-	5112581	-
Arc Detection Stress Test Kit	1	-	5401455-2	-
Elliptical Phantom and Test Fixture (for 750 Dual Drive Only)	1	-	5313739	-

Table 3. Consumables
Item	Quantity	Effectivity	Part number	Manufacturer
Adhesive	1	-	46-220312P1	-
Anti-Seize	1	-	2119594	-

Table 4. Replacement parts
Item	Quantity	Effectivity	Part number	Manufacturer
Discovery MR750 3.0T Body Coil and FRU Case	1	-	See FRU Manual.	-
FRU Kit for End Bell Foam Replacement 450, 750, 450w, 450w GEM (for 750 Dual Drive Only)	1	-	5498152	-

Table 5. Safety

Warning

Strong magnetic field

Ferrous materials can become dangerous projectiles in the presence of the magnetic field that the magnet produces.

Do not bring any ferrous tools or equipment into the magnet room.

CAUTION

Dangerous work area

Use of heavy equipment for coil removal and replacement is a hazard to all personnel in the area.

Set up restricted barriers and signs limiting access to the work area.
Notify all effected personnel in the area prior to starting the service activity.
Review safety procedures and restricted areas for the job.
Wear Personal Protective Equipment (PPE) at all times.
Refer to the Material Handling SRA before starting coil replacement.

Table 6. Required conditions
Condition	Reference	Effectivity
Contact a trained, local body coil tuning expert before starting this procedure, because the coil will need to be tuned as part of the replacement finalization. If necessary, contact the Modality Operations Manager for a list of trained individuals.	-	-

About this task

Use this procedure to replace the RF body coil.

Topic ID: id_SL12386133-1061851

Remove RF body coil

Procedure

Perform LOTO on the PDU/gradient subsystems, XRFD amplifier, and PEN cabinet. See MR Service Safety Manual, PN 5452735.
Note: Before removing the body coil or front end bell, perform End Bell Gap Check. See End Bell to Body Coil Gap Check.
Remove the split bridge. See Bridge and Longitudinal Drive Belt Replacement.
Remove the front end bell. See Front End Bell Removal and Installation.
Disconnect the two DD bias lines in the front, and the I and Q lines in the rear of the RF body coil.
Disconnect the bore lights from the RF body coil. Pop out the four pop pins before removing the bore lights.

Figure 1. Bore lights
(For MR750 systems with single drive RF amplifier) Visually inspect the gradient coil and body coil and determine whether additional shims have been installed between the two coils to help with body coil centering. If shims have been installed, note their quantity and exact location. As you remove the body coil, ensure that these shims are not lost. They will need to be reinstalled with the new body coil to ensure proper centering.
(For MR750 systems with dual drive RF amplifier) The replacement coil has centering feet already installed. No further action is needed for shimming.
Notice: Do not use the air hose manifolds to remove the RF body coil.
Partially slide out the old RF body coil, and disconnect the bore temperature sensor and tape it to the magnet enclosure so it is out of the way.

Figure 2. Bore temperature sensor cable
Notice: Do not use the air hose manifolds to remove the RF body coil.
Fully remove the coil and set it aside on the patient end.

Figure 3. Removing RF body coil

Figure 4. RF Body Coil on Patient End
If the system has a single drive RF amplifier, proceed to Install RF Body Coil for Single Drive.
If the system has a dual drive RF amplifier, proceed to Body Coil Alignment.

Topic ID: id_SL12386129-1061851

Install RF Body Coil for Single Drive

Procedure

Slide the new body coil into the magnet bore. The DD bias lines are in the front and the I and Q connectors face the rear.

Figure 5. Sliding in RF Body Coil
Before sliding the RF body coil in all the way, reconnect the bore temperature sensor to the coil (see Room Ambient and Bore Temperature Sensor Replacement).

If the system included shims between the gradient coil and the body coil centering pad Step 6, restore the shims to their original positions.

Note:
Failure to restore the shims to their original positions will affect body coil centering.
Align the I and Q connectors in the rear so they are as close to the 7 o’clock and 5 o’clock positions as visually possible.

Figure 6. Centering RF Body Coil
Press the RF body coil so the gap between the rear end bell and the RF body coil is 2.5 +/- 0.5 mm with a desired gap of 2.0 mm.
If removed, connect the four pop pins and install the bore lights to the body coil.
Reconnect the DD bias lines and I and Q lines.

Figure 7. Reconnecting DD bias lines

Figure 8. I and Q connectors
Re-install the front end bell. See Front End Bell Removal and Installation.

Confirm the gap between the front end bell and the RF body coil is 2.5 +/- 0.5 mm with a desired gap of 2.0 mm.
Proceed to Finalization.

Topic ID: id_SL12386136-1061851

Body Coil Alignment

Topic ID: id_SL12390737-1061851

End Bell to Body Coil Gap Check

Procedure

Perform LOTO on the RF amplifier and the PEN cabinet. See MR Service Safety Manual, PN 5452735.
Insert the replacement coil in the bore and re-install the front end bell securely before performing the gap check.

Note: The replacement body coil has the default shim feet installed. It is recommended that the default shims be used as the starting point for coil centering.
Check the RF body coil levelness (with respect to the x-axis) using the tubular level (5450084), which is included in the leveling kit. The bubble on the level should be between the two black lines when placed on the small RF cable cover between the two drive cable bulkheads in the rear of the body coil.
Check the gap between the front end bell and RF body coil, as well as the rear end bell and RF body coil using the gap tool (5391159).
Check the gap at several locations across the circumference to ensure it is uniform all around. The gaps should be between 2 and 2.5 mm (desired gap is 2 mm). If the gaps are not between 2 mm and 2.5 mm around the circumference, see the procedure in End Bell to Body Coil Gap Check to make this adjustment.
Note:
Rationale for gap distance:
- If the gap is too small, the end bell may come in contact with the body coil and cause the tuning, projection, uniformity, and other parameters to go out of specification or change if the end bell or coil is removed during a service event.
- If the gap is too large, there is potential for the body coil to move after the end bells are on, which could cause a parameter to go out of specification. If, for example, a patient were to push on the wall of the body coil enough to shift the coil, the end bells are designed to automatically re-center the coil (if the gaps are between 2 mm and 2.5 mm).
The gap tool (5391159) has three sections to help measure the gap.
Figure 9. Gap check using gap tool
- The NO GO section is 3.0 mm. If the NO GO section can fit in the gap, then the gap is too wide.
  
  Figure 10. Example: improper gap between front/rear end bell and RF body coil (too large)
- The GO portion is 2.0 mm. If the GO section cannot fit in the gap, then the gap is too narrow.
  
  Figure 11. Example: improper gap between front/rear end bell and RF body coil (too small)
- The SET section is 2.5 mm. This is the widest the gap can be. Ideally the gap should be 2.0 mm; therefore, the gap should actually be positioned with the GO section of the tool when adjusting end bells.
  Figure 12. Example: proper gap between front/rear end bell and RF body coil
  
  The proper gap is important and required to help keep the parameters of the system (such as uniformity, projection, body coil tuning) in specification. Measure the gap on the front AND rear end bell, and also in multiple locations around the circumference, including under the bridge.
Confirm the gaps between the front and rear end bells are between 2 mm and 2.5 mm around the entire circumference.

If the gaps on the front and rear end bells are correct, proceed to Manual pre-scan projection — image test.

If the gaps are not between 2 mm and 2.5 mm, proceed to Front end bell gap adjustment.

Topic ID: id_SL12390740-1061851

Front end bell gap adjustment

Procedure

Note: There is no way to directly adjust the front end bell. However, if adjustments are needed, align the body coil with the front end bell by moving the body coil. When the gap between the front end bell and the body coil is 2.0 mm to 1.5 mm, make the proper adjustments to the rear end bell.
Move the front end bell in place on the system. Start all M10 x 25 screws and nylon washers in place. Starting at the top (12 o’clock position), begin tightening screws.

Figure 13. Tightening screws on front end bell
Work around the end bell, tightening all screws about 2 turns per rotation. Move the RF coil forward or backward so that the minimum gap achieved (anywhere around the circumference of the RF coil and end bell interface) is 2 mm.

Figure 14. Gap check using gap tool
Verify the gap between the front end bell and the RF coil is no less than 2 mm and no greater than 2.5 mm, with a desired value of 2 mm.

Topic ID: id_SL12391500-1061851

Rear end bell adjustment

Procedure

Note:
This procedure can be done without the complete removal of the rear end bell. However, the rear end bell may need to be loosened. If preferred, it can be removed. The steps below detail only the adjustment portion. To remove the rear end bell, see Rear End Bell Removal and Installation.

Uninstall the bore lights by peeling off the lights on the inside of the RF coil. Keep the nylon push rivets for reinstallation.
Monitor and adjust the speaker cable wire at the top of the rear end bell so that it is not clamped or damaged. If necessary, remove the cooling air hoses and/or pull the rear pedestal back for extra room.
Move the rear end bell (out or in) to get a gap of 2 mm to 2.5 mm (desired gap is 2 mm) between the RF coil and rear end bell. Also account for the 2 mm to 2.5 mm gap required for the front end bell.

The rear end bell has adjustable studs (circled in image below) to which the end bell mounts. Adjust the studs by loosening the nuts on the shorter standoffs on the rear turtle ring arms (where the rear end bell will be mounted).

Figure 15. Adjusting gap between read end bell and RF body coil
Adjust the shorter standoffs using a flat blade screwdriver through the holes on the rear end bell. Back out each standoff, until standoffs lightly touch the backside flange of the rear end bell while maintaining a gap of no less than 2 mm and no greater than 2.5 mm (desired value of 2 mm between the RF coil and end bell.
The standoffs have a screwdriver slot at the bottom of the internal M10 threads. Using a flat blade screwdriver inserted into the standoff, adjust the smaller standoff by turning them in the turtle ring so the standoff is flush with the nut or contacts the magnet flange.
Tighten the screws while adjusting in the X and Y direction to achieve a uniform concentricity (2 mm to 2.5 mm uniform gap between end bell and RF). After tightening the M10 bolts to secure the end bell, check that the gap of no less than 2 mm and no greater than 2.5 mm is maintained between the RF coil and end bell. Top and sides are the priority. Using a wrench, tighten the nuts on the shorter standoffs behind the end bell to secure. After the standoffs are all adjusted, re-adjust the longer standoffs that attach the rear arcs and rear covers to the set height.

Topic ID: id_SL12391911-1061851

Manual pre-scan projection — image test

Procedure

Note: To perform this procedure, the service key must be installed.
Note: The Manual Prescan Projection test must be done with the end bells securely attached to the magnet in order to obtain the proper results.
Place the split bridge temporarily (without attaching the drive belt or mounting hardware) into the magnet. Engage the four M10 threaded bolts with the rear pedestal and set the L-brackets that are still attached to the upper bridge support bracket onto the lower bridge support bracket.

Figure 16. Upper bridge support bracket on lower bridge support bracket
Table movement must be emulated out in order to scan without a functioning LPCA. Emulate the table by doing the following:
1. Note: The Shell window can only be launched when the EA3 user is included in the authorized EA3 group. Users not in this EA3 group will not have access to launch the Shell window. If you are not logged on as the proper logon user, log out and then log back on as the correct EA3 user with the authorized permissions.
  Open a C Shell.
2. Type cd/w/config.
3. Type gedit mgd_stage
4. Type T (using upper case) in order to emulate the table
5. Save the mdg_stage file.
6. Perform a TPS reset.
Dock the table. Place the elliptical phantom and the phantom holder at the center (S/I) of the cradle. Set the angle of the phantom to 0 degrees. Manually move the phantom into the bore so that it is centered mechanically in the Z direction.
At the console, start the Uniformity Tool using the following steps.
1. Note: The Shell window can only be launched when the EA3 user is included in the authorized EA3 group. Users not in this EA3 group will not have access to launch the Shell window. If you are not logged on as the proper logon user, log out and then log back on as the correct EA3 user with the authorized permissions.
  Open a C Shell.
2. Type cd /usr/g/service/mclass/uniformity
3. Type touch .uniformity_enable
4. Type run_uniformity_tool
On the Uniformity Tool GUI, select single scan for Data Acquisition mode and select Quadrature Mode under Dual Drive mode. Then select Scan and Analysis to start the scan.
When the single scan completes, two pop-ups appear. One is titled “Profile of ePhantom”; the other is titled “Uniformity Plot of ePhantom.”

Figure 17. Profile of ePhantom

Figure 18. Uniformity plot of ePhantom
Record the Projection Value (PV).

Is Projection Value (PV) Percentage (%) greater than or equal to 96%?

Yes ___________

No ____________

If the projection value (PV) percentage is greater than or equal to 96%, the projection is considered acceptable. Proceed to Finalization.

If the percentage is less than 96%, the new centering pads are required. Proceed to RF body coil alignment — centering pads.

Topic ID: id_SL12391940-1061851

RF body coil alignment — centering pads

About this task

Because the projection was tilted and the PV percentage was under 96%. thicker centering pads are needed to properly center and secure the RF body coil. Applying difference sized centering pads optimize the uniformity by placing the coil in a better “electrical” center on each particular system. As the centering pad number gets higher, the thickness increases.

Table 7.
Centering Pad PN	Mark on Centering Pad	Thickness with Double Sided Tape Applied (mm)
5498416 (default)	None	5.46
5498416-2	2	5.71
5498416-3	3	5.97
5498416-4	4	6.22
5498416-5	5	6.48
5498416-6	6	6.73
5498416-7	7	6.98
5498416-8	8	7.24
5498416-9	9	7.49

Procedure

Remove the split bridge.
Disconnect the DD bias lines.
Remove the front end bell. See Front End Bell Removal and Installation.
Place a small piece of tape on the gradient coil acoustic liner so that the body coil position is clearly marked. This tape is used to align the body coil for the remainder of the procedure each time the body coil is re-installed.

Note:
The body coil levelness (with respect to the x-axis) is very important for the projection angle. From this point on, align the body coil using the side of the coil (right or left) that does NOT need a thicker centering pad. The tubular level (5450084) is no longer used because it was required for the baseline body coil alignment in Body Coil Alignment.

Figure 19. Temporary body coil alignment — tape on left side

Note: If the scan projection obtained looks similar to the illustration below, add a small piece of tape to the FRONT RIGHT (when looking at the magnet from the front) centering pad corner. Based on the direction that the projection angle is shown (which correlates with a positive sign on the angle), the thicker centering pads need to be installed on the LEFT side of the coil when looking at the magnet from the front.

Figure 20. Temporary body coil alignment tape on right side

Fully remove the RF body coil and set it on the patient end. Install new centering pads (using the double sided tape and screw) using the following table as a guideline for determining which of the thicker centering pads should be used.

If the Uniformity result has positive sign, the thicker centering pads should be installed on the LEFT side of the coil when looking at the magnet from the front.
If the Uniformity result has a negative sign, the thicker centering pads should be installed on the RIGHT side of the coil when looking at the magnet from the front.

Table 8. Number of centering pads by projection angle
Projection Angle (degrees)	Centering Pad (FRONT)	Centering Pad (REAR)
0–3	baseline	baseline
3–6	2	baseline
6–9	2	2
9–12	3	2
12–15	3	3
15–18	4	3
18–21	4	4
21–24	5	4
24–27	5	5
27–30	6	5
30–33	6	5
33–36	7	6
36–39	7	7
39–42	8	7
42–45	8	8
45–48	9	8
48–51	9	9

Note: Either the left or right side of the coil should retain the standard, or baseline, centering pads (5498416). Add thicker centering pads to only one side of the body coil.

The example Projection Angle result is 15.2 degrees, so the suggested centering pads to use are a ‘4’ in the FRONT and a ‘3’ in the REAR as shown in the table below. Based on the direction that the projection angle is tilted and because it has a positive sign, both the centering pads should be added to the LEFT side of the coil when looking at the magnet from the front.

Figure 22. Centering pads used for projection angle 15.2°

Re-install the body coil and position using the alignment tape.
Reconnect the DD bias lines.
Place the split bridge temporarily (without attaching the drive belt or mounting hardware) into the magnet.

Engage the four M10 threaded bolts with the rear pedestal and set the L-brackets that are still attached to the upper bridge support bracket onto the lower bridge support bracket.
Run the Uniformity Test again to confirm whether or not the new scan PV percentage is less than 96%

Note: The specification for body coil centering is PV percent must be greater than 96%. However it is recommended that you try to obtain a value close to 100%, as this will improve L/R shading.

If the PV percentage is greater than 96%, proceed to Step 18.

If the centering pads need further adjustment, proceed to Step 10.
Remove the split bridge.
Disconnect the DD bias lines.
Fully remove the RF body coil and set it on the patient end.

Install new centering pads based on the following guidelines:

If the FRONT centering pad is equal to or thicker than the REAR centering pad, use Table 9.

Table 9. Extra pad quantities by projection angle (equal to or thicker scenario)
Projection Angle (degrees)	Centering Pad (FRONT)	Centering Pad (REAR)
3–6	No Change	Previous Pad + 1
6–9	Previous Pad + 1	Previous Pad + 1
9–12	Previous Pad + 1	Previous Pad + 2
12–15	Previous Pad + 2	Previous Pad + 2
15–18	Previous Pad + 2	Previous Pad + 3
18–21	Previous Pad + 3	Previous Pad + 3
21–24	Previous Pad + 3	Previous Pad + 4
24–27	Previous Pad + 4	Previous Pad + 4

Note: The final centering pads used should be within 1 thickness step of one another to optimize the balance between the front and rear. For example, if a ‘4’ centering pad was used in the FRONT, then the REAR must use a ‘3’, ‘4’, or ‘5’ centering pad.

Equal to or Thicker Scenario:

If the previous centering pads installed were a ‘4’ in the FRONT and a ‘3’ in the REAR, and the Uniformity resulted in an angle between 9 and 12 degrees, then the centering pads should be changed to a ‘5’ in the FRONT and a ‘5’ in the REAR.

If the FRONT centering pad is thinner than the REAR centering pad, use Table 10.

Table 10. Extra pad quantities by projection angle (thinner scenario)
Projection Angle (degrees)	Centering Pad (FRONT)	Centering Pad (REAR)
3–6	Previous Pad + 1	No Change
6–9	Previous Pad + 1	Previous Pad + 1
9–12	Previous Pad + 2	Previous Pad + 1
12–15	Previous Pad + 2	Previous Pad + 2
15–18	Previous Pad + 3	Previous Pad + 2
18–21	Previous Pad + 3	Previous Pad + 3
21–24	Previous Pad + 4	Previous Pad + 3
24–27	Previous Pad + 4	Previous Pad + 4

Note:

The final centering pads used should be within 1 thickness step of one another to optimize the balance between the front and rear. For example, if a ‘4’ centering pad was used in the FRONT, then the REAR must use a ‘3’, ‘4’, or ‘5’ centering pad.

Thinner Scenario

If the previous centering pads installed were a ‘2’ in the FRONT and a ‘3’ in the REAR, and the Uniformity resulted in an angle between 9 and 12 degrees, then the centering pads should be changed to a ‘4’ in the FRONT and a ‘4’ in the REAR.

Note:

If the new centering pads were too thick and your projection angle is now outside of the target +/- 3 degree range in the opposite direction (meaning the sign of the angle has flipped from positive to negative or negative to positive and the tilt of the projection scan is going in the opposite direction), reduce the thickness of the centering pads assuming a single pad step is equivalent to 3 degrees.

For example, suppose the previous Uniformity result was +10. Per the table above, a ‘3’ centering pad would have been used in the FRONT, and a ‘2’ centering pad would have been used in the REAR. If the new Uniformity result is ‘-5’, then the centering pads used were too thick. Reducing one of the pads should make the Uniformity result go from ‘-5’ to ‘-2’ and reach the desired +/- 3 degree range. Because the goal is to optimize the balance between the front and rear, the ’3’ centering pad used in the FRONT should be changed to a ’2’.

Reinstall the body coil and position using the alignment tape.
Reconnect the DD bias lines.
Place the split bridge temporarily (without attaching the drive belt or mounting hardware) into the magnet.
Engage the four M10 threaded bolts with the rear pedestal and set the L-brackets that are still attached to the upper bridge support bracket onto the lower bridge support bracket.
Run the Uniformity Test again to confirm whether or not the new scan projection angle and PV percentage is acceptable.
- It the PV percentage is greater than 96%, proceed to Step 18.
- If the centering pads need further adjustment, return to Step 10.
Record the final PV percentage.

Record Final Exam #: ___________________

Record Final Uniformity Angle: ____________

Record Final PV%: _____________________

Record location of centering pads (circle one) Right or Left (when looking at magnet from the front)

Front Baseline 1 2 3 4 5 6 7 8 9
Rear Baseline 1 2 3 4 5 6 7 8 9
Proceed to Finalization.

Front	Baseline	1	2	3	4	5	6	7	8	9
Rear	Baseline	1	2	3	4	5	6	7	8	9

Topic ID: id_14997180

Finalization

Procedure

Note: RF coil tuning can be done only by personnel who have successfully completed GE Healthcare’s training class for Body Coil Tuning and Stress Test, GEHC-TECH-AMSC-MR5037.
Have the previously contacted, properly trained body coil tuning expert tune the RF body coil.
Run TR Dynamic Disable Calibration.
Run Troubleshooting the Daily Quality Assurance (DQA) II tool.
Run LVShim — Gradshim.
Run System gain calibration.
Run Echo Planar Test (EPT).
Do SaveInfo.
Do a quick head and body scan to ensure the system is functioning properly.