3.0T split-top head coil SNR test and troubleshooting

1. From the scan desktop, start a new scan by selecting Create New Worklist.
   1. Type geservice for Patient ID and 111 for Patient Weight in pounds.
   2. Click Show All Protocols to open the protocols window.
2. Remove all other surface coils from the cradle. Place the split-top head coil on the patient table with the P connectors extending into the magnet.
   1. Lock the baseplate into the table slots.
   2. Connect the P connectors on the MR unit (LPCA port P1).
      Note:

      The cables from the head coil to the LPCA should not have crossovers or loops evident from the outside.

3. Remove any pads from the coil, and unlock and remove the top half of the coil by depressing the latches on either side of the coil.
   1. Place the head phantom, loader shell, and phantom positioner pad into the head coil.
   2. Set the phantom into the coil, and reattach the top half of the coil.
4. At the magnet, press the Alignment Light button, and align the laser crosshair with the loader shell crossmark. Press Landmark to landmark the alignment.

   

   Item	Description
   1	Confirm that the wider portion of the coil is at the back, towards the MR system.
   2	Loader shell cross mark.

5. Move the coil to the scan position by pressing Move to Scan, while ensuring the cables do not get snagged.
6. At the console, set the protocols per the Signal section in Table 3. (On 3.0T systems, GE service personnel can use the Head SNR Signal protocol in the GE/Other protocol folder.)
7. Click Save Rx to download the protocols, then click Prepare to Scan.
8. Run Auto Prescan, and record the R1, R2, and TG values. (R1 should equal 11 and R2 should equal 14.)
9. If values are not correct, run Manual Prescan and adjust the R1 and R2 values. Click Done when complete.
10. Click Scan.

A signal scan must be run before the noise scan because the same R1, R2, and TG values must be used for both the signal and noise scans. Do not run an Auto Prescan before the noise scan because the values will be changed.

1. Copy the signal scan series. Right-click Signal Series and select Copy Series. Click Paste Series in the Rx Manager.

   On 3.0T systems, GE service personnel can use the Head SNR Noise protocol in the GE/Other protocol folder.

2. Click View Edit and set the protocols per the Noise section from Table 3.
3. Click Save Series and Prepare to Scan.
4. Open the Display CVs menu under Research Options. Set the rhformat and do_noise CVs to 1.
5. Run Manual Prescan, but do not make any changes. Click Done.
6. Click Scan.

   Table 3. Signal and Noise Protocols

   Protocol	Signal	Noise
   Patient Exam Information
   Patient ID	geservice	geservice
   Patient Name	HEAD	HEAD
   Patient Weight	111 lb (50 kg)	111 lb (50 kg)
   Patient Position
   Patient Position	Supine	Supine
   Patient Entry	Head First	Head First
   Coil	HEAD	HEAD
   Series Description	Signal	Noise
   Imaging Parameters
   Plane	Sagittal	Sagittal
   Mode	2D	2D
   Pulse Seq	FSE-XL	Gradient Echo
   Imaging Options	None	None
   PSD Name	Leave blank	Leave blank
   Scan Timing
   # of Echoes	1	1
   TE	17	Min Full
   TR	750	50
   Echo Train Length	4	N/A
   Bandwidth	31.25	31.25
   Additional Parameters
   Flip Angle	N/A	1
   Acquisition Timing
   Freq	512	512
   Phase	256	256
   NEX	1	1
   Phase FOV	1	1
   Freq DIR	A/P	A/P
   Shim	Auto	Auto
   Phase Correct	On	N/A
   Contrast	Off	Off
   Scanning Range
   FOV	24	24
   Slice Thickness	3	3
   Spacing	1.5	1.5
   Start R/L	0	0
   P/A Center	0	0
   I/S Center	0	0
   End R/L	0	0
   Slices	1	1
   Table Delta	0	0

Use a circular region of interest (ROI).

1. Select ROI as 80% of the phantom image for the signal scan. For the noise scan, choose 100% of the rectangular ROI.
2. ROIs in both signal and noise images can be measured directly in the image browser:
   1. Select MEASURE .
   2. Select the rectangular shape, and adjust its size and orientation so that the ROI is similar to the examples in Figure 2 and .Figure 3.
   Note:

   The ROI displays in the lower right corner of the image along with the Mean, Standard Deviation, and Area of ROI.

   

   

3. Record the values for mean signal, mean noise, and SNR in the data sheet below.

   Table 4. SNR Data Sheet

   Date	Mean Signal	Mean Noise	SNR

4. Individual receiver SNR is defined as the mean of data within the signal ROI divided by the mean of data within the noise ROI (with a correction factor).

   

   Note:

   The SNR calculation uses the MEAN of the signal image and MEAN of the noise image.

The SNR measurements must be greater than or equal to the SNR specification of 21.8 for the 3.0T split-top head coil.

No cable continuity check is recommended for the connector because of pin damage concerns.

1. Check the P connector for mechanical damage such as cracks.
2. Inspect the contact pins in the P connector for damage from improper insertion or corrosion.
3. Make sure the cradle latches and top latches are operating and have adequate range of motion.
4. Confirm that the coil P-connector T-handle spindle is properly lubricated and not worn. (Worn spindles contribute to a loose mechanical connection, intermittent MC bias faults, and in extreme situations, poor SNR.) Replace worn spindles per ODU Connectors Cleaning and Replacement.

If unable to prescan, or scanning but receiving no signal:

1. Check that the top half of the coil is latched properly to the bottom half of the coil.
2. Confirm that the landmark is correct and the cradle did not unlatch.
3. Verify that the scan locations and any FOV offsets are correct.
4. Try scanning again.
   Note:

   Be sure to remove the head coil from the magnet bore before scanning with the body coil.

   • If still unable to receive signal, try to scan (transmit and receive) with the body coil.

   • If scanning is happening, the problem is with the coil. Follow the guidelines in 3.

1. If the SNR fails for the coil with a normal signal and noise too high, or with signal too small, order the preamp and replace it.

   Refer to 3.0T Split-Top Head Coil FRUs and Replacement for replacement instructions for the TR board or preamp.

2. (For Rev 12 coil onwards) If the coil is not scanning with a TR Bias Fault failure, the problem is with the interface QHTR assembly. Replace the QHTR I/F Cable Assembly (P/N 5437386).
3. (For Rev 1 through Rev 11 Coil) If the coil is not scanning with a TR bias fault failure, the problem is with either the TR board or the preamp.

   • If one or all PIN diodes (D1, D2, D3, D4, D5) shows a short, order the TR board (P/N 5366299) for replacement.

   • If all PIN diodes are good (in both forward and reverse bias), order only the preamplifier (P/N 5433509).