Quality Assurance

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Quality Assurance

Calibration Procedures

Calibration procedures should be performed for quality assurance and in order to evaluate the performance of the MEG system.


CALIBRATION PROCEDURE: PERFORM WHENEVER:
1. Noise / Gain Measurement -there is line frequency noise
2. Head Coil Calibration -head localization results / accuracy is in doubt
3. EEG Gain Calibration -EEG results are uncertain
4. Magnetic Phantom Measurement -the performance of the MEG system is in question



MEG Noise Collection

Noise collection calibration procedures will be performed for quality assurance whenever necessary to evaluate the performance of the MEG system. Noise collection is performed to determine the noise level of each individual channel. Data is collected with no subject and all noise sources are removed from the immediate vicinity of the MEG system.


I. Procedure for acquiring data:

  • Make sure that the Magnetic Phantom is not connected / setup performing a noise collection.
1. Close the door to the MSR.
2. Click” Acq Manager” (or click on the Terminal Screen and type “Acq” at the prompt line; then go to step# 6.)
a. Click on “Select User”.
3. Select “meglab”.
4. Click on “Launch Acq”.
5. Select the study type: “Noise”.
a. Click on “Ok”.
6. At the Acq Window:
a. Click on “Acquire data”.
7. Create Directory? Select “Ok”.
(If this is the first recording of the day you will need to create a directory)
8. At the Acquisition Monitor Window adjust the scale.
9. Click on Start. There are 10 -10 sec trials.
10. When the collection is done click “Ok” at the “General Information Window”.


II. Procedure for Plotting the Data:

1. At the "General Information Window" click on "Tools".
2. Click on DataEditor.
3. Click on Set.
a. Select “MEG Left+ZF ZO” channel array.
4. Frequency Spectrum Display icon.
a. Display.
b. Trial.
c. Stack all trials.
5. Change y axis to “5f to 10f”. Hit Enter.
6. List channels that have increased power on the Daily Log.
7. File.
a. Print (Left channel array) to “lwmeglab”.
b. OK.
8. File.
a. Close.
9. Click on Set.
a. Select” MEG Right+ZC ZP” channel array.
10. Frequency Spectrum Display icon.
a. Display.
b. Trial.
c. Stack all trials.
11. List channels that have increased power on log.
12. File.
a. Print (Right channel array).
b. OK.
13. File.
a. Close.
14. At the DataEditor window:
a. Click on File.
b. Exit.
15. File
a. Close Window.
16. At the Acq window:
a. File.
b. Exit.


Head Coil Calibration

Head Coil Calibration will be performed for quality assurance as part of the maintenance and calibration procedures whenever: 1) necessary to evaluate the performance of the head coil, 2) a head coil is replaced or to evaluate the performance of the MEG system.


Two Point Calibration Head Coil Calibration using the Magnetic Phantom Each coil is placed in two positions on the lower calibration ring of the Magnetic Phantom. Two recordings are collected with the 3 or 4 head coils positioned on the calibration ring to determine the magnetic dipole moments of the head localization coils.

I. Head Coil Setup:
1. Fasten the Head Coils to the calibration points located on the outside surface of the Dewar using the white plastic screws. Plug the other ends into MEG jack box. Head coils are placed as usual with:
a. The red coil affixed to the right calibration point (if facing the dewar; your left),
b. The green coil attached to the left side,
c. The blue in the mid front and
d. The yellow (spare) mid back.


II. Calibration Program:
1. Open a Terminal window.
a. Type: su meg (lowercase).
b. Enter password: “omega2000”.
c. Enter: “calibrateCoils”.
III. Calibration Procedures:
1. Type “calibrateCoils” at a command line prompt
(or click on the calibrateCoils icon on the desktop).
2. Verify the head localization parameter file.
3. Hit ENTER if correct. (MO15_1609.hz.rp)
4. Hit ENTER to backup the current head localization parameter (rp) file and verify serial numbers.
5. Do you want to calibrate the ADC? Enter: “YES”.
6. DSQ Electronics Setup menu displays.
7. Calibrate the ADC units used to apply signals to the head localization coils.
a. Click on Channel Selector - right arrow. Start @ ADC 15. (calibrate each ADC individually; there are 16 ADC’s)
b. Click on Start Collection.
8. Click on File.
9. Exit.
10. Do you want to enter coil frequencies manually? Enter Y for yes.
11. To accept frequency values for coils hit ENTER.
IV. Starting Data Collection #1
1. Hit ENTER to launch Acq to start Data Collection #1.
2. Hit ENTER to select turn reference channels off.
3. Once Acq has started click on Acquire Data.
4. At the Question Menu click Yes.
5. Click OK for the folder name if asked.
6. Decrease scale.
7. When data starts scrolling across the screen, click on the Start button.
8. When the window appears indicating that trial #1 has been collected, click the OK button.
9. Select Close Window menu item from the File Menu.
10. Select Exit from the File Menu.
11. When Acq exits, hit the ENTER <Y> key to verify the data set collected.
V. Starting Data Collection #2
1. Swap the head coils for the second data collection:
a. Swap the left (green) with the right (red) head coil;
b. Swap the front (blue) with the back (yellow) head coil.
2. Hit ENTER to launch Acq for Data Collection #2.
a. Hit ENTER to select turn reference channels off.
b. Once Acq has started click on Acquire Data.
c. At the Question Menu click “Yes”.
d. Decrease scale.
e. When the window appears indicating that trial #2 has been collected, click the OK button.
f. Select Close Window menu item from the File Menu.
g. Select Exit from the File Menu.
h. When Acq exits, hit the ENTER <Y> key to verify the data set collected.
3. The distance between configurations #1 and #2 for each coil will be calculated and displayed. Hit ENTER to accept the distance.
Note: The distance should be 51.49 cm for the Omega-275 System.
4. The moments will be calculated for each coil and displayed. Hit ENTER to accept these values.
Note: a typical coil moment is 1.7e+11 to 1.8e+11 (fT*cm3)/A. Our range is: 1.6e+11 to 1.8e+11.
5. Hit RETURN to launch Acq (writes values into the parameter (rp) file).
6. At the Question “Do you want to use these values/”, click “Yes” or hit the Enter key to accept the results.
7. At the prompt “Remove calibration results datasets” hit RETURN to remove.



Important!!! Please perform a phantom dipole test to verify the new calibration moments!
*Disassemble the Magnetic Phantom before performing any noise collection.



EEG Gain Calibration

Magnetic Phantom Measurement

Variance Reporting / Process Improvement