1. Design and Development of helmet shaped SQUID sensor array holder for MEG studies
K.Gireesan1, T.S.Radhakrishnan1, Joseph Bensigh3, S.Sengottuvel1, Rajesh Patel1, N.Mariyappa2 S.K.Naik3, and M.P.Janawadkar1
1Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam , India
2National Institute of Mental Health and Neurosciences, Bengaluru , India
3Central Institute of Plastic Engineering & Technology, Chennai ,India
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2. Plan of the talk Introduction to MAGNETOENCEPHALOGRAPHY
Details of MEG cryostat
Insert details
Testing of the system
Results & Discussions
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3. MCG and MEG
Electrophysiology of heart / brain produces a distribution of electric potential and an accompanying magnetic field
ECG/EEG measures the distribution of electric potential
MCG/MEG measures the associated magnetic field
Magnetic field is extremely small (less than 2 pT)
Measurement requires SQUID sensors cooled to 4.2K
ADVANTAGES:
Non-contact and Non-invasive
Less affected by conductivity distribution of tissues
Permits better source localization accuracies
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4. Relative advantages and disadvantages of EEG & MEG
Signal magnitude
Large signal (10 mV), easy to detect
Tiny signal (100 fT), difficult to detect
Cost
Cheap
Expensive
What does signal measure?
Secondary (volume) currents
Fields generated by primary currents
Signal purity
Affected by skull, scalp, etc.
Unaffected by skull, scalp, etc.
Temporal Resolution
~ 1 ms
Spatial Localization
~ 1 cm
~ 1 mm
Experimental Flexibility
Allows some movement
Requires complete stillness
Dipole Orientation
Sensitive to tangential and radial dipoles
Sensitive only to tangential dipoles
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5. MAGNETOENCEPHALOGRAPHY (MEG)
SQUID sensors arranged over the whole head for MEG
Superconducting Quantum Interference Device (SQUID) is an extremely sensitive detector of magnetic field (~fT). It consists of a closed loop of a superconductor interrupted by two Josephson Junctions.
SQUID Sensors have applications in areas including Biomagnetism
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6. Biomagnetic signals are low level, low frequency signals MCG
B (Tesla)
Biomagnetic signals are low level, low frequency signals
MCG
MEG
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7. Shielding Performance of MSR:
Magnetic Shielded Room at IGCAR
Clear usable space : 4m (L) x 3 m (W) x 2.4 m (H)
2 layer µ metal 2mm & 3mm thick
2 layer Aluminium 4 mm & 8mm thick
Shielding Performance of MSR:
Shielding factor
-- DC > 57 dB (700)
Hz : > 38 dB (80)
Hz : > 40 dB (100)
Hz : > 60 dB (1000)
Hz : > 80 dB (10,000)
Hz : > 100 dB (100,000)
Hz : > 100 dB (100,000)
Hz to 180 MHz : > 100 dB (100,000)
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8. data as measured and unprocessed MCG Mesurement in progress
R-Wave Amplitude: ~ 80 pT (pp)
Field Noise 33 fT (rms)/√Hz
data as measured and unprocessed
MCG Mesurement in progress
Online display of the data on comp. screen
03/10/2016
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9. Shielding Performance of MSR:
Magnetic Shielded Room at IGCAR
Clear usable space : 4m (L) x 3 m (W) x 2.4 m (H)
2 layer µ metal 2mm & 3mm thick
2 layer Aluminium 4 mm & 8mm thick
Shielding Performance of MSR:
Shielding factor
-- DC > 57 dB (700)
Hz : > 38 dB (80)
Hz : > 40 dB (100)
Hz : > 60 dB (1000)
Hz : > 80 dB (10,000)
Hz : > 100 dB (100,000)
Hz : > 100 dB (100,000)
Hz to 180 MHz : > 100 dB (100,000)
03/10/2016
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10. Whole Head – 90 Channel MEG System
Sensor Array Helmet for MEG, developed by IGCAR-CIPET.
-- First Prize under Plastics for Health care– 2nd National Award Instituted by the Dept of Chemicals and Petrochemicals
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11. Sensor holder requeirment Space restriction 28 mm on sides
51 Planer Magnetometer on sides (10 mm x 5mm) and 35 gradiometer (20mm x 90 mm) on top
Material should be non magnetic and non metallic
Generally G 10 is being used
Molding is costly for one or two
Modification will be costly
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12. Additive manufacturing is suggested
Only selective materials can be used
No history of low temp. properties
Polycarbonate can be used for AM
Tested at LN2 temp. Found good
2 mm t will have enough strength
Threaded structure for holding sensors
No mould required.
Modification is possible without affecting cost
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13. Inner bottom of the cryostat
Dimensions of the HELMET SENSOR ARRAY: No. of channels: 90 - Inter-channel distance: 37 mm; Vertical distance between the Apex to the base: 181 mm; Distance between the bottom edge to the last row: 27 mm to 44 mm; The horizontal distance at Section AA: mm
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14. Drawing of the Sensor holder,
Fabricated Sensor holder & LN2 Testing of the holder
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15. Magnetic field noise spectra of a typical
gradiometer and a magnetometer
Magnetic field noise as a function of
channel number measured at 10 Hz
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16. MEG Time series Data
Eyes closed
Eyes opened
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17. MEG noise MEG Signal Eyes closed MEG Signal Eyes opened 03/10/2016
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18. We have also completed 86 channel MEG system
Conclusion
Conclusions:-
Polycarbonate material which is suitable for 3D printing is low temperature compactable.
With 2mm thickness it is having enough stiffness to rigidly hold the SQUID sensors.
We have also completed 86 channel MEG system
Average noise level are 5.5 fTrms/cm/√Hz & 38 fTrms/√Hz for gradiometers and magnetometers respectively.
Clinical studies will be carried out soon.
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19. ACKNOWLEDGEMENTS Department of Atomic Energy
Department of Science and Technology
All our collaborators
Special Thanks to
All of you for your kind attention.
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20. Thank You
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