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-603102, India 2National Institute of Mental Health and Neurosciences, Bengaluru-560029, India 3Central Institute of Plastic Engineering & Technology, Chennai-600032,India giri@igcar.gov.in ICEC 26 03/10/2016

Plan of the talk Introduction to MAGNETOENCEPHALOGRAPHY Details of MEG cryostat Insert details Testing of the system Results & Discussions ICEC 26 03/10/2016

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 ICEC 26 03/10/2016

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 ICEC 26 03/10/2016

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 ICEC 26 03/10/2016

Biomagnetic signals are low level, low frequency signals MCG B (Tesla) Biomagnetic signals are low level, low frequency signals MCG MEG ICEC 26 03/10/2016

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) -- 0.01 Hz : > 38 dB (80) -- 0.1 Hz : > 40 dB (100) -- 1.0 Hz : > 60 dB (1000) -- 10 Hz : > 80 dB (10,000) -- 100 Hz : > 100 dB (100,000) -- 1000 Hz : > 100 dB (100,000) -- 1000 Hz to 180 MHz : > 100 dB (100,000) ICEC 26 03/10/2016

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 ICEC 26

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) -- 0.01 Hz : > 38 dB (80) -- 0.1 Hz : > 40 dB (100) -- 1.0 Hz : > 60 dB (1000) -- 10 Hz : > 80 dB (10,000) -- 100 Hz : > 100 dB (100,000) -- 1000 Hz : > 100 dB (100,000) -- 1000 Hz to 180 MHz : > 100 dB (100,000) 03/10/2016 ICEC 26

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 ICEC 26 03/10/2016

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 ICEC 26 03/10/2016

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 ICEC 26 03/10/2016

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: 255.2 mm ICEC 26 03/10/2016

Drawing of the Sensor holder, Fabricated Sensor holder & LN2 Testing of the holder ICEC 26 03/10/2016

Magnetic field noise spectra of a typical gradiometer and a magnetometer Magnetic field noise as a function of channel number measured at 10 Hz ICEC 26 03/10/2016

MEG Time series Data Eyes closed Eyes opened ICEC 26 03/10/2016

MEG noise MEG Signal Eyes closed MEG Signal Eyes opened 03/10/2016 ICEC 26 03/10/2016

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. ICEC 26 03/10/2016

ACKNOWLEDGEMENTS Department of Atomic Energy Department of Science and Technology All our collaborators Special Thanks to All of you for your kind attention. ICEC 26 03/10/2016

Thank You ICEC 26 03/10/2016