FEASIBILITY STUDY AND PROTOTYPING OF AN ELECTROMAGNETIC …
Transcript of FEASIBILITY STUDY AND PROTOTYPING OF AN ELECTROMAGNETIC …
FEASIBILITY STUDY AND PROTOTYPING OF AN ELECTROMAGNETIC CORTICAL STIMULATOR FOR BRAIN
MAPPING IN OPEN SKULL NEUROSURGERY
Thesis of: Anna Mafrica
Supervisor: Giancarlo Ferrigno
Co-supervisors: Elena De Momi, Riccardo Bertacco, Christian Rinaldi
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INTRODUCTION
BRAIN TISSUE REMOVAL
BRAIN MAPPING
To localize principal functional areas of the brain,such as:- Motor cortex- Areas related to memory- Areas related to speech- …
Preserving brain functionalities during resection of thepathological area:
- Brain tumors ⟶ new cases each year: 21 peopleover 100.000 (http://www.cbtrus.org)
- Epilepsy ⟶ 300 operations in Italy each year(http://www.ospedaleniguarda.it/in-evidenza/leggi/chirurgia-dellepilessia)
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EXISTING TECHNIQUES FOR BRAIN MAPPING
Functional Magnetic Resonance Imaging
PREOPERATIVE
Transcranial Magnetic Stimulation
INTRAOPERATIVE
Direct Cortical Stimulation
Electromagnetic Cortical Stimulation
Safe, non-invasive
Not good for language mappingLow resolution
Simple
InvasiveSeizuresLow penetration depth
Safe, non-invasive
Coil dimensions
Electromagnetic coil
Pulsed magnetic field
Stimulated cortical region
(Ilmoniemi, Ruohonen, and Karhu 1999; Rossi et al. 2009)
(Matz, Cobbs, and Berger 1999; Hervey-Jumper et al. 2015)
(Buzzi et al. 2015; Developed by NearLab, DEIB)
(Gore 2003)
Safe, non-invasive
Big coils (not suitable for intraoperative mapping)
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AIM OF THE WORK
Pulse generator
Stimulation coil
Magnetic wire
B
E −𝜕𝜙 𝐵
𝜕𝑡= ∆𝑉 → 𝑖𝑓 ∆𝑉 > 𝑉𝑠𝑝𝑖𝑘𝑒 → 𝑠𝑝𝑖𝑘𝑒
FEASIBILITY STUDY of an alternative toolfor the intraoperative cortical mapping.
Pulse generator
B
𝑖 → 𝐵 →
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REQUIREMENTS
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BPulse generator
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DIRECT CORTICAL STIMULATION
PULSE SHAPE
AWAKE PATIENT
Penfield protocol:- Current: 2-6 mA- Pulse width: 1 ms- Frequency: 50–60 Hz
ANESTHETIZED PATIENT
Train-of-five protocol:- Current: 4.9-8 mA- Pulse width: 200–500 µs- Frequency: 250–500 Hz
(Matz, Cobbs, and Berger 1999; Hervey-Jumper et al. 2015)
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TRANSCRANIAL MAGNETIC STIMULATION
BIPHASIC
Electric field: 70÷140 V/m
Current: 2-8 kAPulse width: 200–600 µs
PULSE SHAPE
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
MONOPHASIC
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
(Ilmoniemi, Ruohonen, and Karhu 1999; Rossi et al. 2009)
Electromagnetic coil
Pulsed magnetic field
Stimulated cortical region
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ELECTROMAGNETIC CORTICAL STIMULATOR
Current: 32 APulse width: 80 µs
Electric field: 1 V/m
PULSE SHAPE
80 µs 80 µs 80 µs
25 ms 25 ms 90 ms 140 ms
Coil current
Electric field
NOT ENOUGH TO STIMULATE
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REQUIREMENTS
KANTHAL A-1 (FeCrAl alloy)
wires of ϕ = 0.4 mm
- FLEXIBLE- HIGH PERMEABILITY- HIGH SATURATION
MAGNETIC MATERIAL
BPulse
generator
STIMULATION COIL
𝑙 = 3 𝑐𝑚𝜙𝑖𝑛𝑡 = 0.9 𝑐𝑚𝜙𝑒𝑥𝑡 = 2.7 𝑐𝑚𝑁 = 292𝜙𝑤𝑖𝑟𝑒 = 0.82 𝑚𝑚𝜙𝑖𝑛𝑡
𝜙𝑒𝑥𝑡
𝑙
𝑅 =𝜌𝑙
𝑆= 0.5 Ω
𝐿 = 509 𝜇𝐻
CIRCUIT PARAMETERS 𝑑 = 3 𝑚𝑚
𝐿𝑇𝑂𝑇 = 20 𝑐𝑚𝜙𝑐𝑜𝑟𝑒 = 7 𝑚𝑚
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PERFORMANCE EVALUATION
1) Stimulation coil current.
2) Core material: static properties.
3) Core material: dynamic properties
⟶ Comparison with MATLAB simulations
4) Test of the magnetic circuit
⟶ Comparison with COMSOL simulations
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BPulse generator
EXPERIMENTAL PROTOCOL
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1) STIMULATION COIL CURRENT
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2) KANTHAL A-1 – STATIC PROPERTIES
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2) KANTHAL A-1 – STATIC PROPERTIES
Field along the wire
Coercive field
Virgin 𝐻𝑐 = 5.2 𝑂𝑒Positive 𝐻𝑐1 = −4.43 𝑂𝑒Negative 𝐻𝑐2 = 5.95 𝑂𝑒
Retentivity 50 mT
Saturation 𝑀𝑠𝑎𝑡 = 971 𝑘𝐴/𝑚
𝐻𝑠𝑎𝑡 = 100 𝑂𝑒
Loop squareness𝑚𝑟/𝑚𝑠𝑎𝑡
3.74%
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2) KANTHAL A-1 – STATIC PROPERTIES
𝑩 = 𝜇0 𝑯+𝑴(𝑯) = 𝜇0 𝜇𝑟𝑯Pulse
generatorB
Coil Magnetic material
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2) KANTHAL A-1 – STATIC PROPERTIES
Maximum relative permeability ⟶ 80
Saturation ⟶ 100 Oe
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3) KANTHAL A-1 – DYNAMIC PROPERTIES
STIMULATION CURRENT
𝑓 = 100 𝐻𝑧𝐼0 = 3.2 𝐴
Pick-up coil
PICK-UP COIL
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
Up to saturationStimulation coil
Kanthal A-1
𝐵
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3) KANTHAL A-1 – DYNAMIC PROPERTIES
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EXPERIMENTAL DATA SIMULATION DATA (MATLAB)
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3) KANTHAL A-1 – DYNAMIC PROPERTIES
𝑩 = 𝜇0 𝑯+𝑴
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
𝑒𝑚𝑓 = −𝜕𝜙 𝜇0𝐻
𝜕𝑡+𝜕𝜙 𝜇0𝑀
𝜕𝑡
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4) MAGNETIC CIRCUIT
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Kanthal A-1Stimulation coil
Pick-up coil
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4) MAGNETIC CIRCUIT – FREQUENCY
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Kanthal A-1Stimulation coil
Pick-up coil
𝑓 = 37 𝐻𝑧 , 𝐼0 = 3.2 𝐴
COMSOL SIMULATION
EXPERIMENTAL DATA
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4) MAGNETIC CIRCUIT – STIMULATOR
𝐸𝑚𝑎𝑥 = 0.06 𝑉/𝑚
NOT ENOUGH TO STIMULATE
OPTIMIZATIONS:
- MAGNETIC MATERIAL- GEOMETRY
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Kanthal A-1Stimulation coil
Pick-up coil
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OPTIMIZATION OF THE MATERIAL
MATERIAL 𝝁𝒓 𝑯𝒔𝒂𝒕 [𝑨/𝒎]
Metglas nano finemet 50 hz nofieldannealed 100000 10
Metglas nano nanocrystalline viproterm 50 Hz 30000 50
Nickel steel 4750 70000 10
Nickel steel permalloy NGO 50000 10
Nickel steel molypermalloy 70000 20
Stainless steel 430 annealed 800 1000
Stainless steel annealed sus 403 300 2000
Stainless steel 455 annealed 300 5000
Stainless steel chrome 35% steel 80 9000
Kanthal A-1 80 7960
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OPTIMIZATION OF THE GEOMETRY
𝐸ma𝑥 = 30 𝑉/𝑚 ~ 𝐸𝑠𝑡𝑖𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 70 − 140 𝑉/𝑚
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CONCLUSIONS
• Agreement among experimental set-up, simulations and theory
⟶ EXPERIMENTAL PROTOCOL VALIDATION
• Identification of critical parameters:
Saturation, magnetic core material, stimulation circuit
• FEASIBILITY of a magnetic stimulator through magnetic circuit
THANK YOU FOR THE ATTENTION!
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FURTHER DEVELOPMENT
- Perform new simulations
- Core material
- Geometry
- Realize and test a new prototype
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DIRECT CORTICAL STIMULATION
PULSE SHAPE
AWAKE PATIENT
- Current: 2-6 mA- Pulse width: 1 ms
ANESTHETIZED PATIENT
- Current: 4.9-8 mA- Pulse width: 200–500 µs
SPATIAL RESOLUTION ANDPENETRATION DEPTH
- Spatial resolution: up to 0.5 cm- Penetration depth: up to 0.8 cm
Amplitude
Distance
Amplitude
Distance
MONOPOLAR
BIPOLAR
(Matz, Cobbs, and Berger 1999; Hervey-Jumper et al. 2015)
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TRANSCRANIAL MAGNETIC STIMULATION
BIPHASIC
Electric field: 70÷140 V/m
Current: 2-8 kAPulse width: 200–600 µs
PULSE SHAPE𝑒𝑚𝑓 = −
𝜕𝜙 𝐵
𝜕𝑡
MONOPHASIC
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
SPATIAL RESOLUTION ANDPENETRATION DEPTH
- Spatial resolution: up to 0.5 cm- Penetration depth: up to 3 cm
(Ilmoniemi, Ruohonen, and Karhu 1999; Rossi et al. 2009)
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5) MAGNETIC CIRCUIT DESIGN
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B δ
MAGNETIC CIRCUIT DESIGN
𝐵𝑔𝑎𝑝 =𝑁𝑖𝜇0
𝑙𝑐𝑜𝑟𝑒𝜇𝑟
+ 𝛿
+
-
MMF𝜙
ℛ𝑐𝑜𝑟𝑒
ℛ𝑔𝑎𝑝
DESIGN STEPS- Core material- Coil design
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4) MAGNETIC CIRCUIT – STATIC
STIMULATION CURRENT ⟶ 𝐼0 = 4 𝐴
AIR GAP DIMENSION ⟶ 𝑑 = 3𝑚𝑚
MAGNETIC FIELD SENSOR ⟶ Hall effect sensor
𝑩𝒎𝒆𝒂𝒔 𝑩𝒕𝒉𝒆𝒐
50 𝑚𝑇 55 𝑚𝑇
GOOD AGREEMENT
𝐼0 = 20 𝐴 → 𝐵𝑡ℎ𝑒𝑜 = 250 𝑚𝑇
Kanthal A-1
Hall effect sensor
Stimulation coil
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KANTHAL A-1 – STATIC PROPERTIES
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3) ELECTRIC FIELD EVALUATION
𝐸 =𝑒𝑚𝑓
𝑛 ∙ 2𝜋𝑟
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡
INDUCTION’S LAW
PICK-UP COIL
𝑩
𝑬𝒅𝑩
𝒅𝒕
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3) PICK-UP COIL CALIBRATION
PICK-UP COIL
𝑛 = 100𝜙𝑖𝑛𝑡 = 10.1 𝑚𝑚𝜙𝑒𝑥𝑡 = 12.1 𝑚𝑚
𝑅 = 7 Ω
𝑒𝑚𝑓 = −𝜕𝜙 𝐵
𝜕𝑡= −𝐴𝑒𝑓𝑓
𝜕𝐵
𝜕𝑡→ 𝐴𝑒𝑓𝑓 = −
𝑒𝑚𝑝𝑒𝑥𝑝𝜕𝐵𝑡ℎ𝑒𝑜𝜕𝑡
Experimental Geometrical approximation
(9.123 ± 1.23) ∙ 10−3𝑚2 𝑛𝜋𝑟𝑚𝑒𝑎𝑛2 = 9.503 ∙ 10−3 𝑚2
CALIBRATION
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