SQUID sensors a SQUID sensors a successful successful

complementary complementary electrophysiological electrophysiological

instrument for imaging instrument for imaging brain and nerve activitiesbrain and nerve activities

Zvonko TronteljZvonko TronteljPhysics Dept., University of LjubljanaPhysics Dept., University of Ljubljana

andandInstitute for Mathematics, Physics and Institute for Mathematics, Physics and

Mechanics, LjubljanaMechanics, Ljubljana

Participating ResearchersParticipating ResearchersUniversity of LjubljanaUniversity of Ljubljana::Vojko Jazbinsek, Matjaz Slibar, Ales Stampfl, Robert Vojko Jazbinsek, Matjaz Slibar, Ales Stampfl, Robert ZorecZorecPTB Berlin:PTB Berlin:Sergio Erné, Sergio Erné, Lutz Trahms, Martin BurghoffLutz Trahms, Martin Burghoff Wolfgang Wolfgang Mueller, Gerd WuebbelerMueller, Gerd Wuebbeler. . FU BerlinFU Berlin: : Gabriel Curio, Peter AustGabriel Curio, Peter AustTU Darmstadt:TU Darmstadt:Gerhard ThielGerhard Thiel, Michael Wacke, Michael WackeVanderbilt University:Vanderbilt University:Franz Baudenbacher, Luis Fong, Jenny Holzer, John Franz Baudenbacher, Luis Fong, Jenny Holzer, John WikswoWikswoProducers of instrumentation: Producers of instrumentation: Neuromag-Electa, CTFNeuromag-Electa, CTF

Outline of talkOutline of talk IntroductionIntroduction On SQUID sensorOn SQUID sensor Measuring systemsMeasuring systems Basic Basic ssteps in data analysis and modelingteps in data analysis and modeling of of

sources of bioelectric activitysources of bioelectric activity Examples:Examples: a)Peripheral nerve studiesa)Peripheral nerve studies bb) ) Some examples of brain studiesSome examples of brain studies ConclusionsConclusions

Objectives:Objectives:

To apply SQUID(s) in order to obtain the To apply SQUID(s) in order to obtain the noninvasive information on:noninvasive information on:

a)a) I Ionic currents in electrically stimulatonic currents in electrically stimulated ed peripheral nerve medianus.peripheral nerve medianus.

b) b) Localizations of epileptical focus.Localizations of epileptical focus.c) c) Localization and functional information on Localization and functional information on

some parts of brain cortexsome parts of brain cortex.. To demonstrate the pre-diagnostic capabilities To demonstrate the pre-diagnostic capabilities

of SQUID(s)of SQUID(s) To model theTo model the intracellular curent (m. field) and intracellular curent (m. field) and

its relation to APits relation to AP

SQUID sensorsSQUID sensors

1.1. What is SQUID?What is SQUID?

2.2. What they offer to us?What they offer to us?

3.3. Where we can use them?Where we can use them?

4.4. Why SQUID sensors in electrophysiology?Why SQUID sensors in electrophysiology?

Ad 1 and Ad 2Ad 1 and Ad 2

Superconducting QUantum Interference DeviceSuperconducting QUantum Interference Device Magnetic flux-to-voltage convertor (the most Magnetic flux-to-voltage convertor (the most

sensitive sensor for quasi dc magnet. fields m.)sensitive sensor for quasi dc magnet. fields m.) Measured m. field; via Amper’s law the sourceMeasured m. field; via Amper’s law the source Based on 3 facts described by QMBased on 3 facts described by QM - superconductivity with Cooper pairs- superconductivity with Cooper pairs - C. pair tunneling- C. pair tunneling - m. flux quantization- m. flux quantization

From Josephson jct. to From Josephson jct. to closed sc. circuitclosed sc. circuit

Dc SQUID configurationDc SQUID configuration

Outer magnetic field is Outer magnetic field is present at the SQUIDpresent at the SQUID

Ad 3 and ad Ad 4Ad 3 and ad Ad 4- M. flux has to be transp.to SQUIDM. flux has to be transp.to SQUID- SQUID has to be in m. shieldedSQUID has to be in m. shielded env. env.- High sensitivity and spatio.temp. r.High sensitivity and spatio.temp. r.

Multichannel SQUID Multichannel SQUID system for brain studiessystem for brain studies

Multichannel SQUID Multichannel SQUID system for brain staudiessystem for brain staudies

Part of SQUIDPart of SQUID microscope and microscope and C.c. C.c. internodal cell holderinternodal cell holder

We measure:We measure: Electric AP Electric AP

KK++ anesthesia anesthesia techniquetechnique

MagneticMagnetic field field SQUID MicroscopeSQUID Microscope

Both measurements Both measurements are simultaneousare simultaneous

SQUID microscope prepared for the SQUID microscope prepared for the C.c. C.c. inernodal cell studies inernodal cell studies (schematically)(schematically)

Basic steps in analysis and Basic steps in analysis and modelling of current modelling of current sources in living mattersources in living matter

Distribution of ionic currents in tissue. ComplicatedDistribution of ionic currents in tissue. Complicated Direct and inverse problemDirect and inverse problem The direct problem – a unique solutionThe direct problem – a unique solution TTZZTTEE

The inverse problem is ill-posed problemThe inverse problem is ill-posed problem EEZZETETTT

Simple geometry – analyt. solutions, Simple geometry – analyt. solutions, otherweise modeling otherweise modeling

Simple geometrySimple geometry

Single cylindrically shaped cell (1D case)Single cylindrically shaped cell (1D case)

Bound. cond.: Bound. cond.: mm(z) = (z) = iia,z) – a,z) – eea,z)a,z)

nn..JJii (a,z) = (a,z) = n n..JJee(a,z)(a,z)

Simple geometry Simple geometry (contin.)(contin.)

From Ampere law:From Ampere law:

BBii = Integr. [G( = Integr. [G(a,z – z’)Ja,z – z’)Jii(a,z’)]dz(a,z’)]dz

Applying the Fourier and the inverse Applying the Fourier and the inverse Fourier transformations one can come Fourier transformations one can come from potential to mag. field and v.a.v.from potential to mag. field and v.a.v.

Some methods in modeling Some methods in modeling of current sourcesof current sources

Current multipole expansionCurrent multipole expansion Current distribution with the minimum norm Current distribution with the minimum norm

estimationestimation Covariance method (to extract the dc Covariance method (to extract the dc

component of the measured modulated component of the measured modulated magnetic field data)magnetic field data)

Part of an axonPart of an axon or(or(C.Corallina C.Corallina intern. Cell): intern. Cell): stimulus location and measuring points; stimulus location and measuring points;

intra-,extracell. curr.; m. fieldintra-,extracell. curr.; m. field

The time evolution of magnetic The time evolution of magnetic field (vert. comp.) measured in field (vert. comp.) measured in 37 points above the 37 points above the C. C. corallinacorallina

Examples:Examples:

Electrically stimulated peripheral Electrically stimulated peripheral nerve medianus. Simultaneus nerve medianus. Simultaneus electrical and magnetic electrical and magnetic measurements. measurements.

Sketch of experimental setupSketch of experimental setup

Mag. field after stimulation at t=0, x=0: a) propagation, Mag. field after stimulation at t=0, x=0: a) propagation, traces at y=30mm, x=285mm, 335mm, 385mmtraces at y=30mm, x=285mm, 335mm, 385mmb) polarity reversal: x=335mm, y= -30mm and 30mmb) polarity reversal: x=335mm, y= -30mm and 30mm

Linear scan of the Linear scan of the magnetic recordings magnetic recordings along thealong the y-axis (a)y-axis (a)

Elec. pot. rec. simult. Elec. pot. rec. simult. at y=0 and x=335mmat y=0 and x=335mm(b)(b)

Isofield pattern in the x’-y plane with 20 fT steps Isofield pattern in the x’-y plane with 20 fT steps between two isofield lines. Crosses indicates the between two isofield lines. Crosses indicates the positins of input data points . The calculated equivalent positins of input data points . The calculated equivalent current dipol is shown.current dipol is shown.

CT cross-section of the right upper arm at x=335mm as CT cross-section of the right upper arm at x=335mm as seen in the distal direction. The encircled dot at the seen in the distal direction. The encircled dot at the edge of median nerve is the position of equivalent cur. edge of median nerve is the position of equivalent cur. dipole.dipole.

The model calculation of the cmpound action currentThe model calculation of the cmpound action current

Results of peripheral nerve study:Results of peripheral nerve study:

The point-like current dipole is a suitable model for a The point-like current dipole is a suitable model for a simple geometry as it is in this case.simple geometry as it is in this case.

The localization of the nerve was within 2 mm (based The localization of the nerve was within 2 mm (based on the CT).on the CT).

Examples:Examples:

Determination of epileptical focus Determination of epileptical focus in the case of focal epilepsyin the case of focal epilepsy

The flowchart of the current approach to The flowchart of the current approach to localizing epileptic focus.  localizing epileptic focus.  A:A: Time domain waveforms showing epileptic Time domain waveforms showing epileptic spikes. spikes. B:B: Spectrogram showing focal increases of Spectrogram showing focal increases of spectral power.spectral power.C:C: Magnetic source image (MSI) showing an Magnetic source image (MSI) showing an epileptic focus. epileptic focus.

SpreadSpread non-normal (epileptic) activitynon-normal (epileptic) activity

The location of epileptical dischargesThe location of epileptical discharges

Examples:Examples:

Study of functional stimulationStudy of functional stimulation

FUNCTIONAL IMAGING: Evoked response to median nerve FUNCTIONAL IMAGING: Evoked response to median nerve stimulation (not clear in the average of MEG sensors (the top stimulation (not clear in the average of MEG sensors (the top overlay) .The earliest peak is from the ACG. Followed by the overlay) .The earliest peak is from the ACG. Followed by the events in the CS. The cerebellum response is seen as well.events in the CS. The cerebellum response is seen as well.

ConclusionsConclusions Magnetic measurements offer also in the world of Magnetic measurements offer also in the world of living living

state state valuable noninvasive information.valuable noninvasive information. Both, Both, multichannel multichannel SQUID system and SQUID SQUID system and SQUID

microscope can be applied. microscope can be applied. The last option offersThe last option offers good good spatial resolutionspatial resolution..

Results from magnetic measurements can be Results from magnetic measurements can be considered considered as as complementary to the existing electric measurements complementary to the existing electric measurements inin many cases. They can be combined with different many cases. They can be combined with different imaging modalities.imaging modalities.

SQUID measurements provide direct information on the SQUID measurements provide direct information on the behavior of ionic currents.behavior of ionic currents.

The highest spatial resolution. The highest spatial resolution.

Thank you for your Thank you for your attention!attention!

Examples from the world of Examples from the world of plants:plants:

a) Simple plant cell – Internodal cell of a) Simple plant cell – Internodal cell of

green algae green algae Chara corallinaChara corallina

Our cell cultureOur cell culture

Chara corallinaChara corallinainternodal cellinternodal cell

Multi-SQUID measuring Multi-SQUID measuring configuration (37 channels) configuration (37 channels) -schematically-schematically

The isofield lines representationThe isofield lines representation

3 particular time values (1.3s, 1.6s, 1.9s) 3 particular time values (1.3s, 1.6s, 1.9s) after the stimulusafter the stimulus

The isof. representation (at 1.4s, 2.5s, 3.6s); The isof. representation (at 1.4s, 2.5s, 3.6s); model. calc. of current dipol and current model. calc. of current dipol and current density along the density along the C.c. C.c. intern. c.intern. c.

Measured and calculated AP and B Measured and calculated AP and B

Some resultsSome results

Spreading of excitation along the cell: v ~ 4cm/sSpreading of excitation along the cell: v ~ 4cm/s

Conductivity:Conductivity:i i = 1.2 = 1.2 -1-1m m -1 -1 , , ex ex = 0.025 = 0.025 -1-1m m -1-1Length of the depolarized area: l ~ 50 mmLength of the depolarized area: l ~ 50 mm Maximal intracellular current: IMaximal intracellular current: I ii = 1 = 1AA

Examples from the world of Examples from the world of plants:plants:

b) the influence of visible light on AP and b) the influence of visible light on AP and oonn B B in in CChara hara ccorallina: orallina: The chemical The chemical nature of AP obtained from the non-nature of AP obtained from the non-invasive observation (by SQUID invasive observation (by SQUID microscope) of the intracellular current microscope) of the intracellular current under the influence of light under the influence of light

Protocol of the Protocol of the C.c.C.c. experimentexperiment with white light illuminationwith white light illumination

• Light OFF reference• Light ON 10 min• Light ON 20 min

• Light ON 60min

AP as function of light exposure

The influence of ilumination on the measured B The influence of ilumination on the measured B and AP of electrically stimulated and AP of electrically stimulated C.c. C.c. internodal internodal cellcell

Model which explains the Model which explains the illumination experiment in the illumination experiment in the context of 2nd messenger systemcontext of 2nd messenger system

[Ca[Ca2+2+]]c c is altered under the influence of light/dark transitions (is altered under the influence of light/dark transitions (Miller@SandersMiller@Sanders 1987) 1987)

AP can be described by an electrically stimulated release of CaAP can be described by an electrically stimulated release of Ca2+2+ from from internal store:internal store:-a) the voltage depend. synthesis/breakdown of the 2nd mesenger IPa) the voltage depend. synthesis/breakdown of the 2nd mesenger IP3 3 . . -b) the joint action of IPb) the joint action of IP3 3 and and CaCa2+2+ on the gating of the receptor channels, on the gating of the receptor channels, which conduct Cawhich conduct Ca2+ 2+ release from internal stores.release from internal stores.-c) modification: cells move excess Cac) modification: cells move excess Ca2+2+ from the cytoplasm back into from the cytoplasm back into internal stores by an endogeneous Cainternal stores by an endogeneous Ca2+2+ pump system (described by the pump system (described by the Hill function.Hill function.

- Quantitative evaluation follows the Othmer model.Quantitative evaluation follows the Othmer model.

Simulated [CaSimulated [Ca+2+2]]c c transients in response to a transients in response to a single electrical stimulationsingle electrical stimulation

SomeSome results results

Assuming that the activation of the ClAssuming that the activation of the Cl- - channels, that cause the depolarization,channels, that cause the depolarization,

is the direct consequence of the change is the direct consequence of the change in [Cain [Ca2+2+]]c c , , the measurementsthe measurements

quantitavely agree well with the model.quantitavely agree well with the model.

Examples from the world of Examples from the world of plants:plants:

c) the injury induced ionic currents in c) the injury induced ionic currents in the plant organs - leaves in the the plant organs - leaves in the higher developed plant higher developed plant Vicia fabaVicia faba, , detected magnetically by the detected magnetically by the multichannel SQUID systemmultichannel SQUID system..

Measuring setupMeasuring setup

The position of injury (panel B cut)The position of injury (panel B cut)

Time evolution of magnetic field in all channels:Time evolution of magnetic field in all channels:panel A 15 min. before injury, panel B 1-16 min after injury, panel A 15 min. before injury, panel B 1-16 min after injury, panel C time evolution of field RMS value, panels D end E panel C time evolution of field RMS value, panels D end E isofield maps 10 min before and 1.5 min after injury.isofield maps 10 min before and 1.5 min after injury.

Some resultsSome results

All measured injured All measured injured Vicia f. Vicia f. plants responded to plants responded to

injuries with detectable quasi-d.c. magnetic signals.injuries with detectable quasi-d.c. magnetic signals. Large injury leads to easily localizable current source Large injury leads to easily localizable current source

of dipolar pattern. The characteristic time delay is of dipolar pattern. The characteristic time delay is

about 10 min.about 10 min. No long-distance spreading of electrical activity wasNo long-distance spreading of electrical activity was

generally observed.generally observed.

The flowchart of the current approach to localizing epileptic focus. The flowchart of the current approach to localizing epileptic focus.   A:A: Time domain waveforms showing epileptic spikes. Time domain waveforms showing epileptic spikes. B:B: Spectrogram showing focal increases of spectral power. Spectrogram showing focal increases of spectral power.C:C: Magnetic source image (MSI) showing an epileptic focus. Magnetic source image (MSI) showing an epileptic focus.