Localization and Assessment of Epileptic FociA new method using Wavelet Packets

With

Itai Doron, Eden Rephaeli (TAU)

Oren Sagher – Dep. Of Neurosurgery, Univ. of Michigan Health System Leo V. Towle – Dep. Of Neurology, Univ. of Chicago Hospitals

Eshel Ben-Jacob (TAU)

Tomer Gazit (BIU & TAU)

Epilepsy Workshop, Michigan, May 9

Outline

• Introduction – the localization problem

• The method • Results

• New insights and conclusions

Voltage

Time

Invasive Recordings - Subdural EEG (ECoG)Invasive Recordings - Subdural EEG (ECoG)

1-3 weeks recordings

Invasive Recordings – Depth ElectrodesInvasive Recordings – Depth Electrodes

1-3 weeks recordings

The Challenge:The Challenge:

Inter-ictal

(before the seizure)

Onset

Ictal

(The seizure)

Localization and assessment of the Epileptic foci

Delta: <3.5 Hz

Theta: 3.5-7 Hz

Alpha: 7-13 Hz

Beta: 13-30 Hz

Gamma: >30 Hz

The Classical Frequency Bands

The Big Picture

Fre

qu

en

cy

0 HZ

42 HZ

Similarity

In all successful surgeries, the method detected the correct foci

Time-Frequency Analysis – Some Math

The Fourier Transform

Time basis Frequency basis

Time Frequency

Voltage Power

Time

Fre

que

ncy

Signal

Time-Frequency

plane

Beyond Fourier Transform

Time-Frequency Analysis

Wavelets

A “mother wavelet”is a function located in time and frequency.

The Mexican Hat

s

ut

ssu 1),(

The function is dilated and time-shifted to form a set of basis functions:

The Coiflet

Binary tree Wavelet basis

The Wavelet Transform

70

31

32

11

12

13

4

98

234567

(70)36

(31)23

(32)13

11

12

(13)9

4

9

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2

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7

Wavelet Packet DecompositionMaximum Information

Best Basis

“Shannon Information” Like

Doron et al. Time-Invariant Person Specific Frequency Templates in Human Brain Activity,PRL. 96 (2006)

3/16 1/16 2/16 4/16

Quantifying the Similarity

ji

ji ji

ji

nnn nn

nnW

PP

PPjiS

,),max(

),min(),(

Wn

n

n

nn MMP

Inter-Ictal Analysis: Similarity Matrices

3224544748 6 884072 8 463856556461607674777578737969685958525143455057444933667034424153261827282011 3 12 1 9 22 2 21193536 4 8314 7 8425178237 5 71868562801310672963153981873123306516

32245447486

8840728

4638565564616076747775787379696859585251434550574449336670344241532618272820113

1219

222

211935364

83147

84251782375

71868562801310672963153981873123306516

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

746879818017677569636261937165594645537770383224233022142131158629434136555456 6 7 13571944 5 202835338547 8 891287494034768452481688 2 501166907891 3 1826 1 6092272510 9 7358835139 4 7264378242

74687981801767756963626193716559464553777038322423302214213115862943413655545667

135719445

2028353385478

8912874940347684524816882

5011669078913

18261

60922725109

73588351394

7264378242

0.1

0.2

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0.9

Type I

Type II

Type I

Type II

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Type I - Comparison

Failed – the focus could not be removed

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Type II- Comparison

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LT 4

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PST 3

PG 17PG 10

PG 3

AST 3RD 4

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PG 9PG 2

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RD 1

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LD 1

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Partially successful

SuccessfulPartially successful

Failed

LT8

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LI6LI5LA6

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Results - 11 Patients

Type I Type II

7 Patients 4 Patients

6 successful surgeries

1 Failed (Focus could not be removed)

1 successful surgery

3 Non-successful

In all the successful surgeries the resected zones matched the predicted foci

In all the non-successful surgeries One (or more) predicted focus was not resected

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PT 14

PT 6

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PT 15

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PT 7

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PT 24

ST 7

PT 16

ST 8

ST 6

PT 8

ST 5

AT 8

ST 4

SF 64

ST 3

SF 56

AT 7

ST 2

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SF 55

AT 6

ST 1AT 1

SF 62

SF 54

AT 5

AT 2AT 3

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SF 61

AT 4

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SF 60

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SF 50

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SF 49SF 57

Type I

Type II

Looking Ahead

Early Warning Epilepsy Pace-Maker

The Iron Age

The patient survived the surgery

The Middle Ages

Can we do better?

Scalp EEG

Dynamics of Multiple Foci – For type II

Summary

New methods for: Localization and Assessments of Epileptic Foci

3. New insights

2. Satisfying agreement with surgery results

1. Identification of two Types of Seizure Dynamics

We do not seek:The “world best method”

and not to replace the Epileptologists

We hope that one day The methods will be used for diagnostics

Thank you