Multimodal optical neural imaging Multimodal optical neural imaging with VCSEL light sources

Techniques in Biophotonic ImagingPh M d bPhotonics Media Webinar

March 21, 2013,

Dr. Ofer LeviInstitute of Biomaterials and Biomedical Engineering

The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto Toronto Ontario M5S 3G9

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University of Toronto, Toronto, Ontario, M5S 3G9

Biophotonics.utoronto.ca

Our research areasWe develop bio-sensors and biomedical imaging systems imaging systems

• Miniature bio-sensors for optical sensing inside Lab-on-a-Chip g pmicro-fluidics chips

• Bio sensors and optical imaging• Bio-sensors and optical imaging systems for portable in vivo i i f l ti it dimaging of neural activity and disease progression applications

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Optical imaging and stimulation

Optical brain imaging and stimulation is minimally invasive

Optical Stimulation

Electrical Stimulationstimulation is minimally invasive

It avoids artifacts in electrical Optical I i

StimulationStimulation

Electrical Recordingrecording or stimulation ImagingRecording

Optical brain imaging Optical brain imaging and stimulation

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Near IR optical imaging

We like to use near IR light for live tissue imagingRelatively cheap high resolution safe Relatively cheap, high resolution, safe, Favorable optical tissue properties

abs ~ 0.04 cm-1 scattering ~ 10 cm-1 60

80

100

(a.u

.)

Excitation Emission

abs scattering

Other benefits• Low tissue auto-fluorescence 600 650 700 750

0

20

40

Inte

nsity

Low tissue auto fluorescence• Increased availability of near IR molecular markers(Cy5.5, IR800, NIR-

600 650 700 750Wavelength (nm)

664, etc.)• Emerging near IR fluorescent proteinsS t f ti h h• Spectroscopy of tissue chromophores(concentration of lipids, water, oxygenation level)

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yg )In vivo imaging review: E. M. Hillman, "Optical brain imaging in vivo: techniques and applications from animal to man," J Biomed Opt 12, 051402 (2007).

blood flow: Laser speckle contrast imagingg g

Speckle is an interference phenomenon: Constructive/ destructive interference of diffusely reflected lightdestructive interference of diffusely reflected light

• SPECKLE PATTERN results:Dark and light spots seen atdetector

• What if there is movementin the sample?SPECKLE CONTRASTSPECKLE CONTRAST

Calculate dev/mean

Speckle imaging review: D. A. Boas, and A. K. Dunn, "Laser speckle contrast imaging in

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in 5x5 ROIsspeckle contrast imaging in biomedical optics," J. Biomed. Opt. 15, 011109 (2010)

blood oxygenation: Intrinsic optical signal imagingoptical signal imaging

Tissue Oxygen metabolism is studied by multi-wavelength reflectance imaging called Intrinsic Optical Signal imaging reflectance imaging, called Intrinsic Optical Signal imaging

We use 3 wavelengths: 670, 795, 850 nmg , , mApply Beer-Lambert law for concentration changes (< mM)

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H. Levy, D. Ringuette, and O. Levi, "Rapid monitoring of cerebral ischemia dynamics using laser-based optical imaging of blood oxygenation and flow," Biomedical Optics Express 3, 777-791 (2012).

Coherence Modulation: Current Sweeping in a VCSELSweeping in a VCSEL

VCSEL: Vertical Cavity Surface E itti LEmitting Laser• Near lasing threshold, emits as a

single trans erse modesingle transverse mode

• Higher currents excite multiple transverse modestransverse modes

• By rapidly sweeping the operating• By rapidly sweeping the operating current, one can superimpose the laser modes, broadening spectrumlaser modes, broadening spectrum

Result: tuneable coherence

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Result tuneable coherence

VCSEL illumination (spot shape) in the far field regimeg

4.3 mA 5.1 mA 7 mA 9 mA

11 mA 13 mA 17 mA 19 mA

Current sweeping allows a fast sweep ll l between all spatial modes, a reduction of

the coherence effects and creation of a high brightness “LED like” source

a.

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high brightness LED like sourceE. A. Munro, H. Levy, D. Ringuette, T. D. O'Sullivan, and O. Levi, "Multi-modality optical neural imaging using coherence control of VCSELs," Opt. Express 19, 10747-10761 (2011).

Coherence length evaluation

0.9

1.0 1.9 mA7.0 mA 0 9

1.0 2.1 mA 8.0 mA

795 nm0.9

1.0 2.9 mA 9.0 mA

670 nm 850 nm

0.4

0.5

0.6

0.7

0.8

Pow

er (a.

u.)

7.0 mA 2-10 mA

0.4

0.5

0.6

0.7

0.8

0.9

Pow

er (a.

u.)

2-10 mA

0.4

0.5

0.6

0.7

0.8

0.9

Pow

er (a.

u.)

2-12 mA

670.0 670.5 671.0 671.5 672.0 672.5 673.00.0

0.1

0.2

0.3

Wavelength (nm)797.5 798.0 798.5 799.0 799.5 800.0 800.5

0.00.10.20.3P

Wavelength (nm)848.5 849.0 849.5 850.0 850.5 851.0

0.00.10.20.3P

Wavelength (nm)

• Current sweep can broaden VCSEL laser emission spectra integrated 0.8

0.9

1.0 670 nm 795 nm850laser emission spectra, integrated

over ~ few msec. of a camera frame 0 3

0.4

0.5

0.6

0.7

ring

e Visib

ility

850 nm

• Interferograms of sweep mode show

0.0 0.1 0.2 0.3 0.4 0.5 0.60.0

0.1

0.2

0.3Fr

Path Difference (mm)

nterferograms of sweep mode show corresponding reduced coherence, similar for each of 3 wavelengths

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( )

Coherence length:

2044.0

1)2ln(2cLc

Simultaneous IOSI and LSCI680 nm – single modeFast frame by frame

switching between 795 nm – multimode

gdifferent lasers and single / multi-transverse

d ll i i modes allow imaging flexibility

Si l d i i bl d fl (hi h h )

680 nm – multimode 850 nm – multimode

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Single mode – imaging blood flow (high coherence)Multi-mode- imaging tissue oxygenation (low coherence)

Results: LSCI and IOSI

Knot to create a transient ischemia

Grey – Induced ischemia period

11H. Levy et al. Biomedical Optics Express 3, 777-791 (2012).

Vessel ClusteringSimultaneous imaging of blood flow and oxygenation during Ischemia allows automated clustering of veins during Ischemia allows automated clustering of veins and arteries

12H. Levy et al. Biomedical Optics Express 3, 777-791 (2012).

Multi-exposure LCSI- vessel depth discriminationdepth discrimination

Applying multi-exposure technique with VCSELs:• improved flow velocity evaluationp f y• Estimating the contribution of static and dynamic

speckle patterns from skull and tissue - depth di i i i ( 200 )discrimination (~ 200 m)

13Y. Atchia et al. "Rapid Multi-Exposure in-vivo Brain Imaging System using VCSELs as a Light Source" Applied Optics, 52(5): 1041-8 (2013).

Blood Brain Barrier Disruption Imagingg g

Vein/Artery Blood flow ratioA leak in the barrier results in flow reduction in veins

Vein/Artery Blood flow ratio

Vein Vein

Fluorescence

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Blood Brain Barrier Disruption Imagingg g

Comparison of blood flow to fluorescence changesApplication of BBB disrupting drug (DOC) results in Application of BBB disrupting drug (DOC) results in fluorescent marker leakage and flow velocity changes

15S. Dufour et al. “Laser speckle contrast imaging as an intrinsic method to monitor blood brain barrier integrity” in preparation

Multimodal imaging and electrophysiology: Epilepsyp y gy p p y

Multimodal imaging of blood flow, oxygenation and fluorescence is compared to electrophysiology recordingfluorescence is compared to electrophysiology recording

16S. Dufour et al. “Multimodal optical brain imaging for in vivo epilepsy studies”, in preparation

Multi-modality imaging

F d l k l d l h h Forward looking : Our Multi-modality high sensitivity imaging system can be easily

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modified to incorporate brain stimulation

Summary

• Developed a multi-modality optical neural imagingDeveloped a multi modality optical neural imaging

system, using a fast camera and miniature VCSELs

• This imaging system is a fast, versatile, miniature, low

t i i l ti f ti l b i i icost imaging solution for optical brain imaging

• Study the progression and treatment of neurologicalStudy the progression and treatment of neurological

disorders including Ischemic stroke and Epilepsy

• Discussed the path to a portable imaging system, for

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brain imaging in freely-behaving animals

Acknowledgments

Funding agencies : NSERC, CIHR, MITACS, CMC, CIPI

Collaborations:Canada: P. Carlen, B. Stefanovic, T. Valiante, B. Wilson, G. Zheng, W. Whelan

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B. Wilson, G. Zheng, W. Whelan

USA: J. Harris, S. Gambhir