Upload
others
View
27
Download
0
Embed Size (px)
Citation preview
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
1
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
2
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
3
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)
4
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
5
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)
6
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
7
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.
8
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
9
( )
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
10
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
14
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
d f d b l17
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
b i i i i f l b h i i l18
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
19
B. Wilson, G. Zheng, W. Whelan
USA: J. Harris, S. Gambhir