Upcoming Milestones. Correlate high-resolution and spectroscopic OCT data with cellular ... (CARS) spectroscopy, to produce a versatile system capable of ...
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0= 800 nm
Nonlinear Interferometric Vibrational Imaging (NIVI)
Improving Optical Bandwidth & Axial Resolution
Optical Coherence Tomography
While there are many diagnostic modalities that have been employed for disease detection, such as x-rays, computed tomography, ultrasound, and magnetic resonance imaging, none of these solutions combine the versatility, resolution, size, or weight to be one of the few diagnostic instruments on long-term space flights. Any such system will need to be compact, noninvasive, and be able to image a wide variety of tissues. Also, it will need to have intelligence to aid the diagnostic process because medical specialists will not always be available. Additionally, it would be desirable if such a system could also deliver treatment by altering tissue and be able to monitor the outcome of the treatment.
Optical coherence tomography (OCT) is an emerging biomedical imaging technology that can perform high-resolution imaging of tissue microstructure and function. OCT is analogous to ultrasound imaging, except reflections of near-infrared light are detected rather than sound. OCT can perform "optical biopsies" of tissue, in situ, and in real-time at resolutions comparable to histopathology. Despite the integration of OCT into multiple medical and biological disciplines, imaging has relied on architectural differences within tissue, often limiting the diagnostic capability of this technology.
We present the ongoing development of a new instrument that we call Non-linear Interferometric Vibrational Imaging (NIVI). NIVI integrates and extends several imaging technologies, including OCT, spectroscopic OCT imaging, and Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy, to produce a versatile system capable of noninvasively measuring micron-scale structure and molecular composition of tissues. By performing nonlinear interferometric vibrational imaging of specific molecules, we intend to identify and map the presence of biomolecular precursors to cancer. Using the high-energy pulses generated with this system, we intend to perform cell and tissue ablation of pathological sites, as well as follow-up monitoring of recurrence.
Interferogram between reference and sample CARS
Cross-sectional image of benzene filled cuvette
Axial resolution in OCT depends inversely on spectral bandwidth
Coherent CARS beam is generated in both reference and sample arm and used to generate a molecule-specific image
lc = Coherence length
o = Center wavelength
= Bandwidth (FWHM)
Axial: ~200 m
Transverse: ~20 m
En face images of benzene filled cuvette
Spectral Broadening in ultra-high numerical aperture (UHNA) Fiber
lc 2 m
lc 7 m
Pump: Titanium:sapphire, (810 ± 20) nm, 500 mW avg power, lc 7 m
Output: UHNA fiber, (780 ± 70) nm,
100 mW avg power, lc 2 m
Optical Ranging in Biological Tissue
lc >> m
lc < m
Short Coherence Length
Long Coherence Length
Low-Coherence Interferometry. OCT performs optical ranging in biological tissues. Low-coherence interferometry using a Michelson-type interferometer is a means by which the precise location of a reflection can be determined. An optical source such as a superluminescent diode or a mode-locked laser is used to produce low-coherence light.
Spectroscopic Optical Coherence Tomography
Mach-Zehnder Beam Geometry
Laser System Schematic
New Proposed High Signal Efficiency- Mach-Zehnder Setup
• Construct a unique laser system capable of high-resolution OCT,
spectroscopic OCT, and coherent anti-Stokes Raman scattering
• Improve OCT imaging resolution by generating supercontinuum
light in pumped optical fibers.
• Develop spectroscopic OCT techniques to identify variations in
scattering and absorption.
• Perform morphological and spectroscopic OCT imaging of in vitro
High quality IR achromatic microscope objective
Carrier Spectrum: Spectroscopic OCT
Spectral Reflection / Scattering
Envelope: Amplitude OCT
Reflectivity / Scattering
Object on 3-D Translator
Spectroscopic OCT extracts the spectral information content from the interferogram fringes along each axial scan. A moving windowed Fourier or Morlet Wavelet transform can be used to obtain the spectrum of the light being reflected at each interface. An in vivo demonstration of this technique is shown to the left. This image was taken of a Xenopus leavis (African Frog) tadpole.
Pump: 800 nm
J Regen. Amp.
Stokes: 850-2300 nm
Path delay compensation
(Centroid color code)
A combination of lasers is needed to generate high-energy pulses to perform OCT, induce nonlinear effects for CARS, and to ablate cells and tissue. A diode-pumped solid state laser (DPSS) is used to pump a titanium:sapphire oscillator which in-turn seeds a regenerative amplifier. Ultra-short pulses (50-100 fs) are amplified to hundreds of nanojoules. Output from the regen is split. These high-energy pulses can be used to ablate cells. Half of the regen output is sent through a stretcher-compressor and to an optical parametric amplifier (OPA). This system is tunable over the range of 850-2300 nm. The two beams are re-combined and sent to a free-space interferometer for Nonlinear Interferometric Vibrational Imaging (NIVI).
50/50 beamsplitter (can be a cube)
Anti-stokes absorption filters
Spatial filter is a lens/pinhole combination
Path delay compensation and dither
(Normalized to laser centroid)
(Normalized and noise thresholded)
CCD Image of interference pattern
Daniel Marks1, Selezion Hambir2, Claudio Vinegoni1, Jeremy Bredfeldt1, Chenyang Xu1, Jian Ye1
Amy Wiedemann3, Dana Dlott2, Martin Gruebele2, Barbara Kitchell3, Stephen A. Boppart4
1Department of Electrical and Computer Engineering; 2Department of Chemistry;
3Department of Veterinary Oncology; 4Department of Electrical and Computer Engineering, Bioengineering, College of Medicine
University of Illinois at Urbana-Champaign
Coherent anti-Stokes Raman Scattering (CARS)
Measurement of CARS Interference
Pump: 800nm 80mW
Stokes: 1056nm 5mW
CARS: 655nm ~mW Species: Benzene
p = pump laser frequency
s = Stokes laser frequency
AS = anti-Stokes output frequency
CARS= 2pump- Stokes
Tune frequency difference (p - s) to match
molecular vibrational levels (|1> and |0>)
CARS Spectroscopy of
Tumor Cell Populations
We have produced the first demonstration of mutually interfered, independently generated
CARS signals in non-gaseous media. Phase coherence is indeed preserved (and is stable)
between two separately generated CARS signals, despite the potential of self-focusing,
self-phase-modulation, and other undesirable nonlinear effects.
Feline Fibrosarcoma, 25000 cells/l
Canine Fibrosarcoma, 55000 cells/l
Cross-section of interference pattern
Pump = 527 nm, Stokes = 628.4 nm, Shift 3060 cm-1
Biophotonics Imaging Laboratory
This work was supported by NASA and the National Institutes of Health (NCI)