Stimulated Raman scattering spectroscopic optical coherence tomography

Abstract

We integrate spectroscopic optical coherence tomography (SOCT) with stimulated Raman scattering (SRS) to enable simultaneously multiplexed spatial and spectral imaging with sensitivity to many endogenous biochemical species that play an important role in biology and medicine. The combined approach, termed SRS-SOCT, overcomes the limitations of each individual method. Ultimately, SRS-SOCT has the potential to achieve fast, volumetric, and highly sensitive label-free molecular imaging. We demonstrate the approach by imaging excised human adipose tissue and detecting the lipids’ Raman signatures in the high-wavenumber region.

Coherently broadened, high-repetition-rate laser for stimulated Raman scattering–spectroscopic optical coherence tomography

“…Stimulated Raman scattering–spectroscopic optical coherence tomography (SRS-SOCT) is a recently developed molecular imaging technique that leverages the spatial and spectral multiplexing capabilities of SOCT with the molecular sensitivity and specificity of SRS for fast, tomographic, and label-free molecular imaging [1,2]. To date, SRS-SOCT, as well as other nonlinear, dispersion-based methods [1-4], have relied on a low repetition (rep.) rate, regeneratively amplified laser source to generate (1) a low-coherence, broadband pulse for low-coherence interferometric detection with (S)OCT and wide coverage of the Raman spectral regions of interest, and (2) a narrowband pulse to coherently drive the nonlinear vibrational interactions with a high spectral resolution. However, low-rep. rate, amplified lasers are not well suited for biological imaging as their high peak powers can easily cause sample damage [5], and the low rep. rate can limit imaging speed.…”

“…After the Stokes and pump beam interact with the sample, the back-reflected sample field can be described as ES(ω)=r⋅E0(ω)×exp[−i⋅truen~NL(ω)⋅ωz0∕c], where truen~NL∝χ(3)(Ω)⋅IStokes is the complex nonlinear refractive index, r is the reflectivity of the sample, z 0 is the region of interaction, I Stokes is the Stokes intensity, and Ω = ω – ω Stokes ; is the wavenumber. The detected interferometric signal between the sample and reference arm, after removing the DC component (which can be achieved digitally) and assuming a single reflector, can be described as [1,2] I~(ω)=rI0(ω)e−i⋅ωc⋅2z×exptrue[z0β0ω2c⋅Im{χ(3)(Ω)}⋅IStokestrue]×exptrue[−iz0β0ωc⋅Re…”

Multi-modal Nonlinear Optical and Thermal Imaging Platform for Label-Free Characterization of Biological Tissue

“…Several groups have demonstrated selective combinations of nonlinear imaging strategies to address a range of biological questions, in vitro and in vivo ( 10 ), particularly sensing fast biological processes such as neuronal action potentials and calcium activity with combined SRS and calcium-sensitive MPF ( 9 ). Integration of SRS with optical coherence tomography (OCT) has been shown to augment nonspecific scattering-based contrast with vibrational specificity to image lipid distributions in excised human adipose tissue ( 11 ). More recently, researchers have employed four or more nonlinear imaging modalities, including CARS, MPF, SHG, and third harmonic generation for live tissue and intravital imaging towards wound healing and cancer metastasis ( 12 , 13 ).…”

“…The ability to sense neuronal membrane potential and calcium activity with combined SRS and calcium-sensitive MPF has been demonstrated to show the capacity of SRS for label-free sensing of neuronal action potentials (24,25). Integration of SRS with optical coherence tomography (OCT) has been shown to augment nonspecific scattering-based contrast with vibrational specificity to image lipid distributions in excised human adipose tissue (37,38). More recently, researchers have employed four or more nonlinear imaging modalities, including CARS, MPF, SHG, and third harmonic generation for live tissue and intravital imaging towards wound healing and cancer metastasis (26,27,39).…”

Multi-modal nonlinear optical and thermal imaging platform for label-free characterization of biological tissue

“…Several groups have demonstrated selective combinations of nonlinear imaging strategies to address a range of biological questions, in vitro and in vivo 10 , particularly sensing fast biological processes such as neuronal action potentials and calcium activity with combined SRS and calcium-sensitive MPF 9 . Integration of SRS with optical coherence tomography (OCT) has been shown to augment nonspecific scattering-based contrast with vibrational specificity to image lipid distributions in excised human adipose tissue 11 . More recently, researchers have employed four or more nonlinear imaging modalities, including CARS, MPF, SHG, and third harmonic generation for live tissue and intravital imaging towards wound healing and cancer metastasis 12 , 13 .…”