Inverse Spectroscopic Optical Coherence Tomography Research Articles

Inverse spectroscopic optical coherence tomography (IS-OCT) for characterization of particle size and concentration

Inverse spectroscopic optical coherence tomography (IS-OCT) methods apply inverse problem formulations to acquired spectra to estimate depth-resolved sample properties. In the current study, we modelled the time-frequency-distributions using Lambert-Beer’s law and implemented IS-OCT using backscattering spectra calculated from Mie theory, then demonstrated the algorithm on polystyrene microspheres under idealized conditions. The results are significant because the method generates depth dependent estimates of both the concentration and diameter of scattering particles.

Measuring light scattering and absorption in corals with Inverse Spectroscopic Optical Coherence Tomography (ISOCT): a new tool for non-invasive monitoring

The success of reef-building corals for >200 million years has been dependent on the mutualistic interaction between the coral host and its photosynthetic endosymbiont dinoflagellates (family Symbiodiniaceae) that supply the coral host with nutrients and energy for growth and calcification. While multiple light scattering in coral tissue and skeleton significantly enhance the light microenvironment for Symbiodiniaceae, the mechanisms of light propagation in tissue and skeleton remain largely unknown due to a lack of technologies to measure the intrinsic optical properties of both compartments in live corals. Here we introduce ISOCT (inverse spectroscopic optical coherence tomography), a non-invasive approach to measure optical properties and three-dimensional morphology of living corals at micron- and nano-length scales, respectively, which are involved in the control of light propagation. ISOCT enables measurements of optical properties in the visible range and thus allows for characterization of the density of light harvesting pigments in coral. We used ISOCT to characterize the optical scattering coefficient (μs) of the coral skeleton and chlorophyll a concentration of live coral tissue. ISOCT further characterized the overall micro- and nano-morphology of live tissue by measuring differences in the sub-micron spatial mass density distribution (D) that vary throughout the tissue and skeleton and give rise to light scattering, and this enabled estimates of the spatial directionality of light scattering, i.e., the anisotropy coefficient, g. Thus, ISOCT enables imaging of coral nanoscale structures and allows for quantifying light scattering and pigment absorption in live corals. ISOCT could thus be developed into an important tool for rapid, non-invasive monitoring of coral health, growth and photophysiology with unprecedented spatial resolution.

Detection of Malignancy in Ocular Surface Lesions by Inverse Spectroscopic Optical Coherence Tomography and Two-Photon Autofluorescence.

PurposeAdvanced imaging is increasingly important in the diagnosis of ocular surface malignancy. Inverse spectroscopic optical coherence tomography (ISOCT) and two-photon autofluorescence microscopy (2P-AF) are emerging techniques capable of quantifying ultrastructural and metabolic changes, respectively. We aimed to detect malignancy in ocular surface lesions using ISOCT and 2P-AF.MethodsPortions of excised specimens from patients undergoing conjunctival biopsy at Boston Medical Center were imaged by ISOCT and/or 2P-AF, and submitted for histologic diagnosis. Lesions were categorized as malignant, premalignant (with dysplasia) or benign. ISOCT and 2P-AF findings were compared between categories.ResultsFourteen specimens from 13 patients were collected. The IS-OCT marker D was 2.2-fold higher in combined malignant and premalignant (4.27 ± 0.28, n = 3) versus benign (1.92 ± 0.26, n = 11) lesions (P = 9 × 10−4). ISOCT markers μs and μb were not significantly different. By 2P-AF, the redox ratio was 0.24-fold lower in premalignant (0.11 ± 0.004, n = 2) versus benign (0.45 ± 0.04, n = 9) lesions (P = 1.08 × 10−5).ConclusionsConjunctival lesions with higher malignant potential had higher D and lower redox ratios. Higher D can correlate with ultrastructural changes associated with malignancy, similar to what has been seen in cancers of the gut mucosa. Lower redox ratios can suggest the presence of the Warburg effect, which is associated with tumorigenesis.Translational RelevanceIS-OCT and 2P-AF can potentially be applied to the detection of malignancy or malignant potential in ocular surface lesions. ISOCT allows for the detection of nanoscale ultrastructural changes that are not resolvable by conventional OCT.

Single capillary oximetry and tissue ultrastructural sensing by dual-band dual-scan inverse spectroscopic optical coherence tomography

Measuring capillary oxygenation and the surrounding ultrastructure can allow one to monitor a microvascular niche and better understand crucial biological mechanisms. However, capillary oximetry and pericapillary ultrastructure are challenging to measure in vivo. Here we demonstrate a novel optical imaging system, dual-band dual-scan inverse spectroscopic optical coherence tomography (D2-ISOCT), that, for the first time, can simultaneously obtain the following metrics in vivo using endogenous contrast: (1) capillary-level oxygen saturation and arteriolar-level blood flow rates, oxygen delivery rates, and oxygen metabolic rates; (2) spatial characteristics of tissue structures at length scales down to 30 nm; and (3) morphological images up to 2 mm in depth. To illustrate the capabilities of D2-ISOCT, we monitored alterations to capillaries and the surrounding pericapillary tissue (tissue between the capillaries) in the healing response of a mouse ear wound model. The obtained microvascular and ultrastructural metrics corroborated well with each other, showing the promise of D2-ISOCT for becoming a powerful new non-invasive imaging tool.

Enhanced Survival with Implantable Scaffolds That Capture Metastatic Breast Cancer Cells In Vivo.

The onset of distant organ metastasis from primary breast cancer marks the transition to a stage IV diagnosis. Standard imaging modalities often detect distant metastasis when the burden of disease is high, underscoring the need for improved methods of detection to allow for interventions that would impede disease progression. Here, microporous poly(ε-caprolactone) scaffolds were developed that capture early metastatic cells and thus serve as a sentinel for early detection. These scaffolds were used to characterize the dynamic immune response to the implant spanning the acute and chronic foreign body response. The immune cell composition had stabilized at the scaffold after approximately 1 month and changed dramatically within days to weeks after tumor inoculation, with CD11b(+)Gr1(hi)Ly6C(-) cells having the greatest increase in abundance. Implanted scaffolds recruited metastatic cancer cells that were inoculated into the mammary fat pad in vivo, which also significantly reduced tumor burden in the liver and brain. Additionally, cancer cells could be detected using a label-free imaging modality termed inverse spectroscopic optical coherence tomography, and we tested the hypothesis that subsequent removal of the primary tumor after early detection would enhance survival. Surgical removal of the primary tumor following cancer cell detection in the scaffold significantly improved disease-specific survival. The enhanced disease-specific survival was associated with a systemic reduction in the CD11b(+)Gr1(hi)Ly6C(-) cells as a consequence of the implant, which was further supported by Gr-1 depletion studies. Implementation of the scaffold may provide diagnostic and therapeutic options for cancer patients in both the high-risk and adjuvant treatment settings. Cancer Res; 76(18); 5209-18. ©2016 AACR.

Detection of extracellular matrix modification in cancer models with inverse spectroscopic optical coherence tomography

In cancer biology, there has been a recent effort to understand tumor formation in the context of the tissue microenvironment. In particular, recent progress has explored the mechanisms behind how changes in the cell-extracellular matrix ensemble influence progression of the disease. The extensive use of in vitro tissue culture models in simulant matrix has proven effective at studying such interactions, but modalities for non-invasively quantifying aspects of these systems are scant. We present the novel application of an imaging technique, Inverse Spectroscopic Optical Coherence Tomography, for the non-destructive measurement of in vitro biological samples during matrix remodeling. Our findings indicate that the nanoscale-sensitive mass density correlation shape factor D of cancer cells increases in response to a more crosslinked matrix. We present a facile technique for the non-invasive, quantitative study of the micro- and nano-scale structure of the extracellular matrix and its host cells.

Fractal Characterization of Chromatin Decompaction in Live Cells

Chromatin organization has a fundamental impact on the whole spectrum of genomic functions. Quantitative characterization of the chromatin structure, particularly at submicron length scales where chromatin fractal globules are formed, is critical to understanding this structure-function relationship. Such analysis is currently challenging due to the diffraction-limited resolution of conventional light microscopy. We herein present an optical approach termed inverse spectroscopic optical coherence tomography to characterize the mass density fractality of chromatin, and we apply the technique to observe chromatin decompaction in live cells. The technique makes it possible for the first time, to our knowledge, to sense intracellular morphology with length-scale sensitivity from ∼30 to 450 nm, thus primarily probing the higher-order chromatin structure, without resolving the actual structures. We used chromatin decompaction due to inhibition of histone deacytelases and measured the subsequent changes in the fractal dimension of the intracellular structure. The results were confirmed by transmission electron microscopy and confocal fluorescence microscopy.

In vivo capture and label-free detection of early metastatic cells.

Breast cancer is a leading cause of death for women, with mortality resulting from metastasis. Metastases are often detected once tumor cells affect the function of solid organs, with a high disease burden limiting effective treatment. Here we report a method for the early detection of metastasis using an implanted scaffold to recruit and capture metastatic cells in vivo, which achieves high cell densities and reduces the tumor burden within solid organs 10-fold. Recruitment is associated with infiltration of immune cells, which include Gr1hiCD11b+ cells. We identify metastatic cells in the scaffold through a label-free detection system using inverse-spectroscopic optical coherence tomography, which identifies changes to nanoscale tissue architecture associated with the presence of tumor cells. For patients at risk of recurrence, scaffold implantation following completion of primary therapy has the potential to identify metastatic disease at the earliest stage, enabling initiation of therapy while the disease burden is low.

Spatially resolved optical and ultrastructural properties of colorectal and pancreatic field carcinogenesis observed by inverse spectroscopic optical coherence tomography

Field carcinogenesis is the initial stage of cancer progression. Understanding field carcinogenesis is valuable for both cancer biology and clinical medicine. Here, we used inverse spectroscopic optical coherence tomography to study colorectal cancer (CRC) and pancreatic cancer (PC) field carcinogenesis. Depth-resolved optical and ultrastructural properties of the mucosa were quantified from histologically normal rectal biopsies from patients with and without colon adenomas (n=85) as well as from histologically normal peri-ampullary duodenal biopsies from patients with and without PC (n=22). Changes in the epithelium and stroma in CRC field carcinogenesis were separately quantified. In both compartments, optical and ultra-structural alterations were consistent. Optical alterations included lower backscattering (μb) and reduced scattering (μs') coefficients and higher anisotropy factor g. Ultrastructurally pronounced alterations were observed at length scales up to ∼450 nm, with the shape of the mass density correlation function having a higher shape factor D, thus implying a shift to larger length scales. Similar alterations were found in the PC field carcinogenesis despite the difference in genetic pathways and etiologies. We further verified that the chromatin clumping in epithelial cells and collagen cross-linking caused D to increase in vitro and could be among the mechanisms responsible for the observed changes in epithelium and stroma, respectively.

Imaging a full set of optical scattering properties of biological tissue by inverse spectroscopic optical coherence tomography

We here develop a method to measure and image the full optical scattering properties by inverse spectroscopic optical coherence tomography (ISOCT). Tissue is modelled as a medium with continuous refractive index (RI) fluctuation and such a fluctuation is described by the RI correlation functions. Under the first-order Born approximation, the forward model is established for ISOCT. By measuring optical quantities of tissue including the scattering power of the OCT spectrum, the reflection albedo α defined as the ratio of scattering coefficient μ(s), and the backscattering coefficient μ(b), we are able to inversely deduce the RI correlation function and image the full set of optical scattering properties.