Polarization sensitive optical frequency domain imaging system for endobronchial imaging

A polarization sensitive endoscopic optical frequency domain imaging (PS-OFDI) system with a motorized distal scanning catheter is demonstrated. It employs a passive polarization delay unit to multiplex two orthogonal probing polarization states in depth, and a polarization diverse detection unit to detect interference signal in two orthogonal polarization channels. Per depth location four electro-magnetic field components are measured that can be represented in a complex 2×2 field matrix. A Jones matrix of the sample is derived and the sample birefringence is extracted by eigenvalue decomposition. The condition of balanced detection and the polarization mode dispersion are quantified. A complex field averaging method based on the alignment of randomly pointing field phasors is developed to reduce speckle noise. The variation of the polarization states incident on the tissue due to the circular scanning and catheter sheath birefringence is investigated. With this system we demonstrated imaging of ex vivo chicken muscle, in vivo pig lung and ex vivo human lung specimens

Multimodal probe for optical coherence tomography epidetection and micron-scale indentation

We present a multimodal ferrule-top sensor designed to perform the integrated epidetection of Optical Coherence Tomography (OCT) depth-profiles and micron-scale indentation by all-optical detection. By scanning a sample under the probe, we can obtain structural cross-section images and identify a region-of-interest in a nonhomogeneous sample. Then, with the same probe and setup, we can immediately target that area with a series of spherical-indentation measurements, in which the applied load is known with a μN precision, the indentation depth with sub-μm precision and a maximum contact radius of 100μm. Thanks to the visualization of the internal structure of the sample, we can gain a better insight into the observed mechanical behavior. The ability to impart a small, confined load, and perform OCT A-scans at the same time, could lead to an alternative, high transverse resolution, Optical Coherence Elastography (OCE) sensor

High resolution combined molecular and structural optical imaging of colorectal cancer in a xenograft mouse model

With the emergence of immunotherapies for cancer treatment, there is a rising clinical need to visualize the tumor microenvironment (TME) non-invasively in detail, which could be crucial to predict the efficacy of therapy. Nuclear imaging techniques enable whole-body imaging but lack the required spatial resolution. Conversely, near-infrared immunofluorescence (immuno-NIRF) is able to reveal tumor cells and/or other cell subsets in the TME by targeting the expression of a specific membrane receptor with fluorescently labeled monoclonal antibodies (mAb). Optical coherence tomography (OCT) provides three-dimensional morphological imaging of tissues without exogenous contrast agents. The combination of the two allows molecular and structural contrast at a resolution of ~15 µm, allowing for the specific location of a cell-type target with immuno-NIRF as well as revealing the three-dimensional architectural context with OCT. For the first time, combined immuno-NIRF and OCT of a tumor is demonstrated in situ in a xenograft mouse model of human colorectal cancer, targeted by a clinically-safe fluorescent mAb, revealing unprecedented details of the TME. A handheld scanner for ex vivo examination and an endoscope designed for imaging bronchioles in vivo are presented. This technique promises to complement nuclear imaging for diagnosing cancer invasiveness, precisely determining tumor margins, and studying the biodistribution of newly developed antibodies in high detail

Biomechanics of cells and tissues: What can we learn when we combine mechanical stimuli with microscopy?

Understanding the mechanical properties of biological tissues can shed light on how those tissues work and why, at times, they lose their functionality. Furthermore, a full characterization of a tissue’s viscoelastic behavior may provide relevant hints for tissue reparation and tissue engineering. To measure these properties in in-vitro or ex-vivo experiments, researchers often make use of indentation instruments, which looks at how a material deforms under the effect of a calibrated mechanical load. In the first part of my talk, I will show how this technique can be used to determine the mechanical properties of brain slices, and I will comment on which kind of information those measurements can provide. I will show, for instance, that different regions of the brain have remarkably different viscoelastic properties, which seem to be correlated with the cell density measured, in a parallel experiment, via fluorescent microscopy. As this example highlights, indentation measurements alone are often not sufficient to understand why certain tissues have certain mechanical properties. Under a (not transparent) surface, biological materials are often inhomogeneous and anisotropic. Because the indentation stress propagates several microns deep into the sample, without a proper imaging tool coupled to the indentation instrument, it is impossible to extract useful information on the mechanics of the material the sample is made of. As a point in case, I will show our latest measurements of the mechanical properties of chick embryos, where, combining indentation with optical coherence tomography (OCT), we could precisely map the stiffness of the spine from head to tail – a measurement that may provide interesting cues in the analysis of somites formation and growth. I will also show how the combination of indentation and OCT might find its way in scar and burn classification, introducing a new instrument for skin characterization that our group has just recently completed. Finally, I will show some preliminary results on the use of multiphoton imaging for tissue mechanics characterization. In this last part of the talk, I will show that it is indeed possible to look at the displacement and deformation of cells in a thin slice of tissue while the tissue is compressed by a calibrated mechanical stroke. This approach may pave the way for a much more thorough analysis of the origin of certain mechanical properties of tissues, where the contribution of the individual cells to the viscoelastic features of the materials can be finally disentangle from that of the extracellular matrix. This project was supported by LASERLABEUROPE under the EC’s Seventh Framework Program (Grant agreement No. 284464), by the European Union’s Seventh Framework Programme (FP/20072013)/ERC grant agreement no. 615170, by the Dutch Technology Foundation (STW) under the OMNE program (13183 and under the iMIT program (P11–13). Declaration of interest: Davide Iannuzzi is founder, shareholder, and advisor of Optics11

In vivo subdiffuse scanning laser oximetry of the human retina

Scanning laser ophthalmoscopes (SLOs) have the potential to perform high speed, high contrast, functional imaging of the human retina for diagnosis and follow-up of retinal diseases. Commercial SLOs typically use a monochromatic laser source or a superluminescent diode for imaging. Multispectral SLOs using an array of laser sources for spectral imaging have been demonstrated in research settings, with applications mainly aiming at retinal oxygenation measurements. Previous SLO-based oximetry techniques are predominantly based on wavelengths that depend on laser source availability. We describe an SLO system based on a supercontinuum (SC) source and a double-clad fiber using the single-mode core for illumination and the larger inner cladding for quasi-confocal detection to increase throughput and signal-to-noise ratio. A balanced detection scheme was implemented to suppress the relative intensity noise of the SC source. The SLO produced dual wavelength, high-quality images at 10  frames  /  s with a maximum 20 deg imaging field-of-view with any desired combination of wavelengths in the visible spectrum. We demonstrate SLO-based dual-wavelength oximetry in vessels down to 50  μm in diameter. Reproducibility was demonstrated by performing three different imaging sessions of the same volunteer, 8 min apart. Finally, by performing a wavelength sweep between 485 and 608 nm, we determined, for our SLO geometry, an approximately linear relationship between the effective path length of photons through the blood vessels and the vessel diameter.

Endoscopic polarization-sensitive optical coherence tomography in multiple lung diseases (Conference Presentation)

Polarization-sensitive optical coherence tomography (PS-OCT) has been used to extract polarization properties of four different diseased lungs ex vivo, including fibrotic sarcoidosis (FS), chronic obstructive pulmonary disease (COPD), fibrotic extrinsic allergic alveolitis (fibrotic EAA) and cystic fibrosis (CF). An increase in alveoli size has been observed in COPD lungs. Furthermore, an increase in birefringence signal was observed for FS and fibrotic EAA. In CF, a few areas with thick patches of birefringence occurred. The results show potential of in vivo assessment of lung fibrosis. Histology slides of all lungs were acquired, and will be used to further interpret the results

In vivo polarization-sensitive optical coherence tomography of human burn scars: birefringence quantification and correspondence with histologically determined collagen density

Obtaining adequate information on scar characteristics is important for monitoring their evolution and the effectiveness of clinical treatment. The aberrant type of collagen in scars may give rise to specific birefringent properties, which can be determined using polarization-sensitive optical coherence tomography (PS-OCT). The aim of this pilot study was to evaluate a method to quantify the birefringence of the scanned volume and correlate it with the collagen density as measured from histological slides. Five human burn scars were measured in vivo using a handheld probe and custom-made PS-OCT system. The local retardation caused by the tissue birefringence was extracted using the Jones formalism. To compare the samples, histograms of birefringence values of each volume were produced. After imaging, punch biopsies were harvested from the scar area of interest and sent in for histological evaluation using Herovici polychrome staining. Two-dimensional en face maps showed higher birefringence in scars compared to healthy skin. The Pearson's correlation coefficient for the collagen density as measured by histology versus the measured birefringence was calculated at r=0.80 (p=0.105). In conclusion, the custom-made PS-OCT system was capable of in vivo imaging and quantifying the birefringence of human burn scars, and a nonsignificant correlation between PS-OCT birefringence and histological collagen density was found