Fig 1 - uploaded by Lothar Lilge
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A) Experimental setup illustrating the raster scan conducted to collect reflectance signal. The image shows the microfluidic channels (area C), which were filled, through reservoirs A & B. Optical fiber was raster scanned in a pattern depicted above. The y step size was kept constant at 5 μm and the x step size was varied while keeping a constant FOV. The illuminating fiber provides oblique collimated illumination (angle was kept close to 45º with the y axis pointing downwards) to the microfluidic phantom covered by scattering layers (D) of different thicknesses and optical properties The solid view presents a better representation of the layers, area C was completely covered with scattering layers D. The detector fiber then transfers the reflected photons to the spectrometer. B) Image of microfluidic platform taken with 10x objective at ≈ unit magnification. The FOV for the scanning experiments are outlined by the rectangle (1x0.060 mm 2 ). The area of microfluidic is 5.75x5 mm 2 .
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... Resolved Diffuse Reflectance Imaging System is described in Fig. 1. Wide-field, oblique collimated illu- mination of the entire sample was achieved with a 0.40 mm core optical fiber (Silica fibers, NA 0.22, Thorlabs Inc., USA) coupled to a broadband white light source, HPLS-30-02 (Thorlabs Inc, USA) and a fiber optic collimator (OZ Optics, Canada). For image acquisition, a region of interest (FOV) of ...
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... microfluidic platform is composed of narrow channels covered with various scattering layers (prepared separately) placed atop (D in Fig 1). The microchannel plate was manufactured from a clear polydimethylsiloxane (PDMS, silicone) material, n=1.56 in the visible spectrum without scattering particles. ...
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... parallel grooves were designed to approximate a nailfold microvascular spatial pattern with mean physical dimensions as: 34μm wide groove, separated by 82μm spacing, and the groove's height -30μm 2,21 . The solution of the 90-95% oxygenated, human haemoglobin (Agat-Med, Russia, 160 g/l) was injected in the reservoir A in Fig 1 (2mm x 2mm) by means of 18 Gauge needle syringe 22 . Hemoglobin was then redistributed from the reservoir A to reservoir B (2mm x 2mm) to obtain a close to uniform distribution of hemoglobin in the microfluidic channels (area C in Fig 1). ...
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... solution of the 90-95% oxygenated, human haemoglobin (Agat-Med, Russia, 160 g/l) was injected in the reservoir A in Fig 1 (2mm x 2mm) by means of 18 Gauge needle syringe 22 . Hemoglobin was then redistributed from the reservoir A to reservoir B (2mm x 2mm) to obtain a close to uniform distribution of hemoglobin in the microfluidic channels (area C in Fig 1). ...
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... used to compute the optical properties of the samples 26 . Spectral data acquired at each point resulted in a dataset of the dimensions {x, y, wavelengths} ={500 μm/x step size, 50 μm/y step size, 3648 wavelengths}. The raster scan was performed for x and y step sizes of 2, 5, 10, 20 and 50μm, for two FOVs 500 x 50μm and 1000 x 60μm as shown in Fig. 1. The spectral dimension was reduced to a single point by averaging a wavelength band centered at 545nm with a bandwidth of 100nm, which provides good contrast for haemoglobin and can be easily emulated by green channel of a standard RGB chip according to the Green band of the Bayer filter ...
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... alternating dark and light bands represent an absorption contrast within narrow FOVs after the light has traveled through the hemoglobin grooves of the phantom under a scattering layer (Fig. 1B). In Table 1, proper- ties of the layers are listed for a selected wavelength, λ=545 nm. For labeling purposes, scattering properties were coded with letters A to E, thickness of the layers was coded from 1 to 5. Altogether 5 thickness and 5 scattering lay-ers were used in experimental testing, giving 25 datasets for image analysis. ...
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... Further applications are illustrated in imaging slices of rat retina. To show how cellular imaging can be achieved through deep scattering layers we describe how we successfully imaged a 50µm diameter microchannel filled with hemoglobin covered by an intralipid layer that matched the scattering properties (µs' ) of the epithelium [22]- [24], at thicknesses ranging up to 360 µm in a Polydimethylsiloxane (PDMS) matrix. The image was collected by scanning the area of interest in both the transmission and reflected modes. ...
... To create the diffusive medium layers, a solution of intralipid (I141, Sigma-Aldrich Inc, USA) was diluted in deionized water to obtain 1% and 2%. This concentration was selected to have a scattering coefficient μs' of 1.3 [mm -1 ] at λ=545nm that matches the scattering properties of the epithelium [22]- [24]. The layers tested had thicknesses of 240, 320 and 360 µm. ...
We describe an imaging approach based on an optical setup made up of a miniature, lensless, minimally invasive endoscope scanning a sample and matching post processing techniques that enables enhanced imaging capabilities. The main scopes of this article are that this approach enables imaging beyond highly scattering medium and increases the resolution and signal to noise levels reaching single cell imaging. Our approach has more advantages over ordinary endoscope setups and other imaging techniques. It is not mechanically limited by a lens, the fiber can acquire images over long time periods (unlike current imaging methods such as OCT etc.), and the imaging can be obtained at a certain working distance above the surface, without interference to the imaged object. Fast overlapping scans enlarge the region of interest, enhance signal to noise levels and can also accommodate post-processing super-resolution algorithms. Here we present that due to the setup properties, the overlapping scans also lead to dramatic enhancement of non-scattered signal to scattered noise. This enables imaging through highly scattering medium. We discuss results obtained from in-vitro investigation of weak signals of ARPE cells, rat retina, and scattered signals from Polydimethylsiloxane (PDMS) micro channels filled with hemoglobin and covered by intralipids mimicking consequently blood capillaries and the epidermis of human skin.The development of minimally invasive procedures and methodologies for imaging through scattering medium such as tissues can vastly enhance biomedical diagnostic capabilities for imaging internal organs. We thereby propose that our method may be used for such tasks in vivo.
