1,721,547 research outputs found
Phase sensitive optical coherence microscopy for photothermal imaging of gold nanorods
Full text linkWe describe a swept source based phase sensitive optical coherence microscopy (OCM) system for photothermal imaging of gold nanorods (GNR). The phase sensitive OCM system employed in the study has a displacement sensitivity of 0.17 nm to vibrations at single frequencies below 250 Hz. We demonstrate the generation of phase maps and confocal phase images. By displaying the difference between successive confocal phase images, we perform the confocal photothermal imaging of accumulated GNRs behind a glass coverslip and behind the scattering media separately. Compared with two-photon luminescence (TPL) detection techniques reported in literature, the technique in this study has the advantage of a simplified experimental setup and provides a more efficient method for imaging the aggregation of GNR. However, the repeatability performance of this technique suffers due to jitter noise from the swept laser source
Towards an ultra-thin medical endoscope: multimode fibre as a wide-field image transferring medium
Full text linkMultimode optical fibres are attractive for biomedical and industrial applications such as endoscopes because of the small cross section and imaging resolution they can provide in comparison to widely-used fibre bundles. However, the image is randomly scrambled by propagation through a multimode fibre. Even though the scrambling is unpredictable, it is deterministic, and therefore the scrambling can be reversed. To unscramble the image, we treat the multimode fibre as a linear, disordered scattering medium. To calibrate, we scan a focused beam of coherent light over thousands of different beam positions at the distal end and record complex fields at the proximal end of the fibre. This way, the inputoutput response of the system is determined, which then allows computational reconstruction of reflection-mode images. However, there remains the problem of illuminating the tissue via the fibre while avoiding back reflections from the proximal face. To avoid this drawback, we provide here the first preliminary confirmation that an image can be transferred through a 2x2 fibre coupler, with the sample at its distal port interrogated in reflection. Light is injected into one port for illumination and then collected from a second port for imaging
Use of a supercontinuum white light in evaluating the spectral sensitivity of the pupil light reflex
Full text linkWe assessed the spectral sensitivity of the pupillary light reflex in mice using a high power super continuum white light (SCWL) source in a dual wavelength configuration. This novel approach was compared to data collected from a more traditional setup using a Xenon arc lamp fitted with monochromatic interference filters. Irradiance response curves were constructed using both systems, with the added benefit of a two-wavelength, equivocal power, output using the SCWL. The variables applied to the light source were intensity, wavelength and stimulus duration through which the physiological output measured was the minimum pupil size attained under such conditions. We show that by implementing the SCWL as our novel stimulus we were able to dramatically increase the physiological usefulness of our pupillometry system
Denoising Based on Noise Parameter Estimation in Speckled OCT Images Using Neural Network
No full textThis paper presents a neural network based technique to denoise speckled images in optical coherence tomography (OCT). Speckle noise is modeled as Rayleigh distribution, and the neural network estimates the noise parameter, sigma. Twenty features from each image are used as input for training the neural network, and the sigma value is the single output of the network. The certainty of the trained network was more than 91 percent. The promising image results were assessed with three No-Reference metrics, with the Signal-to-Noise ratio of the denoised image being considerably increased
Complementarity of OCT and radiography for imaging investigations in dentistry
Full text linkThere are numerous dental conditions that can appear in the human mouth, from bone diseases like periodontitis or bone loss produced by a massive infection, to common issues like dental cavities. We explored the possible range of dental (and associated bone) conditions using Optical Coherence Tomography (OCT) versus the gold standard of radiological investigations [Erdelyi R.A., Duma V.-F., et al, Materials 13, 4825, 2020]. Clinical and imaging investigations have been performed on real-life patients. Advantages and limitations of using these two imaging techniques were deduced, based on the fact that OCT has better resolution than radiographs (2 to 10 μm versus 75 to 150 μm, respectively), while radiography can perform a complete image of the entire mouth, in contrast to OCT, which has a limited penetration, of only 1 to 2 mm in tooth or soft tissue. The analyses of a range of dental conditions with both techniques clarified when it is better to choose a specific method: (i) for bone diseases, radiographs are more appropriate because they provide images of the entire mouth in one exposure and 3D images of dental conditions; (ii) OCT can spot small cavities in early stages, while radiographs cannot; (iii) measurements performed on cavities spotted with both imaging techniques proved that OCT can provide accurate dimensions, with high contrast and contrast-to-noise ratio. Thus, a classification of each of the two types of imaging techniques for each possible dental condition was obtained. A complementarity of OCT and radiography for investigations in dentistry was concluded
Phase estimation for global defocus correction in optical coherence tomography
Full text linkIn this work we investigate three techniques for estimation of the non-linear phase present due to defocus in opticalcoherence tomography, and apply them with the angular spectrum method. The techniques are: Least squarestting the of unwrapped phase of the angular spectrum, iterative optimization, and sub-aperture correlations. The estimated phase of a single en-face image is used to extrapolate the non-linear phase at all depths, whichin the end can be used to correct the entire 3-D tomogram, and any other tomogram from the same system
Superpixel guided active contour segmentation of retinal layers in OCT volumes
Full text linkRetinal OCT image segmentation is a precursor to subsequent medical diagnosis by a clinician or machine learning algorithm. In the last decade, many algorithms have been proposed to detect retinal layer boundaries and simplify the image representation. Inspired by the recent success of superpixel methods for pre-processing natural images, we present a novel framework for segmentation of retinal layers in OCT volume data. In our framework, the region of interest (e.g. the fovea) is located using an adaptive-curve method. The cell layer boundaries are then robustly detected firstly using 1D superpixels, applied to A-scans, and then fitting active contours in B-scan images. Thereafter the 3D cell layer surfaces are efficiently segmented from the volume data. The framework was tested on healthy eye data and we show that it is capable of segmenting up to 12 layers. The experimental results imply the effectiveness of proposed method and indicate its robustness to low image resolution and intrinsic speckle noise
New ways of combating demineralization: link between classic and allopathic medicine
Full text linkPrevention and allopathic medicine gained attention, since it is possible for dentists to prevent demineralization, using plants and natural substances with well-known efficacy. The purpose of this study was to present new methods for teeth remineralization. It was made a selection of 10 extracted teeth, maintained in physiological serum, with no color fading, decay or demineralization. It was induced demineralization, with ortho-phosphoric acid (concentration 45 %), for one minute. The probes were visually and with optical coherence tomography (OCT) inspected. The natural product and the bonding with additional nanoparticles of argent were created and applied on the demineralization zone of the both groups of teeth. Each tooth in the first group had one plain surface demineralized. The second group of teeth had a cavity prepared on one of each tooth’s side. The pastes were applied on the demineralized surfaces and in the demineralized cavities for two minutes. After time expired, the pasta applied on the first group of teeth was washed away; the bonding above the second group of teeth was light cured. The probes were again visually and with OCT inspected. It was observed an improvement in remineralizing the white marks on plain surfaces and in the created cavities, the OCT being able to detect different levels of remineralization. The efficacy of natural pasta depends on the time it is applied and the concentration of the different main substances. Also, the type of surface, plain or occlusal facets, may influence the substances’ penetration ability. The non-invasive specific feature of these products, low costs and safety are strong positive aspects of this method of remineralization. However, the natural process of remineralization is a long-lasting one; perfecting the main substances in order to accelerate the process, in addition to several in vivo studies would be necessary to be fulfilled
En-face optical coherence tomography revival
No full textQuite recently, we introduced a novel Optical Coherence Tomography (OCT) method, termed as Master Slave OCT (MS-OCT), especially to deliver en-face images. MS-OCT operates like a time domain OCT, selecting signal from a selected depth only while scanning the laser beam across the sample. Time domain OCT allows real time production of an en-face image, although relatively slowly. As a major advance, the Master Slave method allows collection of signals from any number of depths, as required by the user. MS-OCT is an OCT method that does not require resampling of data and can be used to deliver en-face images from several depths simultaneously. However, as the MS-OCT method requires important computational resources, the number of multiple depth en-face images produced in real-time is limited. Here, we demonstrate that taking advantage of the parallel processing feature of the MS-OCT technology by harnessing the capabilities of graphics processing units (GPU)s, information from 384 depth positions is acquired in one raster with real time display of 40 en-face OCT images. These exhibit comparable resolution and sensitivity to the images produced using the traditional Fourier domain based method. The GPU facilitates versatile real time selection of parameters, such as the depth positions of the 40 images out of a set of 384 depth locations, as well as their axial resolution. Here, we present in parallel with the 40 en-face OCT images of a human tooth, a confocal microscopy lookalike image, together with two B-scan OCT images along rectangular directions. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Resolution dependence on phase extraction by the Hilbert transform in phase calibrated and dispersion compensated ultrahigh resolution spectrometer-based OCT
Full text linkUltrahigh resolution optical coherence tomography (UHR-OCT) is enabled by using a broad band source. Simultaneously, this makes the OCT image more sensitive to dispersion mismatch in the interferometer. In spectral domain OCT, dispersion left uncompensated in the interferometer and detector non-linearities lead together to an unknown chirp of the detected interferogram. One method to compensate for the chirp is to perform a pixel-wavenumber calibration versus phase that requires numerical extraction of the phase. Typically a Hilbert transform algorithm is employed to extract the optical phase versus wavenumber for calibration and dispersion compensation. In this work we demonstrate UHR-OCT at 1300 nm using a Super continuum source and highlight the resolution constraints in using the Hilbert transform algorithm when extracting the optical phase for calibration and dispersion compensation. We demonstrate that the constraints cannot be explained purely by the numerical errors in the data processing module utilizing the Hilbert transform but must be dictated by broadening mechanisms originating from the experimentally obtained interferograms
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