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Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor 01 December 2022 {: .label .label-blue } New journal paper published in Materials! Authors Adrian Cioabla,Virgil-Florin Duma,Corina Mnerie,Ralph-Alexandru Erdelyi, George Mihai Dobre, Adrian Bradu, and Adrian Podoleanu Title and coordinates “[Enhanced resolution optoacoustic microscopy using a Effect of an Anaerobic Fermentation Process on 3D-Printed PLA Materials of a Biogas-Generating Reactor, Materials 15, 8571 (2022). Abstract 3D-printed materials are present in numerous applications, from medicine to engineering. The aim of this study is to assess their suitability for an application of interest today, that of testing of 3D-printed polylactic acid (PLA)-based reactors for biogas production using anaerobic digestion. The impact of temperature, pH, and aqueous phase on the tested bioreactor is investigated, together with the effect of the gaseous phase (i.e., produced biogas). Two batches of materials used separately, one after another inside the bioreactor were considered, in a realistic situation. Two essential parameters inside the reactor (i.e., pH and temperature) were continuously monitored during a time interval of 25 to 30 days for each of the two biogas-generating processes. To understand the impact of these processes on the walls of the bioreactor, samples of 3D-printed material were placed at three levels: at the top (i.e., outside the substrate), in the middle, and at the bottom of the bioreactor. The samples were analyzed using a non-destructive imaging method, Optical Coherence Tomography (OCT). An in-house developed swept-source (SS) OCT system, master–slave (MS) enhanced, operating at a central wavelength of 1310 nm was utilized. The 3D OCT images related to the degradation level of the material of the PLA samples were validated using Scanning Electron Microscopy (SEM). The differences between the impact of the substrate on samples situated at the three considered levels inside the reactor were determined and analyzed using their OCT B-scans (optical cross-section images). Thus, the impact of the biogas-generating process on the interior of the bioreactor was demonstrated and quantified, as well as the capability of OCT to perform such assessments. Therefore, future work may target OCT for in situ investigations of such bioreactors.

En-face OCT/fluorescence endomicroscopy for minimally invasive imaging using a robotic scanner Authors Manuel J. Marques, Michael R. Hughes, Khushi Vyas, Andrew Thrapp, Haojie Zhang, Adrian Bradu, Grigory Gelikonov, Petros Giataganas, Christopher J. Payne, Guang-Zhong Yang, and Adrian Podoleanu Title and coordinates En-face optical coherence tomography/fluorescence endomicroscopy for minimally invasive imaging using a robotic scanner, J. of Biomedical Optics 24(6), 066006 (2019). Abstract We report a compact rigid instrument capable of delivering en-face optical coherence tomography (OCT) images alongside (epi)-fluorescence endomicroscopy (FEM) images by means of a robotic scanning device. Two working imaging channels are included: one for a one-dimensional scanning, forward-viewing OCT probe and another for a fiber bundle used for the FEM system. The robotic scanning system provides the second axis of scanning for the OCT channel while allowing the field of view (FoV) of the FEM channel to be increased by mosaicking. The OCT channel has resolutions of 25 / 60 μm (axial/lateral) and can provide en-face images with a FoV of 1.6 × 2.7 mm^2. The FEM channel has a lateral resolution of better than 8 μm and can generate a FoV of 0.53 × 3.25 mm^2 through mosaicking. The reproducibility of the scanning was determined using phantoms to be better than the lateral resolution of the OCT channel. Combined OCT and FEM imaging were validated with ex-vivo bovine and porcine tissues, with the instrument mounted on an arm to ensure constant contact of the probe with the tissue. The OCT imaging system alone was validated for in-vivo human dermal imaging with the handheld instrument. In both cases, the instrument was capable of resolving fine features such as the sweat glands in human dermal tissue and the alveoli in porcine lung tissue.

Enhanced resolution optoacoustic microscopy using a picosecond high repetition rate Q-switched microchip laser 29 November 2022 {: .label .label-blue } New journal paper published in Journal of Biomedical Optics! Authors Gianni Nteroli, Giulia Messa, Manoj K. Dasa, Antti Penttinen, Antti Härkönen, Mircea Guina, Adrian Podoleanu, Stella Koutsikou, and Adrian Bradu Title and coordinates “Enhanced resolution optoacoustic microscopy using a picosecond high repetition rate Q-switched microchip laser,” Journal of Biomedical Optics 27(11), 110501 (2022). ...

Fast spectrally encoded Mueller optical scanning microscopy Authors Sylvain Rivet, Matthieu Dubreuil, Adrian Bradu, and Yann Le Grand Title and Coordinates Fast spectrally encoded Mueller optical scanning microscopy, Scientific Reports 9, 3972 (2019). Abstract Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometre scale. However, the development of Mueller microscopes poses an instrumental challenge: the production of polarimetric parameters must be sufficiently quick to ensure fast imaging, so that the evolution of these parameters can be visualised in real-time, allowing the operator to adjust the microscope while constantly monitoring them. In this report, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum, collected every 10 $\mu$s for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous display of all the polarimetric parameters, at the unequalled rate of 1.5 Hz (for an image of 256 $\times$ 256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens.

Gabor fusion Master Slave Optical Coherence Tomography Authors Ramona Cernat, Adrian Bradu, Niels Møller Israelsen, Ole Bang, Sylvain Rivet, Pearse A. Keane, David-Garway Heath, Ranjan Rajendram, and Adrian Podoleanu Coordinates Gabor fusion master slave optical coherence tomography, Biomed. Opt. Express 8, 813-827 (2017). Abstract This paper describes the application of the Gabor filtering protocol to a Master/Slave (MS) swept source optical coherence tomography (SS)-OCT system at 1300 nm. The MS-OCT system delivers information from selected depths, a property that allows operation similar to that of a time domain OCT system, where dynamic focusing is possible. The Gabor filtering processing following collection of multiple data from different focus positions is different from that utilized by a conventional swept source OCT system using a Fast Fourier transform (FFT) to produce an A-scan. Instead of selecting the bright parts of A-scans for each focus position, to be placed in a final B-scan image (or in a final volume), and discarding the rest, the MS principle can be employed to advantageously deliver signal from the depths within each focus range only. The MS procedure is illustrated on creating volumes of data of constant transversal resolution from a cucumber and from an insect by repeating data acquisition for 4 different focus positions. In addition, advantage is taken from the tolerance to dispersion of the MS principle that allows automatic compensation for dispersion created by layers above the object of interest. ...

Group refractive index and group velocity dispersion measurement by complex master slave interferometry Authors Sylvain Rivet, Adrian Bradu, Fiona Bairstow, Hisham Forrière, and Adrian Podoleanu Coordinates Group refractive index and group velocity dispersion measurement by complex master slave interferometry, Opt. Express 26, 21831-21842 (2018). Abstract This paper demonstrates that the complex master slave interferometry (CMSI) method used in spectral domain interferometry (SDI) can efficiently be used for accurate refractive index and group velocity dispersion measurements of optically transparent samples. For the first time, we demonstrate the relevance of the phase information delivered by CMSI for dispersion evaluations with no need to linearize data. The technique proposed here has been used to accurately measure the group refractive index and the group velocity dispersion of a strong dispersive sample (SF6 glass), and a weak dispersive one (distilled water). The robustness of the technique is demonstrated through the manipulation of several sets of experimental data.

{: w=“700” h=“400” .shadow} I had an invited talk at the 1st International Conference Advances in 3OM: Opto-Mechatronics, Opto-Mechanics and Optical Metrology {: .text-center .fs-6} on Combining Photoacoustic and Optical Coherence Tomography Imaging for non-destructive applications. Soon, an SPIE Proceedings on combining these two technologies are going to be published. A link will be posted here. Thanks the organisers for inviting me! Link for proceedings: {: .label .label-yellow } Gianni Nteroli, Adrian Podoleanu, and Adrian Bradu, “Combining photoacoustic and optical coherence tomography imaging for nondestructive testing applications,” Proc. SPIE, 12170, Advances in 3OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology; 121700P (2022). ...

Methods for dental shade determination New Proceedings Published! Authors Christa Serban, Gianni Nteroli, Emanuela L. Craciunescu, Meda L. Negrutiu, Helmine Serban, Virgil F. Duma, Adrian Bradu, Adrian Podoleanu, Cosmin Sinescu Coordinates Methods for dental shade determination Proceedings Volume 11942, Lasers in Dentistry XXVIII; 1194206 (2022) Event: SPIE BiOS, 2022, San Francisco, California, United States Goal The aim of this in-vitro study was to evaluate comparatively the capability of software-based color analysis of mobile phone photography, with the spectrophotometric and visual methods for dental shade determination. ...

Multispectral photoacoustic microscopy and optical coherence tomography using a single supercontinuum source Authors Magalie Bondu, Manuel J. Marques, P.M. Moselund, G. Lall, Adrian Bradu, and Adrian Podoleanu Coordinates Multispectral photoacoustic microscopy and optical coherence tomography using a single supercontinuum source, Photoacoustics 9, 21-30 (2018). Abstract In this paper we report on the use of a single supercontinuum (SC) source for multimodal imaging. The 2-octave bandwidth (475-2300 nm) makes the SC source suitable for optical coherence tomography (OCT) as well as for multispectral photoacoustic microscopy (MPAM). The IR band centered at 1310 nm is chosen for OCT to penetrate deeper into tissue with 8 mW average power on the sample. The 500-840 nm band is used for MPAM. The source has the ability to select the central wavelength as well as the spectral bandwidth. An energy of more than 35 nJ within a less than 50 nm bandwidth is achieved on the sample for wavelengths longer than 500 nm. In the present paper, we demonstrate the capabilities of such a multimodality imaging instrument based on a single optical source. In-vitro mouse ear B-scan images are presented.

Optical Coherence Tomography Investigations and Modeling of the Sintering of Ceramic Crowns Authors Virgil Florin Duma, Cosmin Sinescu, Adrian Bradu and Adrian Podoleanu, Coordinates Optical Coherence Tomography Investigations and Modeling of the Sintering of Ceramic Crowns, Materials 12, 947 (2019). Abstract Dental prostheses are sintered in ovens that sometimes suffer from a loss of calibration. This can lead to variations of the sintering temperature outside the range recommended by the manufacturer. Stress and even fractures in dental ceramics may occur, and this leads to the necessity to rebuild the dental construct. The aim of this work is to monitor the quality of sintering processes using an established biomedical imaging technique—optical coherence tomography (OCT). ...