In brain studies, the function of the cerebrospinal fluid (CSF) awakes growing interest, particularly related to studies of the glymphatic system in the brain, which is connected with the complex system of lymphatic vessels responsible for cleaning the tissues. The CSF is a clear, colourless liquid including water (H2O) approximately with a concentration of 99 %. In addition, it contains electrolytes, amino acids, glucose, and other small molecules found in plasma. The CSF acts as a cushion behind the skull, providing basic mechanical as well as immunological protection to the brain. Disturbances of the CSF circulation have been linked to several brain related medical disorders, such as dementia.
Our goal is to develop an in vivo method for the non-invasive measurement of cerebral blood flow and CSF circulation by exploiting optical and capacitive sensing techniques simultaneously. We introduce a prototype of a wearable probe that is aimed to be used for long-term brain monitoring purposes, especially focusing on studies of the glymphatic system. In this method, changes in cerebral blood flow, particularly oxy- and deoxyhaemoglobin, are measured simultaneously and analysed with the response gathered by the capacitive sensor in order to distinct the dynamics of the CSF circulation behind the skull. Presented prototype probe is tested by measuring liquid flows inside phantoms mimicking the CSF circulation.
A high-speed optical coherence tomography (OCT) with 1-μm axial resolution was applied to assess the thickness of a cell-free layer (CFL) and a spatial distribution of red blood cells (RBC) next to the microchannel wall. The experiments were performed in vitro in a plain glass microchannel with a width of 2 mm and height of 0.2 mm. RBCs were suspended in phosphate buffered saline solution at the hematocrit level of 45%. Flow rates of 0.1 to 0.5 ml/h were used to compensate gravity induced CFL. The results indicate that OCT can be efficiently used for the quantification of CFL thickness and spatial distribution of RBCs in microcirculatory blood flow.
Two-color emission was observed in three-layer heterostructure organic light emitting transistors (OLETs). These devices consisted of a light-emitting layer made of tris(8-hydroxyquinolinato)aluminium (Alq3) doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), sandwiched between hole and electron transport layers made of α,ω-dihexyl-quaterthiophene (DH-4T) and α,ω-diperfluorohexyl-quaterthiophene (DFH-4T), respectively. Ambipolar transfer curves were recorded from the fabricated devices, and two-color emission (red and green) was observed during transfer curve acquisition. Red emission was observed to take place at bias conditions supporting hole transport, while green emission occurred when electron-based current was dominant. Moreover, red emission originated from the Alq3:DCM layer, which was verified by comparing the measured spectrum of OLETs to that of corresponding Alq3:DCM organic light-emitting diodes (OLEDs). To investigate the origin of green emission, OLETs were fabricated without an electron transport layer. No green emission was observed, while red emission remained unchanged. Moreover, single-layer transistors and diodes fabricated from DFH-4T expressed green color emission similar to that of three-layer heterostructure OLETs. Therefore, we suggest that green emission originates from the electron transport layer.
Organic solar cells and organic LEDs are typically made of conductive and semi-conductive thin films. The uniformity requirement for these films is exceptionally high. In the case of multi-layer structures, surface characterization based methods (e.g. profilometer, atomic force microscope, scanning electron microscope) encounter certain challenges when attempting to detect the defects inside the structure. One way to overcome this drawback is by using synchronized thermography (ST). In this work ST is used to study multi-layered thin film structures. Indium Tin Oxide (ITO) was used as an example of conductive thin film and poly(3,4-ethylenedioxy-thiopene):poly(styrene-sulfonate) (PEDOT:PSS) was used as an example of a hole transporting layer. Uniformity differences were generated in these layers and ST was used to detect them. The results show that ST is capable of localizing small defects in the stack using a single infrared (IR) image. It can often be deduced from the same image in which layer the defect is located. This shows that ST is capable of profiling the structures of multi-layer thin films.
Uniformity of conductive materials is an important property which is measured during manufacturing and in finished
products, especially in electronics applications such as organic solar cells. Differences in uniformity are often very small,
invisible or below the surface of the sample. Therefore, they are not always detectable even by high-resolution imaging
systems. Respectively, electrical conductivity measurements are limited to those mainly between the measuring probes.
Uniformity difference measurements are time-consuming in the case of a large area characterization. To bypass the
described limitations, a simple heating and IR-imaging based system was designed and demonstrated with conductive
materials. Samples with different defects were used to investigate the correlation of conductance and defect positioning.
By making punched holes in the samples, it was possible to demonstrate how the local resistances of thin films have
functions to each other and how this may be observed on an IR-figure. Thermographs of punched thin films confirm that
those areas where the holes prevented the current flow have lower heat emissions. Therefore, it can also be concluded
that, generally, the temperature is highest at the areas where current density is highest. When comparing the defects of
bent samples to these punctured ones, the correlations of resistance and breakage areas were comparable. The applied
system is capable of localizing small defects in large-area samples using a single IR-image. This is a significant
advantage from the manufacturing process measurement point of view.
Micro lens arrays (MLA) can be utilized in various applications of light sensitive devices such as digital cameras or objective free microscopes, and 3D imaging because of their good light collection efficiencies. Many of the fabrication methods used today require heat or expensive equipment or molds and that is why there is a need for a simple and cost effective fabrication method for MLAs. An inkjet printing based production method for low-cost micro lenses is presented here. By pre-patterning the used substrate the printing accuracy and the shape of the lenses is improved. The surface patterning is done with photolithography to fabricate round, shallow reservoirs for the lenses to be printed in. The liquid lens material is then inkjet printed into them. The pattern edges prevent the spreading of the ink outside the wanted area increasing the tolerance for printing inaccuracy and resulting to the uniform array of micro lenses. By depositing the ink to the reservoir, the ink forms a convex surface a.k.a. a lens. The used lens material is negative photoresist, so after printing it is cured with UV-light and baked in a hot plate to solidify the lens matrix. By placing different amount of ink in a reservoir the height of the lenses changes and thus the focus of the lens can be adjusted making the proposed method versatile tool for MLA fabrication.
We present the use of sub-micron resolution optical coherence tomography (SMR SD-OCT) in volumetric
characterization of ink- jet printed color filters, aimed for electronic paper display (EPD). The device used in the study is based on supercontinuum light source, Michelson interferometer centered at 600 nm and employs 400-800 nm spectral region. Spectra are acquired at a continuous rate of 140,000 per second. Color filter array of 143 μm x 141 μm sized and 6 rtm deep ink pools was studied. The volumetric OCT reconstruction was done using the experimental SMR SD-OCT device and a commercial SD-OCT imaging system. The ink layer in the pools was estimated to be 2μm thin. The optical profilometer was used for reference measurements.
We present the use of sub-micron resolution optical coherence tomography (OCT) in quality inspection for printed
electronics. The device used in the study is based on a supercontinuum light source, Michelson interferometer
and high-speed spectrometer. The spectrometer in the presented spectral-domain optical coherence tomography
setup (SD-OCT) is centered at 600 nm and covers a 400 nm wide spectral region ranging from 400 nm to 800
nm. Spectra were acquired at a continuous rate of 140,000 per second. The full width at half maximum of the
point spread function obtained from a Parylene C sample was 0:98 m. In addition to Parylene C layers, the
applicability of sub-micron SD-OCT in printed electronics was studied using PET and epoxy covered solar cell,
a printed RFID antenna and a screen-printed battery electrode. A commercial SD-OCT system was used for
reference measurements.
Fast method for identifying the internal limiting membrane (ILM) and retinal pigment epithelium (RPE) from optical
coherence tomography images is demonstrated. To avoid unnecessary increment of calculation time, a strong downsampling
of the original data set is performed to reduce a number of processed pixels. In ILM segmentation, the
obtained data cube is filtered with two different kinds of parameters and two estimates for the position of ILM is
determined. A simple smoothness value is determined for both estimates and better estimate is used for future
processing. A smaller portion of pixels around estimated ILM are extracted from the down sampled data and filtered
again and new estimation for ILM position is determined. That procedure is repeated with smaller portion of pixels
around ILM and with different filtering parameters. The principle of RPE segmentation is very much similar with ILM
identification. Only the used filtering and processing parameters are changed. Algorithm was tested with eight data sets
with good reliability. Over 97% of each scans had smaller segmentation error than 5 pixels. Total required data
processing time (ILM and RPE segmentation) for data volume with (600x1500x128) pixels was less than 9 seconds.
Simple and robust method for identifying the retinal pigment epithelium (RPE) from optical coherence tomography
images is demonstrated. At first, the maximum intensity value of each A-scans were determined and the
depth position of those pixels are identified. The obtained 2D matrix is used as first estimation for the position
of RPE. The erroneous pixel from the RPE is masked out and new approximation for them is calculated based
on the neighbouring pixels. Finally, the obtained RPE matrix is smoothened. The RPE identification is used for
separating the retina and choroid from optical coherence tomography images obtained by 830 nm spectral domain
OCT. Both normal and ARMD patient eye were investigated to demonstrate the usability of that method. The
calculation time for three dimensional data set (1024x450x137 pixels) was only 16 seconds and it identifies RPE
reliably.
Blood flow imaging of deep posterior eye has been demonstrated by using 1-μm spectral-domain optical coherence tomography. The high contrast imaging of deep posterior eye, such as the choroid and the sclera, enables blood flow imaging of choroidal vessels and short posterior ciliary arteries. Optical coherence angiography (OCA) images of outer part from the retinal pigment epithelium (RPE) reveal the vasculature of the choroid and the particular vasculature of short posterior ciliary arteries so-called the circle of Zinn-Haller. To the best of our knowledge, this is the first demonstration for flow imaging the circle of Zinn-Haller with optical coherence tomography.
KEYWORDS: Optical coherence tomography, Image segmentation, 3D image processing, Angiography, Optical discs, Signal attenuation, Time metrology, Macula, Numerical analysis, In vivo imaging
We present an automated numerical method of compensating for retinal shadows in the choroid. In this method, signal extinction caused by retinal vessels is estimated by subtracting median A-scans obtained from beneath the retinal vessels and A-scans from the surrounding area. Adding the obtained offset vector to A-scans from beneath the retinal vessels allows compensating for shadows in the choroid. In vivo imaging of the human eye was performed by 840-nm-band standard resolution spectral domain optical coherence tomography (SD-OCT), and choroidal vasculature projection images were calculated. Removal of retinal shadows distinctly improved the readability of choroidal images.
High-speed, high-resolution full-range 1 μm spectral-domain optical coherence tomography has been demonstrated. The axial resolution of 7 μm and the depth range of 2.6 mm in tissue are achieved with the line rate of 46,900 Hz. The sensitivity of 98 dB is obtained with full-range imaging. These parameters are comparable or superior than those of commercially available ophthalmic instruments. Three dimensional structures of the retina and the choroid are visualized with the high axial resolution. High penetration property of 1 μm wavelength band in the deeper region of the posterior human eye enable high-contrast imaging of the choroid. In addition to that, vessels outer the choroid are visualized.
Two different paper grades were tested with a clearing agent to measure how much mechanical smoothening can improve transparency inside paper. The paper grades were newsprint and supercalendered paper. The paper furnishes of both papers were alike, but the supercalendered paper was mechanically smoothened. Anise oil was used as the clearing agent, but similar measurements were also done with air and water. Black lines 8.5 μm to 281.1 μm wide were placed behind layers of cleared paper and transparency was measured with a microscope. When anise oil was the clearing agent, supercalendering improved transparent paper grammage from 139 g/m2 to 164 g/m2. With water the improvement was from 40 g/m2 to 51 g/m2. With air the improvement was not determinable. As a conclusion, it is recommended that paper is smoothened if it needs to be studied optically. Optical coherence tomography, for example, would benefit from this treatment.
Quantification of the three-dimensional (3D) retinal vessel structure and blood flow is demonstrated. 3D blood flow distribution is obtained by Doppler optical coherence angiography (D-OCA). Vessel parameters, i.e. diameter, orientation, and position, are determined in an en face vessel image. The Doppler angle is estimated as the angle between the retinal vessel and the incident probing beam in representative cross-sectional flow image which extracted from the 3D flow distribution according to the vessel parameters. Blood flow velocity and volume rate can be quantified with these vessel parameters. The retinal blood flow velocity and volume rate are measured in the retinal vessels around the optic nerve head.
Full-range spectral domain optical coherence tomography (SD-OCT) with a 1-μm band light source is demonstrated.
The phase of reference arm is modulated simultaneously as the probing beam laterally scans the sample
(B-scan). The obtained two dimensional spectral interferogram is processed by Fourier transform method to
obtain complex spectrum which leads to full-range OCT image. The measurement speed of this system was 7.96
kHz, the measured axial resolution was 9.6 μm in air and the sensitivity was 99.4 dB. To demonstrate the effect
of mirror image elimination, in vivo human eye pathology was measured.
A numerical method to compensate retinal shadows in choroid is presented. The averaged A-scans beneath retinal vessels and A-scans surrounded by them are calculated. The effect of absorption is estimated by subtracting those A-scans. By adding that offset value to A-scans beneath the retinal vessels, the shadows in the choroid are compensated. In vivo imaging of human eye was performed by 840 nm band standard resolution spectral domain optical coherence tomography and choroidal vasculature projection images were calculated. The removal of retinal shadows improves the readability of choroidal images.
This paper introduces a novel optical method to measure liquid penetration into porous, highly scattering media. Testing was conducted by measuring the sorption of glycerol into a paper sample consisting of cellulose fibre tissue with a grammage of 115 g m-2. During wetting, optical coherence tomography (OCT) was used to detect dynamical changes in the sample's scattering properties. Distinguishing the border between the dry and the wetted area on the basis of separate A-scans was a challenging task. However, wetting behaviour could be investigated in the depth direction simply by constructing a composite image of the separate scans. In addition, the method also allowed the imaging of swelling behaviour in paper.
Paper samples with a grammage between 50-200 g/m2 were compressed from 313 to 1105 kg/m3. During pressing, laser pulses were shot through them and delays in pulse propagation and light transmission in the compressed paper were observed with a streak-camera. The results show that the transmitted intensity depends mainly on the paper's grammage and is inversely proportional to it. Contrary to earlier TOF lidar measurements conducted during compression, delays in the propagation of photons decreased in paper samples with a grammage smaller than 280 g/m2. This result suggests that there is a grammage limitation at about 100 g/m2. When a streak-camera is used it allows the transmittance and propagation delay of photons to be obtained concurrently. As a result, changes in grammage and thickness can be evaluated separately. In addition, the paper presents a light transmittance and propagation delay dependent equation for porosity.
The refractive index of paper was determined by measuring the propagation delay of photons in optically cleared paper boards. The determination was based on the assumption that photon propagation delay achieves minimum value as the paper is optimally cleared. The measured paper sheets was made from elemental chlorine-free market pulp, i.e. fully bleached, unbeaten, softwood kraft pulp. Nine different clearing agents with a refraction index between 1.329 and 1.741 were eLuperimented with. According to the streakmem measurements, the refractive index of the test paper was 1.557.
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