Tapio Fabritius

Full-range, high-speed, high-resolution 1-μm spectral-domain optical coherence tomography using BM-scan for volumetric imaging of the human posterior eye

An alternative optical coherence tomography (OCT) to clinical ophthalmic 830 nm spectral-domain OCTs (SD-OCT) is demonstrated. An axial resolution of 7.4 microm, ranging depth of 4.2 mm in tissue, sensitivity of 98.5 dB, and detection speed of 38,300 axial scans/s have been achieved. These are comparable or superior to those of recently commercially available ophthalmic 830 nm SD-OCTs in clinics. In addition, fast volumetric imaging for the in vivo human posterior eye with high-contrast of the choroid is achieved. A broadband 1.04 microm light source enables the high-contrast and high resolution imaging of the retina and choroid. The ranging depth is extended by applying a full-range imaging method with an electro-optic modulator (BM-scan method). A prototype high-speed InGaAs line scan camera with 1024 pixels is used. A newly reported sensitivity improvement property of the BM-scan method demonstrates a sensitivity enhancement of 5.1 dB. We also introduce a newly developed resampling calibration method of spectrum that is independent of the intrinsic dispersion mismatch of the interferometer. The three-dimensional structure of the in vivo human optic nerve head with a very deep cupping is successfully visualized.

Quantitative retinal-blood flow measurement with three-dimensional vessel geometry determination using ultrahigh-resolution Doppler optical coherence angiography

Retinal blood flow quantification by retinal vessel segmentation with Doppler optical coherence angiography is presented. Vessel diameter, orientation, and position are determined in an en face vessel image and two representative cross-sectional flow images of the vessel. Absolute blood flow velocity is calculated with the help of the measured Doppler frequency shift and determined vessel angle. The volumetric flow rate is obtained with the position and the region of the vessel lumen. The volumetric blood flow rate of retinal arteries before and after a bifurcation is verified in a healthy human eye.

Automated segmentation of the macula by optical coherence tomography

This paper presents optical coherence tomography (OCT) signal intensity variation based segmentation algorithms for retinal layer identification. Its main ambition is to reduce the calculation time required by layer identification algorithms. Two algorithms, one for the identification of the internal limiting membrane (ILM) and the other for retinal pigment epithelium (RPE) identification are implemented to evaluate structural features of the retina. Using a 830 nm spectral domain OCT device, this paper demonstrates a segmentation method for the study of healthy and diseased eyes.

Refractive index matching improves optical object detection in paper

The demand for high-quality recycled pulp products has increased the need for an efficient deinking process. Assessing process efficiency via residual ink on test sheets has so far been limited to the sheet surface due to the poor transparency of paper. A refractive index matching method was studied to obtain a quantitative measure of particles within the volume of a paper sheet. In actual measurements a glass plate with etched lines from 8.5 ?m to 281.1 ?m wide was placed beneath the layers of cleared paper, and visible lines were counted with a microscope. Three different paper grades were tested with transparentizing agents. A diffusion theory-based regression model was used to find a correlation between transparency, paper grammage and paper thickness. These equations enable the determination of the size of an object detectable from a paper with a certain transparentizing agent or the parameters of a test sheet needed to detect objects of a known size. Anise oil was found to be the better of the two agents used, and they both had better transparentizing ability than air or water. The transparent paper grammage of the paper grades was determined for all the tested media. Papers transparency was found to depend more on papers thickness than grammage.

Automated retinal shadow compensation of optical coherence tomography images

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.

All Silk-Screen Printed Polymer-Based Remotely Readable Temperature Sensor

In this paper, we present the fabrication and characterization results of a remotely readable flexible temperature sensor. The sensor has been fabricated with screen printing technology and it consists of a polymer-based capacitor (ASAHI CR18-KTI polymer paste) as a temperature sensitive component added to the antenna coil (ASAHI LS411-AW silver paste) for remote reading purposes. The resonance frequency of the sensor (i.e., the formed LC network) is measured as a function of temperature. The sensor has been characterized in the temperature range of 0 °C-70 °C and the total sensitivity over this range is ~9 kHz/°C. The sensors normalized temperature response is independent from the polymer capacitors thickness and the effective capacitor area, which enables reasonable performance despite fabrication process induced inaccuracies. Due to the inexact nature of the resonance peak measurement, a dataanalysis algorithm was developed to enhance the accuracy of the measurement method. In addition, the sensor response to the misaligned reader and the sensor self-heating effect, due to the inductive excitation voltage, are considered. Finally, the calibration of such a sensor is discussed.

Reliability Study on Adhesive Interconnections in Flex-to-Flex Printed Electronics Applications Under Environmental Stresses

The reliability of conductive adhesive interconnections in flex-to-flex printed electronics applications under thermal cycling and cyclic bending tests is investigated in this paper. The components under study consisted of a backplane, having screen-printed silver wiring on polyethylene terephthalate film, fabricated in a roll-to-roll process, and a flexible functional component mimic stacked on top of the backplane. Each test component contained four daisy-chained conductive adhesive interconnections, and their reliability was monitored in situ with a four-point dc resistance measurement during tests. In addition, the effect of supportive nonconductive adhesives on structure reliability was studied in various configurations. The accelerated life test results proved that the long-term reliability of the studied components can be enhanced by adding supportive adhesive between the flexible layers. In both thermal cycling and cyclic bending tests, the most reliable method was found to be the configuration with supportive adhesive around the top layer sides, attaching the two layers totally together, whereas the configuration with no supportive adhesive at all showed the worst reliability. The failure analysis emphasized that the critical factor, in terms of reliability, was silver conductor delamination from the backplane surface at the interconnection area.

Electrical heating synchronized with IR imaging to determine thin film defects

Measuring conductive thin film properties during production and in end products is a challenge. The main demands for the measurements are: production control, reliability and functionality in final applications. There are several ways to measure thin film quality in a laboratory environment, however these methods are poorly applicable for production facilities. In order to bypass the limitations of existing methods, a simple synchronized heating and IR-imaging based system was implemented. To demonstrate the proposed method, Indium Tin Oxide (ITO) was selected as an example of conductive thin films. PET-ITO films were bent to obtain samples with defects. The proposed method was used and automated signal processing was developed. The results show that the system developed here is suitable for defining breakage types and localizing defects.

Characterization of ink-jet printed RGB color filters with spectral domain optical coherence tomography

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.

Blood flow imaging at deep posterior human eye using 1 μm spectral-domain optical coherence tomography

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.