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Roughness (Measured by Profilometry: Mechanical, Optical, and Laser)
Published in Enzo Berardesca, Peter Elsner, Klaus-P. Wilhelm, Howard I. Maibach, Bioengineering of the Skin: Methods and Instrumentation, 2020
Increasingly, special forms of the Michelson interferometer are in practical use, including a phase detector and a microscope based on interference. These instruments are suitable for high precision measurements.9 Although the vertical resolution is not quoted, it is presumably on the scale of 10 nm, based on a vertical range of about 100 μm. However, this range is not sufficient for studying surfaces rougher than those of the skin.
Measurement Techniques
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
Marvin C. Ziskin, Peter A. Lewin
Optical measuring techniques in the field of ultrasonics have an ancestry dating well back into the 19th century. Although a variety of optical measuring techniques is known from the literature, only a few of them can be applied in absolute determinations of sound field parameters in liquids. Investigations into the use of the liquid-surface technique as a means of visualization of field distribution were first carried out in 1951 by Schuster and for sound intensity measurements by Negishi in 1972 with a shadow-optical arrangement. Laser interferometers are used in almost all fields of measuring technique. Depending on the extent of the displacement, the interferometric measuring method must be adapted to the particular measuring problem. For the purpose of ultrasound measuring techniques, this means that only a few approaches, restricted in terms of sound pressure amplitude, sound field geometry, frequency, and pressure waveform, can be applied.
Medical Imaging Informatics
Published in Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam, Introduction to Computational Health Informatics, 2019
Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam
Optical coherence tomography (OCT) is an optical imaging modality, based on low-coherence interferometry. Like ultrasound imaging, OCT is based on signal reflections. The light is split by using two arms. The sample arm contains the item of interest and a reference arm, typically a mirror, providing the reference signal for the interference. The reflected light from the sample and the reference light combines to produce an interference pattern, if both lights traveled the “same” distance (difference between two distances is less than the coherence length). Light outside the short coherence length does not produce an interference pattern. The mirror in the reference arm is scanned to produce a reflectivity profile of the sample. OCT can capture fine-resolution (μm) images from biological tissues, employing near-infrared light. Near-infrared wavelengths allow deeper penetration into the optical scattering media. However, it is limited to imaging the top one to two mm of biological tissues; at larger depths, not enough light is reflected from the sample to be detected.
Axial length measurement failure rates using optical biometry based on swept-source OCT in cataractous eyes
Published in Expert Review of Medical Devices, 2022
Pedro Tañá-Rivero, Santiago Tañá-Sanz, Francisco Pastor-Pascual, Ramón Ruiz-Mesa, Robert Montés-Micó
Different optical biometers currently on the market are based on different technologies, which include partial coherence interferometry, optical low coherence reflectometry, optical low coherence interferometry, and swept-source optical coherence tomography. In this review we have analyzed several clinical articles reporting data on these cases using different optical biometers based on swept-source optical coherence tomography available in the market. As a general remark, we consider that optical biometers based on swept-source optical coherence tomography lead to only small failure rates when measuring axial length. From the analysis of the articles, we have to point out that in the few cases where the measurement was not possible, the cataract type of the eyes was mainly mature white or grade ≥ IV. The results reported in these articles revealed that optical biometers based on swept-source optical coherence tomography show good outcomes when measuring axial length in eyes with advanced cataracts.
Contact force sensors in minimally invasive catheters: current and future applications
Published in Expert Review of Medical Devices, 2021
Weyland Cheng, Manye Yao, Bo Zhai, Penggao Wang
A well-known commercial fiber optic CF catheter is the TactiCath™ Quartz catheter (Abbott, Chicago, IL, USA), which incorporates a Fabry-Pérot cavity. Fabry-Pérot interferometry uses multiple-beam interference where phase differences between reflected and transmitted light beams alter according to the distance between two parallel semi-reflective surfaces in the cavity. Multiple reflecting beams interact, producing fringes that vary in intensity based on the distance between the two reflective surfaces. The reflected optical power (Pr) can be expressed as a function of the incident optical power (Pi), the reflectivity of the two surfaces (R1 and R2), and the phase shift (φ) from one reflective surface to the other (see Figure 2).[28]:
Manual interferometric device for routine non-invasive tear film break-up time assessment
Published in Seminars in Ophthalmology, 2021
Sania Vidas Pauk, Igor Petriček, Martina Tomić, Tomislav Bulum, Sonja Jandroković, Miro Kalauz, Sanja Masnec, Tomislav Jukić
The lipid layer, lit by white light, appears in colored fringes that occur from interference between light reflected from the lipid layer’s surface and form the interface between that layer and the tear film’s aqueous layer. The method is called interferometry. Semiquantitative interferometry, introduced by Norn in 1979, was performed by placing the small opaque glass in the slit lamplight.27 However, the corneal lipid layer area’s size visualized this way is quite insufficient for adequate assessment of the lipid layer. While commonly used to assess tear lipid layer thickness, interferometry can also be used to measure NIBUT, the time between the last blink and the appearance of the first lipid layer discontinuity.28 Over time, many instruments and prototypes of interferometer have been developed, and the most used for lipid layer analysis and NIBUT measurement was Keeler Tearscope presented by Guillon JP.15,29