New intravascular imaging techniques (optical coherence tomography”OCT” and optical frequency domain imaging”OFDI”)
Ever D. Grech in Practical Interventional Cardiology, 2017
The very short wave length of light leads to extremely high speed of light compared with ultrasound, which represents the fundamental difference between optical and ultrasound-based imaging. In tissues, the speed of light is nearly 3 × 108 m/s compared with 1500 m/s for ultrasound. The ideal resolution for intravascular ultrasound (IVUS), 100 μm, requires a time delay of 100 nanoseconds to detect sound echoes. This time delay, also called time resolution, is within the range of electronic detection of IVUS machines. On the other hand, the detection of light echoes requires much higher time resolution. A time resolution of ~30 femtoseconds (3 × 1015 seconds) is required for measurement of distances with a 10 μm resolution, the typical resolution for OCT imaging. Accordingly, direct measurement of time delays between optical echoes by usual electronic means is extremely difficult and measurement methods such as interferometry are required for OCT imaging. Interferometry depends on coherence, a physical property of light waves that makes them capable of generating interference when combined.4
All About Wave Equations
Bahman Zohuri, Patrick J. McDaniel in Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information. Interferometry is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy (and its applications to chemistry), quantum mechanics, nuclear and particle physics, plasma physics, remote sensing, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, and optometry.
Techniques Of Hydrophone Calibration
Marvin C. Ziskin, Peter A. Lewin in Ultrasonic Exposimetry, 2020
There are other technical aspects of the interferometer itself, such as the frequency range and response characteristic of the internal optical detectors used, which affect the measurements. The detectors typically set the frequency range of the entire system, and, while adequate up to several tens of megahertz, they do have some variation in response over that range.
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
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]:
Peripheral eye length measurement techniques: a review
Published in Clinical and Experimental Optometry, 2020
Ingrid Ornella Koumbo mekountchou, Fabian Conrad, Padmaja Sankaridurg, Klaus Ehrmann
The first reported measurement of peripheral EL using partial coherence interferometry was by Fercher et al. where they obtained the fundus profile by measuring in steps of 2° from 24° nasal to 22° temporal along the horizontal meridian.1991 At that time, partial coherence interferometry was found to have several advantages compared to A‐scan ultrasonography such as greater longitudinal accuracy and transverse resolution, as well as improved patient comfort and acceptance due to the non‐contact method. Other advantages include the need for only one interferometric measurement to identify path length matching and the insensitivity to small eye movements. However, disadvantages of this technology are its complex interferogram, limited speed and sensitivity of the dual‐beam, the need for additional components, and lower sensitivity.2016 The other drawbacks are that light is strongly attenuated by opaque ocular media, and there are fixation problems that can hinder the measurements.2002 Moreover, the method requires that the experimenter be skilled in checking interference fringes.1993 In addition, measurements with this setup are time‐consuming (the patient needed to look into the ‘laser’ beam the entire time and it took about 15-minutes for one measurement for a skilled operator). Hence, this method was found less applicable for a larger number of patients, especially elderly1991 and young people.
Related Knowledge Centers
- Chemistry
- Holography
- Interactome
- Microfluidics
- Refractive Index
- Spectroscopy
- Optometry
- Optical Path
- Optical Path Length
- Beam Splitter