A technique called optical coherence tomography (OCT) has been developed for noninvasive cross-sectional imaging in biological systems. OCT uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging. OCT has longitudinal and lateral spatial resolutions of a few micrometers and can detect reflected signals as small as approximately 10(-10) of the incident optical power. Tomographic imaging is demonstrated in vitro in the peripapillary area of the retina and in the coronary artery, two clinically relevant examples that are representative of transparent and turbid media, respectively.

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Optical coherence tomography

Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.

https://link.springer.com/content/pdf/bfm%3A978-3-319-06419-2%2F1.pdf

Optical Coherence Tomography

We present an improved and extended version of our coarse grained lipid model. The new version, coined the MARTINI force field, is parametrized in a systematic way, based on the reproduction of partitioning free energies between polar and apolar phases of a large number of chemical compounds. To reproduce the free energies of these chemical building blocks, the number of possible interaction levels of the coarse-grained sites has increased compared to those of the previous model. Application of the new model to lipid bilayers shows an improved behavior in terms of the stress profile across the bilayer and the tendency to form pores. An extension of the force field now also allows the simulation of planar (ring) compounds, including sterols. Application to a bilayer/cholesterol system at various concentrations shows the typical cholesterol condensation effect similar to that observed in all atom representations.

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The MARTINI force field : Coarse grained model for biomolecular simulations

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Noncontact, high resolution measurements of anterior eye structures using optical coherence domain reflectometry are described. Distances between intraocular structures are measured by directing a beam of short coherence length light onto the eye and performing an interferometric measurement on the optical group delay of reflected signals. Measurements of corneal thickness, corneal excision depth, and anterior chamber depth are demonstrated in vitro, and the location of tissue boundaries is resolved to within +/- 2 microns. The full-width-half-maximum longitudinal resolution is 10 microns. Sensitivities to reflected signals as small as 10(-10) of the incident power are achieved by heterodyne detection.

Micron-resolution ranging of cornea anterior chamber by optical reflectometry

By exploiting the nanometer sensitivity of the confocal response to the position of an in-focus reflecting surface, we measured the bending rigidity of lipid-bilayer vesicles with a noninvasive all-optical method. The vesicles were weakly deformed with femtonewton optical force, and the bending rigidity was measured continuously from the ${L}_{\ensuremath{\alpha}}$ through the ${P}_{{\ensuremath{\beta}}^{\ensuremath{'}}}$ to the ${L}_{{\ensuremath{\beta}}^{\ensuremath{'}}}$ phases on the same specimen for the first time. The bending modulus is found to increase by an order of magnitude from the ${L}_{\ensuremath{\alpha}}$ phase to the ${L}_{{\ensuremath{\beta}}^{\ensuremath{'}}}$ phase, as a result of the increasing area-compressibility modulus and bilayer thickness. The dips of bending modulus give precisely the main-transition and pretransition temperatures, which supports the recently proposed chain-melting model of pretransition.

All-optical measurements of the bending rigidity of lipid-vesicle membranes across structural phase transitions

Ultrashort pulses are generated in a Ti:Al2O3 laser by using a coupled nonlinear external cavity. The external cavity uses self-phase modulation in an optical fiber to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation. A stable train of chirped 1.4-psec pulses is generated. After dispersive compensation, pulses as short as 200 fsec are obtained.

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity.

Noninterferometric differential confocal microscopy with 2-nm depth resolution

Enhancement of relativistic third-harmonic generation by using a periodic plasma waveguide is achieved. Resonant dependence of harmonic intensity on plasma density modulation parameters is observed, which is a distinct characteristic of quasi-phase matching.

Jyhpyng Wang

Papers

Micron-resolution ranging of cornea anterior chamber by optical reflectometry

All-optical measurements of the bending rigidity of lipid-vesicle membranes across structural phase transitions

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity.

Noninterferometric differential confocal microscopy with 2-nm depth resolution

Enhancement of relativistic harmonic generation by an optically-preformed periodic plasma waveguide