Vladislav Batshev

Double-AOTF-based aberration-free spectral imaging endoscopic system for biomedical applications

The problem of in vivo photoluminescence diagnostics of the tissues accessible by endoscopes is discussed. The spectral imaging module attachable to conventional rigid and flexible medical endoscopes is developed and described. It is based on a double acousto-optical tunable filter (AOTF) and a specialized optical coupling system. The module provides wide field of view (FOV), absence of image distortions, random spectral access, fast spectral image acquisition at any wavelength in the visible range and accurate measurement of reflectance spectrum in each pixel of the image. Images of typical biomedical samples are presented and discussed. Their spectra are compared to the reference data.

Aberration analysis of AOTF-based spectral imaging systems

Image aberrations caused by acousto-optic (AO) anisotropic diffraction in uniaxial crystals are discussed. For their analysis, we propose a simplified ray-tracing model of an AO crystal cell (AOC). With this approach, one can assign any configuration of AO interaction, any material and geometry of the crystal, and then estimate all conventional ray aberrations, such as spherical, coma, astigmatism, distortion, etc. The optimization procedure is demonstrated by the aberration analysis of three principal spectral imaging schemes based on AO tunable filters (AOTFs). The approach developed promises performance improvement of AOTF-based systems for high-quality spectral imaging and image processing.

Compact AOTF-based spectral imaging system for medical endoscopic analysis

Abstract A prototype of a spectral imaging module is described which can be attached to conventional rigid and flexible medical endoscopes. It is based on acousto-optic tunable filters (AOTF) and provides fast spectral image registration at an arbitrary series of wavelengths. The main advantage of the device is the minimization of spatial and spectral image distortion by use of a specialized double AOTF monochromator. These properties ensure immediate and reliable detection of spectral features in any image pixel. Real-time spectral analysis, in addition to spectral visualization, provides the opportunity to make medical photoluminescence diagnostics more effective. Zusammenfassung Es wird der Prototyp eines spektralen Bildgebungsmoduls beschrieben, das an herkömmliche starre und flexible medizinische Endoskope adaptiert werden kann. Das Modul basiert auf akustooptischen Modulatoren (acousto-optic tunable filters, AOTF) und liefert schnelle Spektralbilder für beliebige Wellenlängen. Der Hauptvorteil liegt dabei in der Minimierung der räumlichen und spektralen Bildverzerrung, was durch die Verwendung eines speziellen Doppel-AOTF-Monochromators erreicht wird. Dies sorgt für die sofortige und zuverlässige Erkennung von spektralen Merkmalen in jedem Bildpunkt. Die Echtzeit-Spektralanalyse, zusätzlich zur spektralen Visualisierung, bietet damit die Möglichkeit die medizinische Photolumineszenz-Diagnostik effektiver zu gestalten.

AOTF-based optical system of a microscope module for multispectral imaging techniques

Multi-spectral imaging techniques are widely used in microscopy for many applications. One of the most widespread spectral elements for this purpose is an imaging acousto-optic tunable filter (AOTF). AOTF-based contrast visualization is especially effective when used together with other imaging techniques. Simultaneous utilization of two or more imagers requires optical coupling to provide point-to-point matching of the obtained images. Small linear and angular aperture of AOTF additionally hampers the development of multi-sensor imaging systems for microscopy. In this paper, we present a compact optical system which allows to integrate AOTF-based spectral imager into the schemes of conventional microscopes and provide high-quality spectral image of the same scale as in another, for example, wideband channel. The effectiveness of the proposed approach is demonstrated experimentally.

Conjugation of fiber-coupled wide-band light sources and acousto-optical spectral elements

Endoscopic instrumentation is widely used for diagnostics and surgery. The imaging systems, which provide the hyperspectral information of the tissues accessible by endoscopes, are particularly interesting and promising for in vivo photoluminescence diagnostics and therapy of tumour and inflammatory diseases. To add the spectral imaging feature to standard video endoscopes, we propose to implement acousto-optical (AO) filtration of wide-band illumination of incandescent-lamp-based light sources. To collect maximum light and direct it to the fiber-optic light guide inside the endoscopic probe, we have developed and tested the optical system for coupling the light source, the acousto-optical tunable filter (AOTF) and the light guide. The system is compact and compatible with the standard endoscopic components.

Determining the aberration characteristics of optical systems containing acousto-optical diffraction elements

We describe a method and present an example of the calculation of aberration images that arise in optical systems (OSs) containing acousto-optical (AO) diffraction elements. The method is based on the integration of existing analytical algorithms into software intended for the automated calculation of classical OSs. The proposed approach can be used for the calculation of aberrations in systems containing AO elements of various configurations and for the optimization of related devices.

Applying a ray tracing model of an optoelectronic system to improve the accuracy of endoscopic measurements

The problem of improving the accuracy and extending the range of geometrical measurements taken by video endoscopes equipped with attachable stereo adapter has been considered. For calibration and measurements, it has been suggested to use a ray tracing model of stereoscopic recording that takes the actual paths of rays in the prism into account. Based upon multiple experiments with test objects, it has been shown that this allows one to reduce the error in measurements of linear dimensions (length and depth) and area. The theoretical conclusions have been confirmed by results obtained when measuring defects in the blades of a jet engine with the use of a real stereoscopic video-endoscopic system.

Design of an optical system for coupling a wideband light source with an acousto-optical tunable filter

We report on the calculation method for the development of fiber-coupled acousto-optical (AO) spectral filtration modules compatible with conventional inexpensive wide-band light sources (incandescent lamps). The formulas for main parameters of the optical systems of such modules are given. Two possible schemes (collimating and telecentric confocal) of AO filtration are discussed and compared. Their optical throughput and aberration parameters are analyzed. The proposed approach may be useful for the tunable light filtration in various applications (microscopy, endoscopy, interferometry, etc.).

Stereoscopic tip for a video endoscope: problems in design

3-dimensional (3D) stereoscopic geometrical measurements of hard-to-reach objects are discussed. Prism-based tips for video endoscopic probes allow registering images from two different viewpoints on a single sensor and applying stereoscopic methods. In this study, we analyze the problems in the optical design of these tips and ways to improve its characteristics. The results may be useful for the development of the new stereoscopic measurement tools for remote visual inspection in industrial and medical applications.