Coherent Imaging Method Research Articles

In vivo laser computed tomographic imaging of human fingers by coherent detection imaging method using different wavelengths in near infrared region

We report in vivo laser computed tomographic images of the proximal interphalangeal joint region of a healthy human volunteer’s index finger. The laser computed tomographic (CT) images were obtained with a highly sensitive coherent detection imaging method that is based on the optical heterodyne detection method. These laser CT images are compared at the wavelengths of 715 nm and 1.064 μm and with images obtained by conventional imaging methods such as x-ray CT and magnetic resonance imaging. Internal structures of the proximal interphalangeal joint region could be clearly identified in the laser CT images.

Coherent methods in confocal microscopy

The authors review the use of 2 kinds of coherent imaging methods in confocal microscopy: interferometry and the use of optical fibres. In both cases, the emphasis is concerned with detecting both the confocal field amplitude and its phase. It is usual in confocal systems to detect only the image intensity and so to loose all phase information. In order to detect the phase with an incoherent photodetector, it is necessary to use some form of interferometry. In the classical interferometer, the authors show that by detecting the phase and amplitude in a conventional interference microscope employing a large area detector it is possible to obtain confocal imaging. Indeed, the interference term images in conventional and confocal interference microscopes are found to be identical. An optical fibre-based confocal interference microscope is shown to have some practical advantages over a conventional, noncommon path implementation. The question of resolution in phase imaging is discussed and it is shown that due to the inherent nonlinearity of the process, great care should be taken in interpreting these images. The introduction of optical fibres instead of pinholes is shown to lead to simplification in system design. However, the introduction of 2-mode fibres makes the system more versatile. In essence, the fundamental mode detects the image amplitude and the first order mode detects the differential of the image amplitude. These modes then propagate along the fibre with different speeds and, hence, emerge from the fibre with a relative phase difference determined by the length of the fibre. These 2 modes are finally allowed to interfere. In this way, it is possible to obtain both confocal differential amplitude contrast, and differential phase contrast images simultaneously, without any other alteration to the optical system.

Incoherence in atomic-resolution Z-contrast imaging

Incoherent imaging of atomic clusters, monolayer rafts, or low index crystal projections at atomic resolution in a scanning transmission electron microscope (STEM) offers a number of distinct advantages over coherent imaging methods. These include an improved “interpretable” resolution and no experimental contrast reversals with specimen thickness or objective lens defocus. However, considerable controversy and confusion has arisen concerning the conditions under which the image of a given object can be interpreted using incoherent imaging theory. Here, we attempt to clarify the situation.Firstly, we consider the case of very thin specimens, such as heavy atoms, clusters of atoms, or extremely thin crystals. Experimentally, these specimens demand a relatively low annular detector inner radius to achieve an acceptable signal-to-noise ratio in the image. It is usual, therefore, to match the detector inner radius to the radius of the directly transmitted disc. In this conventional geometry, the annular dark-field signal will be dominated by coherent scattering, and the use of incoherent imaging theory may give rise to appreciable error close to the resolution of the STEM instrument.

Coherent imaging methods in ultrasonic defectoscopy (review): Badalyan, V.G. Industrial Laboratory, Vol. 55, No. 11, pp. 1290–1299, (May 1990)

Coherent imaging methods in ultrasonic defectoscopy (review): Badalyan, V.G. Industrial Laboratory, Vol. 55, No. 11, pp. 1290–1299, (May 1990)

Optical computed tomography for biomedical objects based on coherent detection imaging method

AbstractThis paper summarizes a series of studies aiming at realization of computed tomography imaging (CT) by laser beam for actual in vitro biological samples, which is the first successful trial achieved in the world. The method is realized first by image reconstruction, which detects and selects only the weak transmitted light component buried in stronger multiple scattered light, using the optical heterodyne detection with a very high directivity and sensitivity. This is called coherent detection imaging (CDI).To realize the optical CT using the laser light based on the projection theorem, the following three conditions should essentially be satisfied: (1) The direct‐transmitted light component in the biological system with multiple scattering should accurately be selected and detected. (2) The Lambert‐Beer law should be applied to the selectively detected direct‐transmitted light component. (3) There must exist a direct‐transmitted light component in the medium with complex distribution of refraction index as well as complex boundaries. The authors examined the medium in which the sample is buried and cannot be observed, not only by the naked eye but also by the traditional direct detection method. It was verified experimentally that the three conditions for the realization of the optical CT are applicable, and it was demonstrated that optical CT imaging is feasible for actual samples using the CDI method.

Two-dimensional coherent detection imaging in multiple scattering media based on the directional resolution capability of the optical heterodyne method

This paper describes a new application of optical heterodyne detection using a laser beam for two-dimensional imaging of the internal structure of strongly scattering media in which the structure is completely obstructed from normal visual observation. The directional resolution capability for image formation due to the excellent antenna properties of the heterodyne technique is verified experimentally using a ground glass to cause strong scattering of the signal beam. Successful image detection of a test target placed in a highly scattering absorptive medium, with spatial resolution better than 400 μm in the case of our experiments, demonstrates that this Coherent Detection Imaging (CDI) method can overcome the diffuse nature of images in media such as those of biomedical interest and others to achieve scanning and tomographic imaging.

Coherent Detection Imaging Method Using Lasers. Achievement of Laser CT(Computed Tomography) for Biomedical Applications.

In this paper, we report and discuss the achievment of laser absorption computed tomography of actual in vivo/in vitro biological objects using the Coherent Detection Imaging (CDI) method. This CDI scheme offers the feasible and reliable means for the computer-assisted optical tomographic imaging based on the optical heterodyne technique that has excellent directionality and very high sensitivity. We have experimentally demonstrated the fulfillment of fundamental conditions for the establishment of laser absorption tomography by our novel CDI method in highly scattering and absorptive media such as actual biological tissues and objects. Thus we have realized the tomographic image reconstruction of several biological objects including plant stems, chicken tissue, whole egg, struma specimen and new-born mouse brain employing the projection slice theorem.

Laser Spectroscopic Coputed Topography Using Coherent Detection Imaging Method of Biomedical Applications

In this paper, we reprot the feasible and realible method for the laser absorption computer-assisted tomographic imaging based on the optical heterodyne technique that has very high sensitivity and excellent directivity to distinguish one direction from another. This new method is named the Coherent Detection Imaging (CDI). We have demonstrated experimentally the fulfillment of three fundamental conditions for the establishment of laser absorption computed tomography by means of the optical heterodyne method in biological tissues exhibiting severe multiple light scattering. Thus the first successful imaging by laser absorption computed tomography of In vivo/in vitro biological objects has been achieved utilizing our CDI method and the projection slice theorem.

新しいレーザー生体計測法としての光ヘテロダイン方式CT法の研究開発

This paper reports, we believe for the first time, the basic principle and experimental demonstration of differential absorption computed tomography of Coherent Detection Imaging(CDI) method. Although the CDI scheme offers the feasible and reliable means for optical computed tomographic imaging of in vitro/in vivo biological objects based on the optical heterodyne technique incorporating laser beams, the single laser beam method is difficult to distinguish or to eliminate apparently detected absorption due to multiple scattering from actual absorption distributed inside the object. In order to solve this problem, the differential absorption technique employing the two different-wavelength beams is practically usefull. We performed the experiment using glass phantoms along with red and green beams simultaneously genarated from a He-Cd laser.

Microdifferential holography.

A novel coherent imaging method analogous to electronic differential amplification is described and analyzed. The method is well suited to highlighting local changes in the optical properties of a dynamic object whose more prominent details are largely static. The object may be examined either in transmitted light or in reflected light. The method discriminates between changes that result from substructural reorganization of object details too fine to be imaged as resolved structures and changes that result from the microdisplacement of optically resolved structures. Substructural reorganization is signaled by changes in the amplitude of the transmitted or reflected light, whereas ordinary displacement is displayed in the usual way through a change in phase. The method is capable of detecting displacements as small as several milliwavelengths. Images of contractile activity in muscle are presented that illustrate the method's sensitivity and analytic power.