Depth-dependent Dispersion Research Articles

Depth-dependent dispersion compensation for the micron resolution optical coherence tomography with a time-frequency analysis method

In the noninvasive imaging of the samples such as biological tissues with various forms of OCT, the dispersion effect would seriously influence the image contrast and resolution. Compared with the invariant dispersion, the sample-induced dispersion is much more difficult to be compensated because it is depth-dependent. In this work, we proposed a time-frequency analysis method to compensate for the depth-dependent dispersion without the pre-knowledge of the dispersive property of the tissue. With the Radon-Ambiguity transform and the fractional Fourier transform the dispersion amount corresponding to the specific depth could be calculated and compensated. The validity of this algorithm was first demonstrated by the simulation of the compensation of the water-induced dispersion at the micron resolution. Furthermore, the TiO2 phantoms and the fingertip of a healthy human volunteer were measured with the common-path micron resolution optical coherence tomography system. The experimental results revealed that the image resolution acquired by the method proposed could be improved by a factor of 2–3. This work can be helpful for dispersion compensation in other optical fields.

Dispersion correction for optical coherence tomography by the stepped detection algorithm in the fractional Fourier domain

Dispersion in optical coherence tomography (OCT) leads to a series of wavelength-dependent phase distortions, which cause degradation of axial resolution. Due to the lack of prior information or the complexity of an exhaustive search calculation, all-depth dispersion suppression can hardly be realized in practical cases, especially for high-speed processing and irregular-structure samples. This paper explores the understanding of the depth-dependent dispersion in the fractional Fourier domain (FRFD) and addresses a new method for dispersion correction based on the FRFD stepped detection algorithm that is able to adaptively compensate the dispersion at all depths of the sample. For the detection of each dispersion component, a coarse search followed by a localized fine search is presented in our algorithm to reduce the calculation complexity with high accuracy guaranteed. A signal separation method utilizing FRFD filtering is also designed to avoid the interference between the dispersion from different depths of the sample, which allows all-depth dispersion correction. The proposed algorithm is verified to be effective through the stratified media of ZnSe. The application of the proposed algorithm in OCT imaging of onion and human coronary artery also demonstrates the feasibility of our algorithm for dispersion correction in bio-tissues.

Depth-dependent dispersion compensation for full-depth OCT image.

A depth-dependent dispersion compensation algorithm for enhancing the image quality of the Fourier-domain optical coherence tomography (OCT) is presented. The dispersion related with depth in the sample is considered. Using the iterative method, an analytical formula for compensating the depth-dependent dispersion in the sample is obtained. We apply depth-dependent dispersion compensation algorithm to process the phantom images and in vivo images. Using sharpness metric based on variation coefficient to compare the results processed with different dispersion compensation algorithms, we find that the depth-dependent dispersion compensation algorithm can improve image quality at full depth.

Dispersion compensation in Fourier domain optical coherence tomography using the fractional Fourier transform

We address numerical dispersion compensation based on the use of the fractional Fourier transform (FrFT). The FrFT provides a new fundamental perspective on the nature and role of group-velocity dispersion in Fourier domain OCT. The dispersion induced by a 26 mm long water cell was compensated for a spectral bandwidth of 110 nm, allowing the theoretical axial resolution in air of 3.6 μm to be recovered from the dispersion degraded point spread function. Additionally, we present a new approach for depth dependent dispersion compensation based on numerical simulations. Finally, we show how the optimized fractional Fourier transform order parameter can be used to extract the group velocity dispersion coefficient of a material.

Depth-Dependent Dispersion Coefficient for Modeling of Vertical Solute Exchange in a Lake Bed under Surface Waves

Variable pressure at the sediment/water interface due to surface water waves can drive advective flows into or out of the lake bed, thereby enhancing solute transfer between lake water and pore water in the lake bed. To quantify this advective transfer, the two-dimensional (2D) advection-dispersion equation in a lake bed has been solved with spatially and temporally variable pressure at the bed surface. This problem scales with two dimensionless parameters: a “dimensionless wave speed” (W) and a “relative dispersivity” (λ) . Solutions of the 2D problem were used to determine a depth-dependent “vertically enhanced dispersion coefficient” ( DE ) that can be used in a 1D pore-water quality model which in turn can be easily coupled with a lake water quality model. Results of this study include a relationship between DE and the depth below the bed surface for W>50 and λ⩽0.1 . The computational results are compared and validated against a set of laboratory measurements. An application shows that surface waves m...

Optimal wavelength for ultrahigh-resolution optical coherence tomography

The influence of depth dependent dispersion by the main component of biological tissues, water, on the resolution of OCT was studied. Investigations showed that it was possible to eliminate the influence of depth dependent dispersion by water in tissue by choosing a light source with a center wavelength near 1.0 microm. Ultrahigh resolution ophthalmic imaging was performed at this wavelength range with a microstructure fiber light source.

Real-time dispersion compensation in scanning interferometry

We propose and demonstrate a method of real-time dispersion compensation suitable for scanning interferometry and optical coherence tomography. Static grating tilt in a scanning frequency-domain optical delay line is shown to produce dispersion that is linearly proportional to scan position, and we use this property to achieve depth-dependent dispersion compensation during an interferometric scan through a dispersive sample.

Numerical dispersion compensation for Partial Coherence Interferometry and Optical Coherence Tomography

Dispersive samples introduce a wavelength dependent phase distortion to the probe beam. This leads to a noticeable loss of depth resolution in high resolution OCT using broadband light sources. The standard technique to avoid this consequence is to balance the dispersion of the sample byarrangingadispersive materialinthereference arm. However, the impact of dispersion is depth dependent. A corresponding depth dependent dispersion balancing technique is diffcult to implement. Here we present a numerical dispersion compensation technique for Partial Coherence Interferometry (PCI) and Optical Coherence Tomography (OCT) based on numerical correlation of the depth scan signal with a depth variant kernel. It can be used a posteriori and provides depth dependent dispersion compensation. Examples of dispersion compensated depth scan signals obtained from microscope cover glasses are presented.