An overview of methods to mitigate artifacts in optical coherence tomography imaging of the skin

Background: Optical coherence tomography (OCT) of skin delivers three-dimensional images of tissue microstructures. Although OCT imaging offers a promising high-resolution modality, OCT images suffer from some artifacts that lead to misinterpretation of tissue structures. Therefore, an overview of methods to mitigate artifacts in OCT imaging of the skin is of paramount importance. Speckle, intensity decay, and blurring are three major artifacts in OCT images. Speckle is due to the low coherent light source used in the configuration of OCT. Intensity decay is a deterioration of light with respect to depth, and blurring is the consequence of deficiencies of optical components. Method: Two speckle reduction methods (one based on artificial neural network and one based on spatial compounding), an attenuation compensation algorithm (based on Beer-Lambert law) and a deblurring procedure (using deconvolution), are described. Moreover, optical properties extraction algorithm based on extended Huygens-Fresnel (EHF) principle to obtain some additional information from OCT images are discussed. Results: In this short overview, we summarize some of the image enhancement algorithms for OCT images which address the abovementioned artifacts. The results showed a significant improvement in the visibility of the clinically relevant features in the images. The quality improvement was evaluated using several numerical assessment measures. Conclusion: Clinical dermatologists benefit from using these image enhancement algorithms to improve OCT diagnosis and essentially function as a noninvasive optical biopsy

Removing striping artifacts in light-sheet fluorescence microscopy: a review

In recent years, light-sheet fluorescence microscopy (LSFM) has found a broad application for imaging of diverse biological samples, ranging from sub-cellular structures to whole animals, both in-vivo and ex-vivo, owing to its many advantages relative to point-scanning methods. By providing the selective illumination of sample single planes, LSFM achieves an intrinsic optical sectioning and direct 2D image acquisition, with low out-of-focus fluorescence background, sample photo-damage and photo-bleaching. On the other hand, such an illumination scheme is prone to light absorption or scattering effects, which lead to uneven illumination and striping artifacts in the images, oriented along the light sheet propagation direction. Several methods have been developed to address this issue, ranging from fully optical solutions to entirely digital post-processing approaches. In this work, we present them, outlining their advantages, performance and limitations

Femtosecond laser micro-inscription of optical coherence tomography resolution test artifacts

Optical coherence tomography (OCT) systems are becoming more commonly used in biomedical imaging and, to enable continued uptake, a reliable method of characterizing their performance and validating their operation is required. This paper outlines the use of femtosecond laser subsurface micro-inscription techniques to fabricate an OCT test artifact for validating the resolution performance of a commercial OCT system. The key advantage of this approach is that by utilizing the nonlinear absorption a three dimensional grid of highly localized point and line defects can be written in clear fused silica substrates

Computational aberration correction in optical coherence tomography with phase-unstable systems

La tomografía de coherence óptica (OCT) es una técnica usada ampliamente en medicina, pero al tratarse de una técnica óptica es susceptible la aberraciones ópticas que degradan la calidad de la imagen, lo que dificulta la visualización de estructuras finas con alta resolución. Este trabajo presenta una técnica computacional para corregir aberraciones en OCT, cuya operación es compatible con muchos tipos de sistemas estandarés, y se muestran resultados en imagen del ojo, la via area y la piel.Optical coherence tomography (OCT) is an imaging technique widely use in medicine. OCT is an optical technique, therefore it is prone to optical aberrations that degrade image quality, making it difficult to visualize fine structures with high resolution.This work presents SHARP, a computational technique for correction of aberrations in OCT, that is compatible with most standard systems, and we present results in eye, airway and skin imagin

Mathematical Modelling of Optical Coherence Tomography

In this chapter a general mathematical model of Optical Coherence Tomography (OCT) is presented on the basis of the electromagnetic theory. OCT produces high resolution images of the inner structure of biological tissues. Images are obtained by measuring the time delay and the intensity of the backscattered light from the sample considering also the coherence properties of light. The scattering problem is considered for a weakly scattering medium located far enough from the detector. The inverse problem is to reconstruct the susceptibility of the medium given the measurements for different positions of the mirror. Different approaches are addressed depending on the different assumptions made about the optical properties of the sample. This procedure is applied to a full field OCT system and an extension to standard (time and frequency domain) OCT is briefly presented.Comment: 28 pages, 5 figures, book chapte

Improving Range Estimation of a 3D FLASH LADAR via Blind Deconvolution

The purpose of this research effort is to improve and characterize range estimation in a three-dimensional FLASH LAser Detection And Ranging (3D FLASH LADAR) by investigating spatial dimension blurring effects. The myriad of emerging applications for 3D FLASH LADAR both as primary and supplemental sensor necessitate superior performance including accurate range estimates. Along with range information, this sensor also provides an imaging or laser vision capability. Consequently, accurate range estimates would also greatly aid in image quality of a target or remote scene under interrogation. Unlike previous efforts, this research accounts for pixel coupling by defining the range image mathematical model as a convolution between the system spatial impulse response and the object (target or remote scene) at a particular range slice. Using this model, improved range estimation is possible by object restoration from the data observations. Object estimation is principally performed by deriving a blind deconvolution Generalized Expectation Maximization (GEM) algorithm with the range determined from the estimated object by a normalized correlation method. Theoretical derivations and simulation results are verified with experimental data of a bar target taken from a 3D FLASH LADAR system in a laboratory environment. Additionally, among other factors, range separation estimation variance is a function of two LADAR design parameters (range sampling interval and transmitted pulse-width), which can be optimized using the expected range resolution between two point sources. Using both CRB theory and an unbiased estimator, an investigation is accomplished that finds the optimal pulse-width for several range sampling scenarios using a range resolution metric

Imagen cuantitativa en microscopia 3D con iluminación parcialmente coherente

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Óptica, leída el 28/01/2021The main research objective of this work is to develop and implement a fast and high resolution technique for reconstructing the 3D refractive index (RI) of weakly absorbing samples. This technique is based on the generalization of optical diffraction tomography (ODT), developed for coherent sample illumination (C-ODT), to the partially coherent case (PC-ODT). In contrast to C-ODT, which involves a specially designed holographic microscope, the proposed PC-ODT technique is implemented in conventional wide-field microscope. The incorporation of the required refocusing module is easy and can be done by a final user unfamiliar with optics (i.e. clinicians and biologists). The low coherent illumination provided by high numerical aperture condenser results in high resolution and reduced speckle noise typical for laser sources used in C-ODT...El principal objetivo de esta tesis es desarrollar e implementar una técnica rápida y de alta resolución para la reconstrucción del índice de refracción (IR) 3D de muestras de absorción débil, basada en la generalización de la tomografía de difracción óptica (TDO), desarrollada para iluminación coherente (TDO-C), al caso parcialmente coherente (TDOPC), lo que evita el ruido coherente y otros artefactos de la iluminación coherente (láser). Al contrario que la TDO-C, que requiere microscopios holográficos (típicamente en configuraciones interferométricas fuera de eje), la técnica TDO-PC propuesta se implementa en un microscopio de campo amplio. La incorporación del módulo de reenfoque óptico es sencillo y puede ser realizado por un usuario no familiarizado con la óptica (como médicos y biólogos). La iluminación poco coherente proporcionada por un condensador de alta apertura numérica logra una alta resolución y reducción del ruido coherente (speckle) típico de las fuentes láser utilizadas en TDO-C...Fac. de Ciencias FísicasTRUEunpu

Focal Modulation Microscopy: A Novel Optical Imaging Method

Ph.DDOCTOR OF PHILOSOPH

Optical Coherence Tomography and Its Non-medical Applications

Optical coherence tomography (OCT) is a promising non-invasive non-contact 3D imaging technique that can be used to evaluate and inspect material surfaces, multilayer polymer films, fiber coils, and coatings. OCT can be used for the examination of cultural heritage objects and 3D imaging of microstructures. With subsurface 3D fingerprint imaging capability, OCT could be a valuable tool for enhancing security in biometric applications. OCT can also be used for the evaluation of fastener flushness for improving aerodynamic performance of high-speed aircraft. More and more OCT non-medical applications are emerging. In this book, we present some recent advancements in OCT technology and non-medical applications

Restoration of optical coherence tomography image data

Restaurace obrazových dat se stala nedílnou součástí procesu zpracování medicínských obrazů získaných libovolným systémem. Stejně tomu je i v případě Optické koherenční tomografie. Cílem této práce je zaprvé prostudování restauračních metod. Za druhé, popis principu zobrazení dat z Optické koherenční tomografie a následné diskuse, které restaurační metody na bázi dekonvoluce by potencionálně našly uplatnění ve zpracování dat z Optické koherenční tomografie. Konečně za třetí, vytvoření programového řešení restauračního procesu OCT dat v prostředí MATLAB a následná diskuze účinnosti prezentovaných řešení.Restoration of image data has become an essential part of the processing of medical images obtained by any system. The same applies in the case of optical coherence tomography. The aim of this work is to study the first restoration methods. Second, the description of the data representation from optical coherence tomography and subsequent discussions that restoration methods based on deconvolution would potentially find application in processing of Optical coherence tomography. Finally, the third to create a program solution of the OCT data restoration process in MATLAB environment and followed by discussion of effectiveness of the presented solutions.