Showing papers on "Optical tomography published in 2021"

Infrared upconversion imaging in nonlinear metasurfaces

Abstract: Infrared imaging is a crucial technique in a multitude of applications, including night vision, autonomous vehicle navigation, optical tomography, and food quality control. Conventional infrared imaging technologies, however, require the use of materials such as narrow bandgap semiconductors, which are sensitive to thermal noise and often require cryogenic cooling. We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas, using a nonlinear wave-mixing process. We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation. In this process, an infrared image of a target is mixed inside the metasurface with a strong pump beam, translating the image from the infrared to the visible in a nanoscale ultrathin imaging device. Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.

Infrared up-conversion imaging in nonlinear metasurfaces

Abstract: Infrared imaging is a crucial technique in a multitude of applications, including night vision, autonomous vehicles navigation, optical tomography, and food quality control. Conventional infrared imaging technologies, however, require the use of materials like narrow-band gap semiconductors which are sensitive to thermal noise and often require cryogenic cooling. Here, we demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas, using a nonlinear wave-mixing process. We experimentally show the up-conversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation. In this process, an infrared image of a target is mixed inside the metasurface with a strong pump beam, translating the image from infrared to the visible in a nanoscale ultra-thin imaging device. Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.

Optical tomography in additive manufacturing: a review, processes, open problems, and new opportunities

Abstract: Additive manufacturing is the process of producing three-dimensional objects in a layer-by-layer technique. Due to its ability to produce complex parts directly without any additional machining, it has found a valuable place in the manufacturing sector of the industry with applications ranging from producing minutely detailed body implants to the nose of spacecrafts. Different types and processes of additive manufacturing will be discussed. Since many shapes and complexities can be produced, it is difficult to test these products for defects using conventional methods. To overcome this difficulty and to analyze the parts nondestructively, optical tomography is used. A detailed study of optical tomography is done. We will be surveying how this method helps identify the porosity and defects in additively manufactured parts nondestructively, making this method efficient and economical. This paper will discuss the advantages of using optical tomography to analyze different materials used in additive manufacturing.

Temperature field reconstruction of 3D luminous flames based on light field tomography theory

Abstract: Standard plenoptic camera can be used to capture multi-dimensional radiation information of high temperature luminous flame to reconstruct the temperature distribution. In this study, a novel method for reconstructing three-dimensional temperature field is proposed. This method is based on the optical tomography combined with standard plenoptic camera. The flame projection information from different planes is contained in one radiation image. In this model, we introduced the effective concept of the nearest neighbor method in the frequency domain to strip the interference of redundant information in the projection and to realize three-dimensional deconvolution. The flame emission intensity received by the pixels on the charge-coupled device sensor can be obtained according to the optical tomographic model. The temperature distributions of the axisymmetric and non-axisymmetric flames can be reconstructed by solving the mathematical model with the nearest neighbor method. The numerical results show that three-dimensional temperature fields of high temperature luminous flames can be retrieved, proving the validity of the proposed method.

Detecting mouse squamous cell carcinoma from submicron full-field optical coherence tomography images by deep learning.

Abstract: The standard medical practice for cancer diagnosis requires histopathology, which is an invasive and time-consuming procedure. Optical coherence tomography (OCT) is an alternative that is relatively fast, noninvasive, and able to capture three-dimensional structures of epithelial tissue. Unlike most previous OCT systems, which cannot capture crucial cellular-level information for squamous cell carcinoma (SCC) diagnosis, the full-field OCT (FF-OCT) technology used in this paper is able to produce images at sub-micron resolution and thereby facilitates the development of a deep learning algorithm for SCC detection. Experimental results show that the SCC detection algorithm can achieve a classification accuracy of 80% for mouse skin. Using the sub-micron FF-OCT imaging system, the proposed SCC detection algorithm has the potential for in-vivo applications.

Focused x-ray luminescence imaging system for small animals based on a rotary gantry.

Abstract: Significance: The ability to detect and localize specific molecules through tissue is important for elucidating the molecular basis of disease and treatment. Unfortunately, most current molecular imaging tools in tissue either lack high spatial resolution (e.g., diffuse optical fluorescence tomography or positron emission tomography) or lack molecular sensitivity (e.g., micro-computed tomography, μCT). X-ray luminescence imaging emerged about 10 years ago to address this issue by combining the molecular sensitivity of optical probes with the high spatial resolution of x-ray imaging through tissue. In particular, x-ray luminescence computed tomography (XLCT) has been demonstrated as a powerful technique for the high-resolution imaging of deeply embedded contrast agents in three dimensions (3D) for small-animal imaging. Aim: To facilitate the translation of XLCT for small-animal imaging, we have designed and built a small-animal dedicated focused x-ray luminescence tomography (FXLT) scanner with a μCT scanner, synthesized bright and biocompatible nanophosphors as contrast agents, and have developed a deep-learning-based reconstruction algorithm. Approach: The proposed FXLT imaging system was designed using computer-aided design software and built according to specifications. NaGdF4 nanophosphors doped with europium or terbium were synthesized with a silica shell for increased biocompatibility and functionalized with biotin. A deep-learning-based XLCT image reconstruction was also developed based on the residual neural network as a data synthesis method of projection views from few-view data to enhance the reconstructed image quality. Results: We have built the FXLT scanner for small-animal imaging based on a rotational gantry. With all major imaging components mounted, the motor controlling the gantry can be used to rotate the system with a high accuracy. The synthesized nanophosphors displayed distinct x-ray luminescence emission, which enables multi-color imaging, and has successfully been bound to streptavidin-coated substrates. Lastly, numerical simulations using the proposed deep-learning-based reconstruction algorithm has demonstrated a clear enhancement in the reconstructed image quality. Conclusions: The designed FXLT scanner, synthesized nanophosphors, and deep-learning-based reconstruction algorithm show great potential for the high-resolution molecular imaging of small animals.

Temporal Imaging for Ultrafast Spectral-Temporal Optical Signal Processing and Characterization

Abstract: Temporal imaging is one of the most promising all-optical signal processing techniques that enable single-shot ultrafast signal characterization in both spectral and temporal domains. However, conventional temporal imaging systems have inherent constraints such as limited record length, narrow spectral observation range and complex system configuration, which prevent their potential to be fully unleashed. In this article, we review the recent efforts in developing advanced temporal imaging systems with much enhanced performance. Their powerful applications are demonstrated by real-time single-shot characterization of Kerr soliton generation in microresonator, noise-like pulses in mode-locked fiber lasers, broadband frequency combs and the dynamic waveform in ultrafast optical tomography. In addition, potential future developments of this technique in several important directions are discussed.

Hyperspectral Three-Dimensional Fluorescence Imaging Using Snapshot Optical Tomography.

Abstract: Hyperspectral three-dimensional (3D) imaging can provide both 3D structural and functional information of a specimen. The imaging throughput is typically very low due to the requirement of scanning mechanisms for different depths and wavelengths. Here we demonstrate hyperspectral 3D imaging using Snapshot projection optical tomography (SPOT) and Fourier-transform spectroscopy (FTS). SPOT allows us to instantaneously acquire the projection images corresponding to different viewing angles, while FTS allows us to perform hyperspectral imaging at high spectral resolution. Using fluorescent beads and sunflower pollens, we demonstrate the imaging performance of the developed system.

Three-compartment-breast (3CB) prior-guided diffuse optical tomography based on dual-energy digital breast tomosynthesis (DBT)

Abstract: Diffuse optical tomography (DOT) is a non-invasive functional imaging modality that uses near-infrared (NIR) light to measure the oxygenation state and the concentration of hemoglobin. By complementarily using DOT with other anatomical imaging modalities, physicians can diagnose more accurately through additional functional image information. In breast imaging, diagnosis of dense breasts is often challenging because the bulky fibrous tissues may hinder the correct tumor characterization. In this work, we proposed a three-compartment-breast (3CB) decomposition-based prior-guided optical tomography for enhancing DOT image quality. We conjectured that the 3CB prior would lead to improvement of the spatial resolution and also of the contrast of the reconstructed tumor image, particularly for the dense breasts. We conducted a Monte-Carlo simulation to acquire dual-energy X-ray projections of a realistic 3D numerical breast phantom and performed digital breast tomosynthesis (DBT) for setting up a 3CB model. The 3CB prior was then used as a structural guide in DOT image reconstruction. The proposed method resulted in the higher spatial resolution of the recovered tumor even when the tumor is surrounded by the fibroglandular tissues compared with the typical two-composition-prior method or the standard Tikhonov regularization method.

Types/Applications of Photoacoustic Contrast Agents: A Review

Abstract: Ultrasound imaging, one of the common diagnosis techniques, is frequently used since it is safe, cost-efficient technique and real-time imaging can be conducted. However, various organs and tissues reflect ultrasonic waves, which leads to difficulty in imaging small biomolecules and to a low spatial resolution for deep-tissue images. As such, there have been significant advances in photonics and optical molecular probes in recent years, and photoacoustic (PA) tomography (PAT) has emerged as a promising modality that can overcome the limitations of ultrasound. PAT relies on the photoacoustic effect, which is the conversion of absorbed optical energy into acoustic energy. Since fewer biomolecules exhibit the photoacoustic effect compared to the scattering or reflection of ultrasound, PAT can be employed to generate high-resolution images. PAT also has a number of other advantages when compared to conventional biomedical imaging modalities such as optical tomography, ultrasound imaging, computed tomography, positron emission tomography and magnetic resonance imaging. This review provides a general overview of the contrast agents used for PAT, including organic, inorganic and hybrid contrast agents, and describes their application. This review also identifies limitations of current PAT contrast agents and suggests future research directions for their development.

Acousto-optic interaction strengths in optically scattering media using high pressure acoustic pulses

Abstract: Ultrasound optical tomography (UOT) is a developing medical imaging technique with the potential to noninvasively image tissue oxygenation at depths of several centimeters in human tissue. To accurately model the UOT imaging, it is necessary the calculate the signal produced by the interaction between ultrasound and light in the scattering medium. In this paper we present a rigorous description for modeling this process for ultrasound pulses in the non-linear regime with peak pressures ranging up to the medical safety limit. Simulation results based on the presented model agree well with measurements performed with fully characterized ultrasound pulses. Our results also indicate that the UOT modeling process can be accurately simplified by disregarding the acoustically induced movement of scatterers. Our results suggest that the explored model and its software implementation can be used as a virtual lab to aid future development of pulses and UOT imaging algorithms.

Snapshot Three-Dimensional Absorption Imaging of Microscopic Specimens

Abstract: Snapshot projection optical tomography (SPOT) uses a microlens array (MLA) to simultaneously capture the projection images of a three-dimensional (3D) specimen corresponding to different viewing directions. Compared to other light-field imaging techniques using an MLA, SPOT is dual telecentric and can block high-angle stray rays without sacrificing the light collection efficiency. Using SPOT, we recently demonstrated snapshot 3D fluorescence imaging. Here we demonstrate snapshot 3D absorption imaging of microscopic specimens. For the illumination, we focus the incoherent light from a light-emitting diode onto a pinhole, which is placed at a conjugate plane to the sample plane. SPOT allows us to capture the ray bundles passing through the specimen along different directions. The images recorded by an array of lenslets can be related to the projections of 3D absorption coefficient along the viewing directions of lenslets. Using a tomographic reconstruction algorithm, we obtain the 3D map of absorption coefficient. We apply the developed system to different types of samples, which demonstrates the optical sectioning capability. The transverse and axial resolutions measured with gold nanoparticles are 1.3 and 2.3 $\ensuremath{\mu}\mathrm{m}$, respectively.

Pulse-sheet chemical tomography by counterpropagating stimulated Raman scattering

Abstract: Large-volumetric optical tomography with molecular specificity has long been pursued to tackle the challenge of dissecting both structural and chemical organization of complicated biological tissues. Here, based on counterpropagating femtosecond pulse laser trains and stimulated Raman scattering, we report pulse-sheet chemical tomography (PCT), which allows label-free bond-selective three-dimensional imaging of large intact tissues. To prove the concept, we demonstrate vibrational tomography of highly scattering bone tissue with lateral resolution of 16.4 µm and axial resolution of 24.5 µm, over a large field of view of 8×8×1.6mm3 in a mouse skull with scalp. PCT resolves the trade-off between focal depth and spatial resolution, and offers unique biomedical and clinical prospects for optical tomography of tissues and organs in the future.

Ultrasound modulated bioluminescence tomography with a single optical measurement

Abstract: Ultrasound modulated bioluminescence tomography (UMBLT) is an imaging method which can be formulated as a hybrid inverse source problem. In the regime where light propagation is modeled by a radiative transfer equation, previous approaches to this problem require large numbers of optical measurements [10]. Here we propose an alternative solution for this inverse problem which requires only a single optical measurement in order to reconstruct the isotropic source. Specifically, we derive two inversion formulae based on Neumann series and Fredholm theory respectively, and prove their convergence under sufficient conditions. The resulting numerical algorithms are implemented and experimented to reconstruct both continuous and discontinuous sources in the presence of noise.

Prospects for multimodal visualisation of biological tissues using fluorescence imaging

Abstract: We investigate skin optical clearing in laboratory animals ex vivo and in vivo by means of low-molecular-weight paramagnetic contrast agents used in magnetic resonance imaging (MRI) and a radiopaque agent used in computed tomography (CT) to increase the sounding depth and image contrast in the methods of fluorescence laser imaging and optical coherence tomography (OCT). The diffusion coefficients of the MRI agents Gadovist®, Magnevist®, and Dotarem®, which are widely used in medicine, and the Visipaque® CT agent in ex vivo mouse skin, are determined from the collimated transmission spectra. MRI agents Gadovist® and Magnevist® provide the greatest optical clearing (optical transmission) of the skin, which allowed: 1) an almost 19-fold increase in transmission at 540 nm and a 7 – 8-fold increase in transmission in the NIR region from 750 to 900 nm; 2) a noticeable improvement in OCT images of skin architecture; and 3) a 5-fold increase in the ratio of fluorescence intensity to background using TagRFP-red fluorescent marker protein expressed in a tumour, after application to the skin of animals in vivo for 15 min. The obtained results are important for multimodal imaging of tumours, namely, when combining laser fluorescence and OCT methods with MRI and CT, since the contrast agents under study can simultaneously enhance the contrast of several imaging methods.

Plankton reconstruction through robust statistical optical tomography.

Abstract: Plankton interact with the environment according to their size and three-dimensional (3D) structure. To study them outdoors, these translucent specimens are imaged in situ. Light projects through a specimen in each image. The specimen has a random scale, drawn from the population’s size distribution and random unknown pose. The specimen appears only once before drifting away. We achieve 3D tomography using such a random ensemble to statistically estimate an average volumetric distribution of the plankton type and specimen size. To counter errors due to non-rigid deformations, we weight the data, drawing from advanced models developed for cryo-electron microscopy. The weights convey the confidence in the quality of each datum. This confidence relies on a statistical error model. We demonstrate the approach on live plankton using an underwater field microscope.

Fast three-dimensional focused x-ray luminescence computed tomography

Abstract: X-ray luminescence computed tomography (XLCT) imaging is a hybrid molecular imaging modality combining the merits of both conventional x-ray imaging (high spatial resolution) and optical imaging (high measurement sensitivity). The narrow x-ray beam based XLCT imaging has been shown to be promising. However due to the selective excitation scheme, the imaging speed is slow thus limiting its practical applications for in vivo imaging. In this work, we have introduced a continuous scanning scheme to acquire data for each angular projection in one motion, eliminating the previous stepping scheme and reducing the data acquisition time, which makes it feasible for multiple transverse scans for three-dimensional (3D) imaging. We have introduced a high accuracy vertical stage to our focused x-ray beam based XLCT imaging system to perform high-resolution and 3D XLCT imaging. We have also included a scintillator crystal coupled to a PMT to act as a single-pixel detector for boundary detection purposes to replace our previous flat panel x-ray detector. We have verified the feasibility of our proposed scanning scheme and imaging system by performing phantom experimental studies. A phantom was embedded with a set of cylindrical targets with 200 μm edge-to-edge distance and was scanned in our imaging system with the proposed method. To test the feasibility for 3D scanning, we took measurements from 4 transverse slices with a vertical step size of 1 mm. The results of the experiments verified the feasibility of our proposed method to perform 3D XLCT imaging using a narrow x-ray beam in a reasonable time.

Single-shot ultrasound-modulated optical tomography with enhanced speckle contrast.

Abstract: Ultrasound-modulated optical tomography (UOT) images optical contrast deep inside biological tissue. Among existing approaches, camera-based parallel detection is beneficial in modulation depth but is limited to the relatively slow framerate of cameras. This condition prevents such a scheme from achieving maturity to image live animals with sub-millisecond speckle correlation time. In this work, we developed on-axis single-shot UOT by investigating the statistics of speckles, breaking the restriction imposed by the slow camera framerate. As a proof of concept, we experimentally imaged a one-dimensional absorptive object buried inside a moving scattering medium with speckle correlation time down to 0.48 ms. We envision that this single-shot UOT is promising to cope with live animals with fast speckle decorrelation.

Optical tomography dynamic for time-dependent coherent states generated by an open qubit-cavity system

Abstract: Optical tomography is investigated for time-dependent quantum states, which are generated from coherent even and odd coherent cavity fields interacting with a two-level system (qubit) in the presence of phase damping. The effects of the qubit-cavity coupling, detuning, and cavity phase damping on the optical tomography distribution are studied. The dynamics of the optical tomography is explored for an open cavity field. We show an aspect of the alteration of the optical tomography distribution.

Quantitative spectroscopic comparison of the optical properties of mouse cochlea microstructures using optical coherence tomography at 1.06 µm and 1.3 µm wavelengths.

Abstract: Currently, the cochlear implantation procedure mainly relies on using a hand lens or surgical microscope, where the success rate and surgery time strongly depend on the surgeon’s experience. Therefore, a real-time image guidance tool may facilitate the implantation procedure. In this study, we performed a systematic and quantitative analysis on the optical characterization of ex vivo mouse cochlear samples using two swept-source optical coherence tomography (OCT) systems operating at the 1.06-µm and 1.3-µm wavelengths. The analysis results demonstrated that the 1.06-µm OCT imaging system performed better than the 1.3-µm OCT imaging system in terms of the image contrast between the cochlear conduits and the neighboring cochlear bony wall structure. However, the 1.3-µm OCT imaging system allowed for greater imaging depth of the cochlear samples because of decreased tissue scattering. In addition, we have investigated the feasibility of identifying the electrode of the cochlear implant within the ex vivo cochlear sample with the 1.06-µm OCT imaging. The study results demonstrated the potential of developing an image guidance tool for the cochlea implantation procedure as well as other otorhinolaryngology applications.

Uniqueness, Lipschitz Stability, and Reconstruction for the Inverse Optical Tomography Problem

Abstract: In this paper, we consider the inverse problem of recovering a diffusion $\sigma$ and absorption coefficients $q$ in a steady-state optical tomography problem from the Neumann-to-Dirichlet map. We ...

Analysis of Retinal Layers in Fibromyalgia Patients with Premium Protocol in Optical Tomography Coherence and Quality of Life.

Abstract: To evaluate the inner retinal layers in fibromyalgia (FM) patients compared to control subjects using posterior pole protocol (PPole) analysis in optical coherence tomography (OCT) and to correlate...

Longitudinal Spatial Coherence Gated Optical Tomography and Topography

Abstract: We reported the application of longitudinal spatial coherence (LSC) properties of a pseudo thermal light source for the topography and tomography of multilayered objects. To synthesize the pseudo thermal light source, He–Ne laser (632.8 nm) is passed through a rotating diffuser and multi-multimode fiber bundle. We demonstrated the topography of gauge block with height difference of 20 µm and the tomography of RBC and onion cell slice placed onto one another. The higher axial resolution is achieved for sectioning due to LSC property of the light source which is otherwise not possible by means of purely temporal coherence property of He–Ne laser.

Numerical reconstruction of turbid slab optical properties using global optimization algorithms.

Abstract: The detection and reconstruction of the optical properties within turbid slabs/plate parallel mediums have been widely investigated for its applications in medical diagnosis, atmosphere detection, etc., where the scattering of light would be expected. Although the scattering signal can be utilized for diagnostics purposes, the multiple scattering in the intermediate scattering regime (with an optical depth ~ 2–9) has posed a remarkable challenge. Existing optical tomography methods usually only reconstruct the reduced scattering coefficient to investigate the properties of the scattering target, while reconstruction efforts in analyzing the exact scattering phase function are rare. Solving such issues can provide much more information for proper interpretation of the characteristics of the turbid slab. This work demonstrates an inversion method based on optimization algorithms and the angular distribution of the transmitted light at the entrance plane and the exit plane of the sought medium. Candidate phase functions were pre-calculated and the optimization algorithm is able to reconstruct the phase function spatial distribution of the turbid slab with a satisfactory computational cost. Parametric studies were also performed to analyze the performance of each optimization algorithm used and the sensitivity of this Markov reconstruction scheme to noise.

In Phantom Validation of Time-Domain Near-Infrared Optical Tomography Pioneer for Imaging Brain Hypoxia and Hemorrhage.

Abstract: The neonatal brain is a vulnerable organ, and lesions due to hemorrhage and/or ischemia occur frequently in preterm neonates. Even though neuroprotective therapies exist, there is no tool available to detect the ischemic lesions. To address this problem, we have recently designed and built the new time-domain near-infrared optical tomography (TD NIROT) system – Pioneer. Here we present the results of a phantom study of the system performance. We used silicone phantoms to mimic risky situations for brain lesions: hemorrhage and hypoxia. Employing Pioneer, we were able to reconstruct accurately both position and optical properties of these inhomogeneities.

Learn an index operator by CNN for solving diffusive optical tomography: a deep direct sampling method

Abstract: In this work, we investigate the diffusive optical tomography (DOT) problem in the case that limited boundary measurements are available. Motivated by the direct sampling method (DSM), we develop a deep direct sampling method (DDSM) to recover the inhomogeneous inclusions buried in a homogeneous background. In this method, we design a convolutional neural network (CNN) to approximate the index functional that mimics the underling mathematical structure. The benefits of the proposed DDSM include fast and easy implementation, capability of incorporating multiple measurements to attain high-quality reconstruction, and advanced robustness against the noise. Numerical experiments show that the reconstruction accuracy is improved without degrading the efficiency, demonstrating its potential for solving the real-world DOT problems.

A homogenized cerebrospinal fluid model for diffuse optical tomography in the neonatal head.

Abstract: Diffuse optical tomography is a non-invasive and non-irradiating medical imaging technique that is particularly suitable for cerebral monitoring of newborns since it can be used at the bedside of the patient. Here, a new model for optical tomography in the neonatal brain is presented that takes into account the presence of arachnoid trabeculae in the cerebrospinal fluid (CSF). It is known that the classical diffusion approximation (DA) for light propagation is at the limit of validity in the CSF layer due to the low values of the absorption and scattering coefficients. The new model is obtained by the DA of the homogenized radiative transfer equation and is rigorously justified. Numerical results in two and three dimensions attest for the improved sensitivity of the new model to the presence of perturbations in the brain layer.

A simple and low cost USB webcam-driven optical tomography system suitable for teaching x-ray computed tomography

Abstract: A simple and cheap optical analog computed tomography (CT) system, useful for teaching x-ray CT for physics, medical physics and engineering physics students without applying ionizing radiation is presented. White spectrum of a light emitting diode (LED) source was characterized by using an in-house constructed spectrophotometer. A simple electronic hardware, utilizing a synchronization of an universal serial bus webcam and direct current (DC) motor was developed in such a way that, a single click on the record video button of the webcam software is enough to run the tomograph. Finally, the two- and three-dimensional tomography reconstructions are briefly discussed and presented.