Imaging Of Biological Tissues Research Articles

Analysis of relative error in perturbation Monte Carlo simulations of radiative transport.

Perturbation and differential Monte Carlo (pMC/dMC) methods, used in conjunction with nonlinear optimization methods, have been successfully applied to solve inverse problems in diffuse optics. Application of pMC to systems over a large range of optical properties requires optimal "placement" of baseline conventional Monte Carlo (cMC) simulations to minimize the pMC variance. The inability to predict the growth in pMC solution uncertainty with perturbation size limits the application of pMC, especially for multispectral datasets where the variation of optical properties can be substantial. We aim to predict the variation of pMC variance with perturbation size without explicit computation of perturbed photon weights. Our proposed method can be used to determine the range of optical properties over which pMC predictions provide sufficient accuracy. This method can be used to specify the optical properties for the reference cMC simulations that pMC utilizes to provide accurate predictions over a desired optical property range. We utilize a conventional error propagation methodology to calculate changes in pMC relative error for Monte Carlo simulations. We demonstrate this methodology for spatially resolved diffuse reflectance measurements with ±20% scattering perturbations. We examine the performance of our method for reference simulations spanning a broad range of optical properties relevant for diffuse optical imaging of biological tissues. Our predictions are computed using the variance, covariance, and skewness of the photon weight, path length, and collision distributions generated by the reference simulation. We find that our methodology performs best when used in conjunction with reference cMC simulations that utilize Russian Roulette (RR) method. Specifically, we demonstrate that for a proximal detector placed immediately adjacent to the source, we can estimate the pMC relative error within 5% of the true value for scattering perturbations in the range of . For a distal detector placed at transport mean free paths relative to the source, our method provides relative error estimates within 20% for scattering perturbations in the range of . Moreover, reference simulations performed at lower values showed better performance for both proximal and distal detectors. These findings indicate that reference simulations utilizing continuous absorption weighting (CAW) with the Russian Roulette method and executed using optical properties with a low ratio spanning the desired range of values, are highly advantageous for the deployment of pMC to obtain radiative transport estimates over a wide range of optical properties.

Far-field mid-infrared microscopy via spatial frequency shifting of evanescent waves in photorefractive nematic liquid crystal.

Mid-infrared wavelength has unique advantages in revealing the nanostructures and molecular vibrational signatures. However, the mid-infrared subwavelength imaging is also limited by diffraction. Here, we propose a scheme for breaking the limitation in mid-infrared imaging. With the assistance of orientational photorefractive grating established in nematic liquid crystal, evanescent waves are efficiently shifted back into the observation window. The visualized propagation of power spectra in k-space also proves this point. The resolution has an improvement about 3.2 times higher than the linear case, showing potentials in various imaging areas, such as biological tissues imaging and label-free chemical sensing.

Photoacoustic microscopy system for biological tissue imaging

A photoacoustic microscopy system was created and examined for biological tissue. Characterization of microphone, laser, and motor stepper was done to get the most appropriate setting for the system. The object table is set in a static state in the scanning process while the radiation sources and detector move in the X-Y direction. The hardware components in this system consist of photoacoustic signal generation components, mechanical components, and photoacoustic signal detection components. The hardware components are integrated and controlled by the computer through the Raspberry-pi microcomputer software. The characterization results of the photoacoustic image system obtained the optimum system setting for detecting biological tissue, namely the frequency of the diode laser in the range of 19 kHz with a duty cycle of 30%, with a minimum motor shift of 0.2 mm. This system can image the same biological tissue as the original sample with good image contrast. The smallest sample that can be scanned is 0.75 mm. The photoacoustic penetration depth is 0.5 mm.

Motionless volumetric structured light sheet microscopy.

To meet the increasing need for low-cost, compact imaging technology with cellular resolution, we have developed a microLED-based structured light sheet microscope for three-dimensional ex vivo and in vivo imaging of biological tissue in multiple modalities. All the illumination structure is generated directly at the microLED panel-which serves as the source-so light sheet scanning and modulation is completely digital, yielding a system that is simpler and less prone to error than previously reported methods. Volumetric images with optical sectioning are thus achieved in an inexpensive, compact form factor without any moving parts. We demonstrate the unique properties and general applicability of our technique by ex vivo imaging of porcine and murine tissue from the gastrointestinal tract, kidney, and brain.

Multi-contrast digital histopathology of mouse organs using quantitative phase imaging and virtual staining.

Quantitative phase imaging (QPI) has emerged as a new digital histopathologic tool as it provides structural information of conventional slide without staining process. It is also capable of imaging biological tissue sections with sub-nanometer sensitivity and classifying them using light scattering properties. Here we extend its capability further by using optical scattering properties as imaging contrast in a wide-field QPI. In our first step towards validation, QPI images of 10 major organs of a wild-type mouse have been obtained followed by H&E-stained images of the corresponding tissue sections. Furthermore, we utilized deep learning model based on generative adversarial network (GAN) architecture for virtual staining of phase delay images to a H&E-equivalent brightfield (BF) image analogues. Using the structural similarity index, we demonstrate similarities between virtually stained and H&E histology images. Whereas the scattering-based maps look rather similar to QPI phase maps in the kidney, the brain images show significant improvement over QPI with clear demarcation of features across all regions. Since our technology provides not only structural information but also unique optical property maps, it could potentially become a fast and contrast-enriched histopathology technique.

Powell lens-based line-field spectral domain optical coherence tomography system for cellular resolution imaging of biological tissue.

A Powell lens is used in a line-field spectral domain OCT (PL-LF-SD-OCT) system to generate a line-shaped imaging beam with almost uniform distribution of the optical power in the line direction. This design overcomes the severe sensitivity loss (∼10 dB) observed along the line length direction (B-scan) in LF-OCT systems based on cylindrical lens line generators. The PL-LF-SD-OCT system offers almost isotropic spatial resolution (Δx and Δy ∼2 µm, Δz ∼1.8 µm) in free space and sensitivity of ∼87 dB for 2.5 mW imaging power at 2,000 fps imaging rate with only ∼1.6 dB sensitivity loss along the line length. Images acquired with the PL-LF-SD-OCT system allow for visualization of the cellular and sub-cellular structure of biological tissues.

Modified algebraic reconstruction technique based on circular scanning geometry to improve processing time in photoacoustic tomography

AbstractPhotoacoustic imaging is low‐risk, and noninvasive tool for imaging biological tissues that acoustically respond to absorbed irradiating nonionized short laser pulse by tissue, then the image of light energy absorption distribution in the tissue has been reconstructed by image reconstruction algorithms. Indeed, photoacoustic tomography is a hybrid imaging modality that combines pure optical and acoustic imaging methods to take advantage of them, therefore, it contains high optical contrast with good ultrasonic resolution. However, improving its main parts is challenging. One of the most important parts of photoacoustic imaging is image reconstruction using appropriate algorithms. There are various image reconstruction methods. Image reconstruction based on an algebraic algorithm can reconstruct a clear image without artifact, but the algorithm is typically time‐consuming. This paper deals with this drawback of the algorithm. Simulations demonstrate significant improvement in the processing time of reconstructed images achieved by our proposed algorithm as compared to the phase‐controlled algorithm. Based on the image reconstruction algorithm in circular scanning geometry presented in this article, the processing time required to create a 2D tomographic image is reduced from 60 to 3.89 s compared to our previous work, which was based on a phase‐controlled algorithm. This improvement was based on inspiration from the experiences of our past works in dealing with various image reconstruction algorithms, which ultimately led to improvement in the calculation time.

Non-contact and label-free biomechanical imaging: Stimulated Brillouin microscopy and beyond.

Brillouin microscopy based on spontaneous Brillouin scattering has emerged as a unique elastography technique because of its merit of non-contact, label-free, and high-resolution mechanical imaging of biological cell and tissue. Recently, several new optical modalities based on stimulated Brillouin scattering have been developed for biomechanical research. As the scattering efficiency of the stimulated process is much higher than its counterpart in the spontaneous process, stimulated Brillouin-based methods have the potential to significantly improve the speed and spectral resolution of existing Brillouin microscopy. Here, we review the ongoing technological advancements of three methods, including continuous wave stimulated Brillouin microscopy, impulsive stimulated Brillouin microscopy, and laser-induced picosecond ultrasonics. We describe the physical principle, the representative instrumentation, and biological application of each method. We further discuss the current limitations as well as the challenges for translating these methods into a visible biomedical instrument for biophysics and mechanobiology.

A Telecom O-Band Emitter in Diamond.

Color centers in diamond are promising platforms for quantum technologies. Most color centers in diamond discovered thus far emit in the visible or near-infrared wavelength range, which are incompatible with long-distance fiber communication and unfavorable for imaging in biological tissues. Here, we report the experimental observation of a new color center that emits in the telecom O-band, which we observe in silicon-doped bulk single crystal diamonds and microdiamonds. Combining absorption and photoluminescence measurements, we identify a zero-phonon line at 1221 nm and phonon replicas separated by 42 meV. Using transient absorption spectroscopy, we measure an excited state lifetime of around 270 ps and observe a long-lived baseline that may arise from intersystem crossing to another spin manifold.

Magneto-Acoustic Imaging in Biology

This review examines the use of magneto-acoustic methods to measure electrical conductivity. It focuses on two techniques developed in the last two decades: Magneto-Acoustic Tomography with Magnetic Induction (MAT-MI) and Magneto-Acousto-Electrical Tomography (MAET). These developments have the potential to change the way medical doctors image biological tissue.

High-contrast interaction-free quantum imaging method

Quantum imaging techniques offer enhanced resolution, contrast, and precision at ultralow illumination levels compared to traditional imaging approaches. Relying on the unique properties of entangled photon pairs, two of these techniques stand out: the correlation-based quantum imaging technique provides visibility enhancement in imaging of a low-reflectivity object which is subject to excessive noise and losses, while the interaction-free ghost imaging allows for probing the presence of an object with an ultimately low number of photons. Here we propose a quantum imaging scheme that combines the unique advantages of these two approaches. We show that this scheme offers high-contrast imaging of objects with a minimal number of photons that can minimize thermal noise efficiently and create background-free images. We anticipate that this approach can find application in the imaging of photosensitive biological tissues in a noninvasive and harm-free fashion.

Microlenses Fabricated by Two‐Photon Laser Polymerization for Cell Imaging with Non‐Linear Excitation Microscopy

AbstractNon‐linear excitation microscopy offers several advantages for in‐vivo imaging compared to conventional confocal techniques. However, tissue penetration can still be an issue due to scattering and spherical aberrations induced on focused beams by the tissue. The use of low numerical aperture objectives to pass through the outer layers of the skin, together with high dioptric power microlenses implanted in‐vivo close to the observation volume, can be beneficial to the reduction of optical aberrations. Here, Fibroblast cell culture plano‐convex microlenses to be used for non‐linear imaging of biological tissue are developed and tested. The microlenses can be used as single lenses or multiplexed in an array. A thorough test of the lenses wavefront is reported together with the modulation transfer function and wavefront profile. Magnified fluorescence images can be retrieved through the microlenses coupled to commercial confocal and two‐photon excitation scanning microscopes. The signal‐to‐noise ratio of the images is not substantially affected by the use of the microlenses and the magnification can be adjusted by changing the relative position of the microlens array to the microscope objective and the immersion medium. These results are opening the way to the application of implanted micro‐optics for optical in‐vivo inspection of biological processes.

Development of Terahertz Imaging Markers for Pancreatic Ductal Adenocarcinoma using Maximum A Posteriori Probability (MAP) Estimation.

Pancreatic ductal adenocarcinoma (PDAC) is one of the significant reasons for cancer-related death in the United States due to a lack of timely prognosis and the poor efficacy of the standard treatment protocol. Immunotherapy-based neoadjuvant therapy, such as stereotactic body radiotherapy (SBRT), has shown promising results compared to conventional radiotherapy in strengthening the antitumor response in PDAC. To probe and quantify the antitumor response with SBRT, we propose to study the tumor microenvironment using terahertz time-domain spectroscopy (THz-TDS). Since the tumor's complex microenvironment plays a key role in disease progression and treatment supervision, THz-TDS can be a revolutionary tool to help in treatment planning by probing the changes in the tissue microenvironment. This paper presents THz-TDS of paraffin-embedded PDAC samples utilizing a clinically relevant genetically engineered mouse model. This Article aims to develop and validate a novel time-domain approximation method based on maximum a posteriori probability (MAP) estimation to extract terahertz parameters, namely, the refractive index and the absorption coefficient, from THz-TDS. Unlike the standard frequency-domain (FD) analysis, the parameters extracted from MAP construct better-conserved tissue parameters estimates, since the FD optimization often incorporates errors due to numerical instabilities during phase unwrapping, especially when propagating in lossy media. The THz-range index of refraction extracted from MAP and absorption coefficient parameters report a statistically significant distinction between PDAC tissue regions and their healthy equivalents. The coefficient of variation of the refractive index extracted by MAP is one order of magnitude lower compared to the one extracted from FD analysis. The index of refraction and absorption coefficient extracted from the MAP are suggested as the best imaging markers to reconstruct THz images of biological tissues to reflect their physical properties accurately and reproducibly. The obtained THz scans were validated using standard histopathology.

Virtual Fluorescence Translation for Biological Tissue by Conditional Generative Adversarial Network.

The online version contains supplementary material available at 10.1007/s43657-023-00094-1.

A Review on the Coupled Method of Using the Magnetic and Acoustic Fields for Biological Tissue Imaging

Magnetic field and acoustic field coupled imaging methods mainly include magnetoacoustic tomography, magneto-acousto-electrical tomography, and thermoacoustic tomography, all of which non-invasively achieve the electrical conductivity imaging of tissues with a resolution of up to the millimeter scale. The principles of these three imaging methods and the research progress in the last two decades are reviewed. First, the principles of the three magnetic and acoustic field coupled methods are individually introduced. The progress in medical electromagnetic imaging is further elaborated, and finally the future directions and summary of the coupled imaging methods are summarized.

Extreme Bottom-up Gold Filling of High Aspect Ratio Features.

ConspectusWhere copper interconnects fabricated using superconformal electrodeposition processes have enabled dramatic advances in microelectronics over the past quarter century, gold filled gratings fabricated using superconformal Bi3+-mediated bottom-up filling electrodeposition processes promise to enable a new generation of X-ray imaging and microsystem technologies. Indeed, bottom-up Au-filled gratings have demonstrated excellent performance in X-ray phase contrast imaging of biological soft tissue and other low Z element samples even as studies using gratings with inferior Au fill have captured the potential for broader biomedical application. Four years ago, the Bi-stimulated bottom-up Au electrodeposition process was a scientific novelty where gold deposition was localized entirely on the bottoms of metallized trenches 3-μm-deep and 2-μm-wide, an aspect ratio of only 1.5, on centimeter scale fragments of patterned silicon wafers. Today the room-temperature processes routinely yield uniformly void-free filling of metallized trenches 60-μm-deep and 1-μm-wide, an aspect ratio 60, in gratings patterned across 100 mm Si wafers. Four distinctive characteristics of the evolution of void-free filling in the Bi3+-containing electrolyte are seen in experimental Au filling of fully metallized recessed features such as trenches and vias: (1) an "incubation period" of conformal deposition, (2) subsequent Bi-activated deposition localized on the bottom surface of features, (3) sustained bottom-up deposition that yields void-free filling, and (4) self-passivation of the active growth front at a distance from the feature opening defined by operating conditions. A recent model captures and explains all four features. The electrolyte solutions are simple and nontoxic, being near-neutral pH and composed of Na3Au(SO3)2 + Na2SO3 containing micromolar concentrations of Bi3+ additive, the latter generally introduced through electrodissolution from the metal. The influences of additive concentration, metal ion concentration, electrolyte pH, convection, and applied potential have been examined in some depth using both electroanalytical measurements on planar rotating disk electrodes and studies of feature filling, thereby defining and elucidating relatively wide processing windows for defect-free filling. The process control for bottom-up Au filling processes is observed to be quite flexible, with online changes of potential as well as concentration and pH adjustments during the course of filling compatible with processing. Furthermore, monitoring has enabled optimization of the filling evolution, including to shorten the incubation period for accelerated filling and to fill features of ever higher aspect ratio. The results to date indicate that the demonstrated filling of trenches with an aspect ratio of 60 represents a lower bound, a value determined only by the features presently available.

Comparison of Fabrication Methods for Fiber‐Optic Ultrasound Transmitters Using Candle‐Soot Nanoparticles

AbstractCandle‐soot nanoparticles (CSNPs) have shown great promise for fabricating optical ultrasound (OpUS) transmitters. They have a facile, inexpensive synthesis whilst their unique, porous structure enables a fast heat diffusion rate which aids high‐frequency ultrasound generation necessary for high‐resolution clinical imaging. These composites have demonstrated high ultrasound generation performance showing clinically relevant detail, when applied as macroscale OpUS transmitters comprising both concave and planar surfaces, however, less research has been invested into the translation of this material's technology to fabricate fiber‐optic transmitters for image guidance of minimally invasive interventions. Here, are reported two fabrication methods of nanocomposites composed of CSNPs embedded within polydimethylsiloxane (PDMS) deposited onto fiber‐optic end‐faces using two different optimized fabrication methods: “All‐in‐One” and “Direct Deposition.” Both types of nanocomposite exhibit a smooth, black domed structure with a maximum dome thickness of 50 µm, broadband optical absorption (>98% between 500 and 1400 nm) and both nanocomposites generated high peak‐to‐peak ultrasound pressures (>3 MPa) and wide bandwidths (>29 MHz). Further, high‐resolution (<40 µm axial resolution) B‐mode ultrasound imaging of ex vivo lamb brain tissue demonstrating how CSNP‐PDMS OpUS transmitters can allow for high fidelity minimally invasive imaging of biological tissues is demonstrated.

Optical design and fabrication of zinc selenide microlens array with extended depth of focus for biomedical imaging

Optical coherence tomography is a well-known technique for the optical imaging biological tissues. However, the depth scanning range of high-resolution optical coherence tomography is restricted by its depth of focus. In this study, a Zinc Selenide (ZnSe) Microlens Array (MLA) is employed to overcome the depth-of-focus limitation of optical coherence tomography. The ZnSe material with a low Abbe number and high chromatic dispersion extends the depth of focus with transverse resolution. The ZnSe MLA focused the incident light (from visible to near-infrared (NIR) region) on multiple focal planes with the uniform distribution of light over a biological tissue. The MLA is designed using Zemax OpticStudio software and fabricated via a single-point diamond-turning based on Slow Tool Servo (STS) configuration. STS machining has the unique advantage of offering larger degrees of freedom with no additional baggage, thereby reducing the setup time. The experimental results show the effectiveness of the STS machining process in fabricating ZnSe MLA with desired accuracies. The characterization of fabricated MLA using Coherence Correlation Interferometry (CCI) depicts uniform lenslets with no structural and positional distortion, with a total error of 32 nm within the tolerance limit.

Intraoperative Assessment of Surgical Margins in Cancer Resection Surgery Via the Sub-Diffuse Optical Tomography "S-DOT"

In Head and Neck Squamous Cell Carcinomas (HNSCC), positive margins after surgical resection dominate the clinical outcome of patients. Between 15-30 precent of all HNSCC surgeries result in a positive margin (>5mm) that requires postoperative chemo-radiation, radiotherapy, and/or revision surgeries. To minimize local recurrence, margin assessment is typically performed through surgical pathology departments; however, this technique often takes more than 24 hours to process and only a small fraction of the total surgical margin is evaluated. A second, intraoperativeapproach used by surgeons to minimize local recurrence is frozen section analysis (FSA), which in time intensive and suffers heavily from sampling errors. To effect change, we have hypothesized a sub-diffuse optical tomography modality that can identify the differences in depth sensitivity of the fluorescence, Cetuximab-IRDye800CW conjugate (ICON), by the fluorescent photons collected from sub-diffused media as a function of the photon exit angle from the excited tissue. Based on promising preliminary simulations using Monte Carlo MATLAB, closed vs. open aperture fluorescence imaging in biological tissue demonstrated an enhanced true depth of fluorescence resolution up to 6mm, well beyond the insufficient 5mm mark. By identifying the deep margins from the fluorescent peaks within 5 minutes, we hope to improve complete oncological surgery by providing surgeons an exact region of interest on the specimen where the tumor is closest to the edge, so they may continue surgery by providing sugeons an exact region of interest on the specimen where the tumor is closest to the edge, so they may continue surgery on the spot to minimize the probability of cancer being left behind.

Prospects on ultrasound measurement techniques with optical fibers

Ultrasound sensors have been widely used in medical imaging, as well as structural health monitoring (SHM) and non-destructive testing (NDT) in civil and mechanical structures. Covering entire structures and imaging large areas requires multiplexing of many ultrasound sensors with single readout instrument, which can be difficult for traditional piezoelectric transducers. Optical fiber-based sensors offer numerous advantages such as being lightweight, small, the ability to be embedded, immunity to electro-magnetic interference, and the ability to be multiplexed and distributed ultrasound sensors. Fiber ultrasound sensors are regarded as an ideal sensing solution for SHM and NDT, and even most recently for medical imaging due to its broadband ultrasound response and distributed capability. Micro and nanofibers are made smaller than telecom fibers using a wider selection of sensing materials with higher bending capability, which makes them ideal for high frequency (hundreds of MHz) ultrasound detection of micrometer cracks and imaging biological tissues. New optical materials and fabrication techniques are shaping the future with exceptionally small ultrasound sensors and actuators, extending the range of applications in SHM, NDT and medical imaging with higher accuracy and better precision over larger areas.