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In this study, we demonstrate the potential of the bornite crystal structure (Cu5FeS4) of copper iron sulfide as a second near infrared (NIR-II) photoacoustic (PA) contrast agent. Bornite exhibits comparable dose-dependent biocompatibility to copper sulfide nanoparticles in a cell viability study with HepG2 cells, while exhibiting a 10-fold increase in PA amplitude. In comparison to other benchmark contrast agents at similar mass concentrations, bornite demonstrated a 10× increase in PA amplitude compared to indocyanine green (ICG) and a 5× increase compared to gold nanorods (AuNRs). PA signal was detectable with a light pathlength greater than 5 cm in porcine tissue phantoms at bornite concentrations where in vitro cell viability was maintained. In vivo imaging of mice vasculature resulted in a 2× increase in PA amplitude compared to AuNRs. In summary, bornite is a promising NIR-II contrast agent for deep tissue PA imaging.

Since the advent of confocal microscopy, advances in tissue clearing have allowed researchers to push the limits of imaging depth and dive deeper into the precise 3D structures of biological specimens. As clearing methods are discovered, refined, and retired, it behooves the prudent microscopist to consider the pros and cons of various tissue clearing methods and systematically evaluate whether tissue clearing is beneficial to answer their research questions. Herein, I will briefly discuss the evolution of tissue clearing, pros and cons of more popular methods and techniques related to fluorescence microscopy, and key considerations for selecting a method most likely to yield experimental success. [ABSTRACT FROM AUTHOR]

The concept of a "smoke ring" in electromagnetic fields can be used to describe the spatial distribution and diffusion of electromagnetic fields with either frequency or time. This provides an intuitive basis for the qualitative interpretation of artificial-source electromagnetic measurement results. The existing discussions regarding this field of study have mainly focused on the smoke rings of a magnetic dipole or loop source. In the present work, smoke rings of other commonly used grounded-wire sources in the time domain are investigated. The results show that the smoke ring of grounded-wire sources is more complex than that of magnetic sources. A grounded-wire source can generate an induced current in both horizontal and vertical directions. The horizontal induced current includes positive and negative parts. Both parts of the horizontal induced current maximum diffuse downward perpendicular to the surface, but the diffusion velocity of the negative part is faster, approximately 5.6 times that of the positive part. The vertical induced current maximum diffuses at 45° from the grounded surface with a velocity approximately 5 times that of the positive horizontal induced current. The smoke ring of the horizontal induced current closely resembles a basin, while that of the vertical induced current is more similar to two separate cylinders. Finally, the imaging depth based on horizontal and vertical induced currents is obtained by the statistical relationship between the induced current maximums and the diffusion depth, which are equal to 1.4 times and 1.25 times the diffusion depth, respectively. [ABSTRACT FROM AUTHOR]

Vision is essential in the diagnostic capabilities in the speciality of dermatology. However, humans are limited in colour vision by the trichromatic visual system that we possess. Multispectral and hyperspectral imaging can overcome this limitation and non‐invasively provide novel information about a skin lesion at the cellular level. A literature review from January 2019 to March 2021 for hyperspectral and multispectral imaging in the field of dermatology was conducted. Multispectral/Hyperspectral imaging continues to generate significant research and interest in dermatology. Much of this research is on distinguishing melanoma from benign nevi as this could allow for a diagnosis without biopsy. In addition, adding multispectral/hyperspectral imaging to smartphones is being researched in order to create a portable and low‐cost device that can be used in remote areas. One of the limitations in developing devices utilizing hyperspectral imaging has been a sacrifice in specificity in order to maximize sensitivity. Potential solutions to combat this that are being researched include combining multispectral/hyperspectral imaging with other imaging modalities such as photoacoustic imaging in order to overcome the limitations of using each individually. Multispectral/Hyperspectral imaging could be an instrumental aid for clinicians in examining, diagnosing and developing the management plan for patient's skin lesions. [ABSTRACT FROM AUTHOR]

Connective tissues in vertebrates consist of many anisotropic structures formed by collagen and muscle fibers, which could also generate intense second harmonic (SH). In SHG based tissue imaging, the incident light, when subjected to birefringence and scattering, would lead to a rapid decrement in imaging depth. The work simulating polarized light propagating through a thick and highly-scattering semi-infinite medium using a polarization-sensitive Monte Carlo model find that circular polarization would achieve deeper penetration depth. Henceforth, we use polarization engineered SHG imaging to investigate fish scales and pig tendon/dermis of various thickness, as well as the corresponding depolarization effect as a function of the imaging depth in this work. Critically, we have verified quantitatively the previous simulation results and presented the possibility to greatly improve the imaging of thick anisotropic and scattering tissues through engineering polarization. In parallel to wavefront shaping that uses a spatial light modulator or a wavefront sensor based deformable mirror to increase the signal-to-background (SBR) ratio in imaging, our approach is simple, effective, and sensitive to tissue anisotropy.

Pulsed laser diodes (PLDs) promise to be an attractive alternative to solid-state laser sources in photoacoustic tomography (PAT) due to their portability, high-pulse repetition frequency (PRF), and cost effectiveness. However, due to their lower energy per pulse, which, in turn, results in lower fluence required per photoacoustic signal generation, PLD-based photoacoustic systems generally have maximum imaging depth that is lower in comparison to solid-state lasers. Averaging of multiple frames is usually employed as a common practice in high PRF PLD systems to improve the signal-to-noise ratio of the PAT images. In this work, we demonstrate that by combining the recently described approach of subpitch translation on the receive-side ultrasound transducer alongside averaging of multiple frames, it is feasible to increase the depth sensitivity in a PLD-based PAT imaging system. Here, experiments on phantom containing diluted India ink targets were performed at two different laser energy level settings, that is, 21 and $27~\mu \text{J}$. Results obtained showed that the imaging depth improves by ~38.5% from 9.1 to 12.6 mm for 21- $\mu \text{J}$ energy level setting and by ~33.3% from 10.8 to 14.4 mm for 27- $\mu \text{J}$ energy level setting by using $\lambda $ /4-pitch translation and average of 128 frames in comparison to $\lambda $ -pitch data acquired with the average of 128 frames. However, the achievable frame rate is reduced by a factor of 2 and 4 for $\lambda $ /2 and $\lambda $ /4 subpitch translation, respectively. [ABSTRACT FROM AUTHOR]

The depth of two-photon fluorescence imaging in turbid media can be significantly enhanced by the use of the here described fluorescence detection method that allows to efficiently collect scattered fluorescence photons from a wide area of the turbid sample. By using this detector we were able to perform imaging of turbid samples, simulating brain tissue, at depths up to 3 mm, where the two-photon induced fluorescence signal is too weak to be detected by means used in conventional two-photon microscopy.

A considerable amount of early breast tumors grown at a depth over 2 cm in breast tissues. With high near-infrared absorption of iron-platinum (FePt) nanoparticles, we achieved few centimeters deep photoacoustic (PA) imaging for the diagnosis of breast tumors. The imaging depth can extend over 5 cm in chicken breast tissues at the low laser energy density of 20 mJ/cm2 (≤ ANSI safety limit). After anti-VEGFR conjugation and the tail-vein injection, we validated their targeting on tumor sites by the confocal microscopy and PA imaging. Using a home-made whole-body in vivo PA imaging, we found that the nanoparticles were rapidly cleared away from the site of the tumor and majorly metabolized through the liver. These results validated the clinical potential of the FePt nanoparticles in the low-toxicity PA theragnosis of early breast cancer and showed the capacity of our whole-body PA imaging technique on monitoring the dynamic biodistribution of nanoparticles in the living body.

The effect of optical cleaning method combined with laser speckle imaging (LSI) was discussed to improve the detection depth of LSI due to high scattering characteristics of skin, which limit its clinical application. A double-layer skin tissue model embedded with a single blood vessel was established, and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent. 808nm semiconductor and 632.8nm He–Ne lasers were selected to study the effect of optical clearing agents (OCAs) on photon deposition in tissues. Results show that the photon energy deposition density in the epidermis increases with the amount of tissue fluid replaced by OCA. Compared with glucose solution, polyethylene glycol 400 (PEG 400) and glycerol can considerably increase the average penetration depth of photons in the skin tissue, thereby raising the sampling depth of the LSI. After the action of glycerol, PEG 400, and glucose, the average photon penetration depth is increased by 51.78%, 51.06%, and 21.51% for 808nm, 68.93%, 67.94%, and 26.67% for 632.8 nm lasers, respectively. In vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood flow rate, whereas PEG 400 can significantly improve the capability of light penetration without affecting blood velocity, which exhibits considerable potential in the monitoring of blood flow in skin tissues.

Featured Application: SD-OCT imaging depth enhancement with improved contrast. We designed and fabricated a telecentric f-theta imaging lens (TFL) to improve the imaging performance of spectral domain optical coherence tomography (SD-OCT). By tailoring the field curvature aberration of the TFL, the flattened focal surface was well matched to the detector plane. Simulation results showed that the spot in the focal plane fitted well within a single pixel and the modulation transfer function at high spatial frequencies showed higher values compared with those of an achromatic doublet imaging lens, which are commonly used in SD-OCT spectrometers. The spectrometer using the TFL had an axial resolution of 7.8 μm, which was similar to the theoretical value of 6.2 μm. The spectrometer was constructed so that the achromatic doublet lens was replaced by the TFL. As a result, the SD-OCT imaging depth was improved by 13% (1.85 mm) on a 10 dB basis in the roll-off curve and showed better sensitivity at the same depth. The SD-OCT images of a multi-layered tape and a human palm proved that the TFL was able to achieve deeper imaging depth and better contrast. This feature was seen very clearly in the depth profile of the image. SD-OCT imaging performance can be improved simply by changing the spectrometer's imaging lens. By optimizing the imaging lens, deeper SD-OCT imaging can be achieved with improved sensitivity. [ABSTRACT FROM AUTHOR]

The effect of optical cleaning method combined with laser speckle imaging (LSI) was discussed to improve the detection depth of LSI due to high scattering characteristics of skin, which limit its clinical application. A double-layer skin tissue model embedded with a single blood vessel was established, and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent. 808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the effect of optical clearing agents (OCAs) on photon deposition in tissues. Results show that the photon energy deposition density in the epidermis increases with the amount of tissue fluid replaced by OCA. Compared with glucose solution, polyethylene glycol 400 (PEG 400) and glycerol can considerably increase the average penetration depth of photons in the skin tissue, thereby raising the sampling depth of the LSI. After the action of glycerol, PEG 400, and glucose, the average photon penetration depth is increased by 51.78%, 51.06%, and 21.51% for 808nm, 68.93%, 67.94%, and 26.67% for 632.8 nm lasers, respectively. In vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood flow rate, whereas PEG 400 can significantly improve the capability of light penetration without affecting blood velocity, which exhibits considerable potential in the monitoring of blood flow in skin tissues. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging (PAI) provides high-resolution and high-optical-contrast imaging beyond optical diffusion limit. Further improvement in imaging depth has been achieved by using near-infrared window-I (NIR-I, 700 to 900 nm) for illumination, due to lower scattering and absorption by tissues in this wavelength range. Recently, near-infrared window-II (NIR-II, 900 to 1700 nm) has been explored for PAI. We studied the imaging depths in biological tissues for different illumination wavelengths in visible, NIR-I, and NIR-II regions using Monte Carlo (MC) simulations and validated with experimental results. MC simulations were done to compute fluence in tissue, absorbance in blood vessel, and in a spherical absorber (mimicking sentinel lymph node) embedded at different depths in breast tissue. Photoacoustic tomography and acoustic resolution photoacoustic microscopy experiments were conducted to validate the MC results. We demonstrate that maximum imaging depth is achieved by wavelengths in NIR-I window (~800 nm) when the energy density deposited is same for all wavelengths. However, illumination using wavelengths around 1064 nm (NIR-II window) gives the maximum imaging depth when the energy density deposited is proportional to maximum permissible exposure (MPE) at corresponding wavelength. These results show that it is the higher MPE of NIR-II window that helps in increasing the PAI depth for chromophores embedded in breast tissue. [ABSTRACT FROM AUTHOR]

Broadband two-photon fluorescence (TPF) imaging system based on femtosecond oscillator is built. Broadband TPF signal generated from Rhodamine B molecule is detected at different detection windows. Both TPF signals detected at short wavelength detection window of 545–615 nm and long wavelength detection window of 642–708 nm are used for TPF imaging. Through switching detection window from short wavelength to long wavelength, deepened imaging depth is achieved. The TPF imaging results, with single 9 0 0 × 9 0 0 pixels frame taking time of 4–8 s, demonstrate high performance and the good reliability of the imaging system. [ABSTRACT FROM AUTHOR]

Summary: White‐light microsphere‐assisted microscopy is a full‐field and label‐free imaging promising technique making it possible to achieve a subdiffraction lateral resolution. However, performance of this technique depends not only on the geometrical parameters but also on the illumination conditions of the optical system. In the present work, experimental measurements and computer simulations have been performed in air in order to determine the influence of the two diaphragm apertures of the Köhler arrangement and the spectral width of the light source on both the depth‐of‐focus of the microsphere and the optimization of the imaging contrast. Furthermore, the super‐resolution phenomenon is demonstrated and the cumulated optical aberrations are shown through the measurement of the optical transfer function for the different arrangements of the illumination part. [ABSTRACT FROM AUTHOR]

We designed and fabricated a telecentric f-theta imaging lens (TFL) to improve the imaging performance of spectral domain optical coherence tomography (SD-OCT). By tailoring the field curvature aberration of the TFL, the flattened focal surface was well matched to the detector plane. Simulation results showed that the spot in the focal plane fitted well within a single pixel and the modulation transfer function at high spatial frequencies showed higher values compared with those of an achromatic doublet imaging lens, which are commonly used in SD-OCT spectrometers. The spectrometer using the TFL had an axial resolution of 7.8 μm, which was similar to the theoretical value of 6.2 μm. The spectrometer was constructed so that the achromatic doublet lens was replaced by the TFL. As a result, the SD-OCT imaging depth was improved by 13% (1.85 mm) on a 10 dB basis in the roll-off curve and showed better sensitivity at the same depth. The SD-OCT images of a multi-layered tape and a human palm proved that the TFL was able to achieve deeper imaging depth and better contrast. This feature was seen very clearly in the depth profile of the image. SD-OCT imaging performance can be improved simply by changing the spectrometer’s imaging lens. By optimizing the imaging lens, deeper SD-OCT imaging can be achieved with improved sensitivity.

We established a photoacoustic imaging (PAI) system that can provide variable gain at different depths. The PAI system consists of a pulsed laser with an optical parametric oscillator working at a 728nm wavelength and an imaging-acquisition-and-processing unit with an ultrasound transducer. A voltage-controlled attenuator was used to realize variable gain at different depths when acquiring PAI signals. The proof-of-concept imaging results for variable gain at different depths were achieved using specific phantoms. Both resolution and optical contrast obtained through the results of variable gain for a targeted depth range are better than those of constant gain for all depths. To further testify the function, we imaged the sagittal section of the body of in vivo nude mice. In addition, we imaged an absorption sample embedded in a chicken breast tissue, reaching a maximum imaging depth of ∼4.6cm. The results obtained using the proposed method showed better resolution and contrast than when using 50dB gain for all depths. The depth range resolution was ∼1mm, and the maximum imaging depth of our system reached ∼4.6cm. Furthermore, blood vessels can be revealed and targeted depth range can be selected in nude mice imaging.

Influence of acoustic inhomogeneities and resulting reflection artifacts is an important problem in reflection-mode photoacoustic imaging. Absorption of light by skin and superficial optical absorbers will generate photoacoustic transients, which traverse into the tissue and get reflected from structures having different acoustic impedance. These reflected photoacoustic signals, when reconstructed, may appear in the region of interest, which causes difficulties in image interpretation. We propose a novel method to identify and potentially eliminate reflection artifacts in photoacoustic images using photoacoustic-guided focused ultrasound [PAFUSion]. Our method uses focused ultrasound pulses to mimic the wave field produced by photoacoustic sources and thus provides a way to identify reflection artifacts in clinical combined photoacoustic and pulse-echo ultrasound. Simulation and phantom results are presented to demonstrate the validity and impact of this method. Results show that PAFUSion can identify reflections in photoacoustic images and thus envisages potential for improving photoacoustic imaging of acoustically inhomogeneous tissue.

We established a photoacoustic imaging (PAI) system that can provide variable gain at different depths. The PAI system consists of a pulsed laser with an optical parametric oscillator working at a 728 nm wavelength and an imaging-acquisition-and-processing unit with an ultrasound transducer. A voltage-controlled attenuator was used to realize variable gain at different depths when acquiring PAI signals. The proof-of-concept imaging results for variable gain at different depths were achieved using specific phantoms. Both resolution and optical contrast obtained through the results of variable gain for a targeted depth range are better than those of constant gain for all depths. To further testify the function, we imaged the sagittal section of the body of in vivo nude mice. In addition, we imaged an absorption sample embedded in a chicken breast tissue, reaching a maximum imaging depth of ∼ 4.6 cm. The results obtained using the proposed method showed better resolution and contrast than when using 50 dB gain for all depths. The depth range resolution was ∼ 1 mm, and the maximum imaging depth of our system reached ∼ 4.6 cm. Furthermore, blood vessels can be revealed and targeted depth range can be selected in nude mice imaging. [ABSTRACT FROM AUTHOR]

Dual-channel spectral domain optical coherence tomography (SD-OCT) is one of the effective methods for improving imaging depth and imaging speed. In this paper, we design a dual-channel SD-OCT system based on a single spectrometer that can operate in two modes: (1) Increasing imaging speed and (2) expanding imaging depth. An optical path offset is preintroduced between the two channels to separate the two-channel data. However, this offset increases the requirement for the spectral resolution of the spectrometer in mode (1), so compressive sensing (CS) technology is used herein to overcome this problem. Consequently, in mode (1), when the spectral resolution of the spectrometer is the same as that used in the single-channel system, we use a dual-channel SD-OCT system combined with CS technology to double the imaging speed. In mode (2), when the spectral resolution of the spectrometer is only half of that used in a single-channel system, the imaging depth can be nearly doubled. We demonstrate the feasibility and effectiveness of the method proposed in this work by imaging a mirror, a fish fin, a fish eye, and an onion.

In vivo tissue transparency in the visible light spectrum is beneficial for many research applications that use optical methods, whether it involves in vivo optical imaging of cells or their activity, or optical intervention to affect cells or their activity deep inside tissues, such as brain tissue. The classical view is that a tissue is transparent if it neither absorbs nor scatters light, and thus absorption and scattering are the key elements to be controlled to reach the necessary transparency. This review focuses on the latest genetic and chemical approaches for the decoloration of tissue pigments to reduce visible light absorption and the methods to reduce scattering in live tissues. We also discuss the possible molecules involved in transparency.

To advance the practical application of optical coherence tomography (OCT) in the field of biomedical imaging, the imaging depth must be extended without sacrificing resolution while maintaining sufficient sensitivity. However, there is an inherent trade-off between lateral resolution and depth of field (DOF) in OCT. To address this shortcoming, this article proposes a multifocal Bessel beam spectral-domain optical coherence tomography (MBSDOCT) capable of increasing the DOF with unchanged lateral resolution and a high signal-tonoise ratio. The proposed technique is demonstrated by simulation and experiment. A three-focal MBSDOCT with an axicon lens theoretically achieved a DOF of ∼6 mm with a lateral resolution of ∼13 μm. In imaging experiments performed on the acinar cells of orange tissue, a measured DOF of ∼4 mm was demonstrated with a sensitivity penalty of ∼18.1 dB, relative to the Gaussian beam spectral-domain OCT, with a 9-mW light source. [ABSTRACT FROM AUTHOR]

• A novel strategy is presented to enhance the image contrast/SNR in SHG-LSM using the first-order modulation (1 M) of SHG signals in the frequency domain. • A down-conversion circuit is developed to extract useful yet hidden information from higher-order harmonics. • With a better signal SNR obtained from 1 M signals, the contrast of SHG images is enhanced by a factor of 2.18, while the scanning speed is increased by a factor of 2.5 compared to the images taken conventionally without signal modulation. • The proposed method is simple, highly flexible, cost-effective, and easy to implement in a standard laser scanning microscope since it does not require a lock-in amplifier and complex optical elements, ultimately facilitating high-quality, high-speed, and deep penetration SHG imaging. The contrast or signal-to-noise ratio (SNR) in images is a crucial parameter that determines the quality of images in second harmonic generation laser scanning microscopy (SHG-LSM). With a better image contrast/SNR, SHG-LSM can be performed at a faster frame rate or deeper tissue locations without compromising image quality. In this work, we present a novel strategy based on the SHG signals of first-order modulation (1 M) to enhance the image contrast/SNR. Notably, a photodetector (i.e., photomultiplier tube) has a better signal SNR during the photon-to-electron conversion process at the frequency of 1 M, which is equivalent to the laser pulse repetition frequency. The improved signal SNR thus enhances the image quality, which agrees well with the results of the measured electrical spectra. A remarkable increment of image contrast by more than a factor of two has been obtained in images by using 1 M. In addition, the image acquisition time is also shortened by a factor of 2.5 compared to that for acquiring images with similar contrast taken without signal modulation. Furthermore, by analyzing the dependencies of image contrast/SNR on sample depth, we demonstrate that the images obtained with 1 M have better quality than those obtained without signal modulation at the same imaging depth. [ABSTRACT FROM AUTHOR]

Three-dimensional optical super-resolution imaging is capable of providing 3D visualization of cellular structures in nanoscale detail. The past decade has witnessed the blossoming of 3D super-resolution imaging technologies. In this review, we comprehensively discuss and compare the imaging depth, resolution enhancement, and imaging speed of the existing 3D super-resolution imaging techniques. [ABSTRACT FROM AUTHOR]

The developed optical clearing methods show great potential for imaging of large-volume tissues, but these methods present some nonnegligible limitations such as complexity of implementation and long incubation times. In this study, we tried to screen out rapid optical clearing agents by means of molecular dynamical simulation and experimental demonstration. According to the optical clearing potential of sugar and sugar-alcohol, we further evaluated the improvement in the optical clearing efficacy of mouse brain samples, imaging depth, fluorescence preservation, and linear deformation. The results showed that drops of sorbitol, sucrose, and fructose could quickly make the mouse brain sample transparent within 1 to 2 min, and induce about threefold enhancement in imaging depth. The former two could evidently enhance the fluorescence intensity of green fluorescent protein (GFP) and prodium iodide (PI) nuclear dye. Fructose could significantly increase the fluorescence intensity of PI, but slightly decrease the fluorescence intensity of GFP. Even though the three agents caused some shrinkage in samples, the contraction in horizontal and longitudinal directions are almost the same. [ABSTRACT FROM AUTHOR]

The signal-to-noise ratio (SNR) and imaging depth of photoacoustic (PA) imaging remain limited for clinical applications. The temperature can influence PA signals; the SNR of PA signals can be increased at higher temperatures. Therefore, the imaging quality and depth can be improved by the assistance of heating. Experimental results showed that the maximum imaging depth can be doubled by raising the temperature of the absorbers ( ex-vivo beef muscle) uniformly from $$20~^{\circ }\hbox {C}$$ to $$41~^{\circ }\hbox {C}$$ , and the SNR can be increased $$53 \,\%\, \mathrm{from}\, 20~^{\circ }\hbox {C}\, \mathrm{to}\, 45~^{\circ }\hbox {C}$$ . [ABSTRACT FROM AUTHOR]

Abstract: Multiphoton microscopy has enabled biologists to collect high-resolution images hundreds of microns into biological tissues, including tissues of living animals. While the depth of imaging exceeds that possible from any other form of light microscopy, multiphoton microscopy is nonetheless generally limited to depths of less than a millimeter. Many of the advantages of multiphoton microscopy for deep tissue imaging accrue from the unique nature of multiphoton fluorescence excitation. However, the quadratic relationship between illumination level and fluorescence excitation makes multiphoton microscopy especially susceptible to factors that degrade the illumination focus. Here we examine the effect of spherical aberration on multiphoton microscopy in fixed kidney tissues and in the kidneys of living animals. We find that spherical aberration, as evaluated from axial asymmetry in the point-spread function, can be corrected by adjustment of the correction collar of a water immersion objective lens. Introducing a compensatory positive spherical aberration into the imaging system decreases the depth-dependence of signal levels in images collected from living animals, increasing signal by up to 50%. [Copyright &y& Elsevier]

Optical coherence tomography (OCT) is a new modality capable of cross sectional imaging of biological tissue. Due to its many technical advantages such as high image resolution, fast acquisition time, and noninvasive capabilities, OCT is potentially useful in various medical applications. Because OCT systems can function with a fiber optic probe, they are applicable to almost any anatomic structures accessible either directly, or by endoscopy. OCT has the potential to provide a fast and noninvasive means for early clinical detection, diagnosis, screening, and monitoring of precancer and cancer. With an imaging depth range of 2-3 mm, OCT diagnostics are particularly suitable for the oral mucosa. Currently, it is difficult to detect premalignant and malignant oral lesions due to their often multifocal nature and need for repeated biopsies. The goal of this study was to evaluate the feasibility of OCT for the diagnosis of multiple stages of oral cancer progression. In this paper, we present not only conventional 2-D OCT images, but also 3-D volume images of normal and precancerous lesions. Our results demonstrate that OCT is a potential tool for cancer detection with comprehensive diagnostic images. [ABSTRACT FROM PUBLISHER]

• We make quantitative comparisons among the degree of polarizations of linear polarized light (LPL), elliptically polarized light (EPL), and circularly polarized light (CPL), as well as the various imaging depths using polarization engineered SHG on multiple anisotropic scattering tissues of various thicknesses. • CPL is proven to suffer less depolarization effect, enabling it to maintain a relatively longer penetration depth. • CPL (LPL) provides the possibility for the tissues with high (less) scattering and high anisotropic structures to obtain an improved imaging depth. Connective tissues in vertebrates consist of many anisotropic structures formed by collagen and muscle fibers, which could also generate intense second harmonic (SH). In SHG based tissue imaging, the incident light, when subjected to birefringence and scattering, would lead to a rapid decrement in imaging depth. The work simulating polarized light propagating through a thick and highly-scattering semi-infinite medium using a polarization-sensitive Monte Carlo model find that circular polarization would achieve deeper penetration depth. Henceforth, we use polarization engineered SHG imaging to investigate fish scales and pig tendon/dermis of various thickness, as well as the corresponding depolarization effect as a function of the imaging depth in this work. Critically, we have verified quantitatively the previous simulation results and presented the possibility to greatly improve the imaging of thick anisotropic and scattering tissues through engineering polarization. In parallel to wavefront shaping that uses a spatial light modulator or a wavefront sensor based deformable mirror to increase the signal-to-background (SBR) ratio in imaging, our approach is simple, effective, and sensitive to tissue anisotropy. [ABSTRACT FROM AUTHOR]

Our previous studies demonstrated the ultrasound-induced skin optical clearing enhancement with topical application of optical clearing agents on in vitro porcine skin and in vivo human skin. The objective of this study was to develop more effective methods by simultaneously using two kinds of skin permeation enhancers. The effect of ultrasound (SP) in combination with a chemical enhancer, sodium lauryl sulfate (SLS), on skin optical clearing was investigated. Light transmittance and imaging depth of in vitro porcine skin were measured with spectroscopy and optical coherence tomography (OCT). Three treatments were performed: 1) 60% glycerol (60% Gly); 2) 60% glycerol +15-min SP (Gly/SP); and 3) 60% glycerol + 1% SLS + 15-min SP (Gly/SLS/SP). We find that Gly/SLS/SP exhibits a most significant effect in increasing total transmittance and OCT imaging depth. Total transmittance increases by a factor of 1.9 (1276-nm light) to 3.4 (470-nm light) after 60 min. In addition, the effect after 30 min of Gly/SLS/SP exposure is almost the same as that after 60 min of Gly/SP exposure. Simultaneously, Gly/SLS/SP results in a 56% increase in OCT 1/e light penetration depth after 60 min, much better than 60% glycerol and Gly/SP. [ABSTRACT FROM PUBLISHER]

Dual-channel spectral domain optical coherence tomography (SD-OCT) is one of the effective methods for improving imaging depth and imaging speed. In this paper, we design a dual-channel SD-OCT system based on a single spectrometer that can operate in two modes: (1) Increasing imaging speed and (2) expanding imaging depth. An optical path offset is preintroduced between the two channels to separate the two-channel data. However, this offset increases the requirement for the spectral resolution of the spectrometer in mode (1), so compressive sensing (CS) technology is used herein to overcome this problem. Consequently, in mode (1), when the spectral resolution of the spectrometer is the same as that used in the single-channel system, we use a dual-channel SD-OCT system combined with CS technology to double the imaging speed. In mode (2), when the spectral resolution of the spectrometer is only half of that used in a single-channel system, the imaging depth can be nearly doubled. We demonstrate the feasibility and effectiveness of the method proposed in this work by imaging a mirror, a fish fin, a fish eye, and an onion. [ABSTRACT FROM AUTHOR]

In vivo tissue transparency in the visible light spectrum is beneficial for many research applications that use optical methods, whether it involves in vivo optical imaging of cells or their activity, or optical intervention to affect cells or their activity deep inside tissues, such as brain tissue. The classical view is that a tissue is transparent if it neither absorbs nor scatters light, and thus absorption and scattering are the key elements to be controlled to reach the necessary transparency. This review focuses on the latest genetic and chemical approaches for the decoloration of tissue pigments to reduce visible light absorption and the methods to reduce scattering in live tissues. We also discuss the possible molecules involved in transparency. [ABSTRACT FROM AUTHOR]