Biotissue Imaging Research Articles

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a “kill two birds with one stone” strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+–Zr4+] for [Y3+–Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+–Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with “burning after reading” was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Temporal focusing multiphoton microscopy with cross-modality multi-stage 3D U-Net for fast and clear bioimaging.

Temporal focusing multiphoton excitation microscopy (TFMPEM) enables fast widefield biotissue imaging with optical sectioning. However, under widefield illumination, the imaging performance is severely degraded by scattering effects, which induce signal crosstalk and a low signal-to-noise ratio in the detection process, particularly when imaging deep layers. Accordingly, the present study proposes a cross-modality learning-based neural network method for performing image registration and restoration. In the proposed method, the point-scanning multiphoton excitation microscopy images are registered to the TFMPEM images by an unsupervised U-Net model based on a global linear affine transformation process and local VoxelMorph registration network. A multi-stage 3D U-Net model with a cross-stage feature fusion mechanism and self-supervised attention module is then used to infer in-vitro fixed TFMPEM volumetric images. The experimental results obtained for in-vitro drosophila mushroom body (MB) images show that the proposed method improves the structure similarity index measures (SSIMs) of the TFMPEM images acquired with a 10-ms exposure time from 0.38 to 0.93 and 0.80 for shallow- and deep-layer images, respectively. A 3D U-Net model, pretrained on in-vitro images, is further trained using a small in-vivo MB image dataset. The transfer learning network improves the SSIMs of in-vivo drosophila MB images captured with a 1-ms exposure time to 0.97 and 0.94 for shallow and deep layers, respectively.

Adaptive enhancement of acoustic resolution photoacoustic microscopy imaging via deep CNN prior

Acoustic resolution photoacoustic microscopy (AR-PAM) is a promising medical imaging modality that can be employed for deep bio-tissue imaging. However, its relatively low imaging resolution has greatly hindered its wide applications. Previous model-based or learning-based PAM enhancement algorithms either require design of complex handcrafted prior to achieve good performance or lack the interpretability and flexibility that can adapt to different degradation models. However, the degradation model of AR-PAM imaging is subject to both imaging depth and center frequency of ultrasound transducer, which varies in different imaging conditions and cannot be handled by a single neural network model. To address this limitation, an algorithm integrating both learning-based and model-based method is proposed here so that a single framework can deal with various distortion functions adaptively. The vasculature image statistics is implicitly learned by a deep convolutional neural network, which served as plug and play (PnP) prior. The trained network can be directly plugged into the model-based optimization framework for iterative AR-PAM image enhancement, which fitted for different degradation mechanisms. Based on physical model, the point spread function (PSF) kernels for various AR-PAM imaging situations are derived and used for the enhancement of simulation and in vivo AR-PAM images, which collectively proved the effectiveness of proposed method. Quantitatively, the PSNR and SSIM values have all achieve best performance with the proposed algorithm in all three simulation scenarios; The SNR and CNR values have also significantly raised from 6.34 and 5.79 to 35.37 and 29.66 respectively in an in vivo testing result with the proposed algorithm.

A low-toxic luminescent terbium(III)-loxoprofen complex for bio-optical imaging

A novel green-emitting terbium(III)-loxoprofen complex (Tb-LPF) was synthesized via a simple solution precipitation method, and the corresponding chemical composition and structure were determined by elemental analysis and infrared absorption spectra. The thermal stability of Tb-LPF was investigated through thermogravimetric analysis. The photophysical properties of Tb-LPF were measured by UV absorption and photoluminescence spectra. Furthermore, the biological toxicity of Tb-LPF was determined using MTT assay and flow cytometry based on MCF-7 cells. The experimental results demonstrated that Tb-LPF exhibited strong green emission and low toxicity, endowing Tb-LPF with a potential capability to act as an imaging probe in optical detection and bio-tissue imaging.

Dual-Wavelength Fluorescence Monitoring of Photodynamic Therapy: From Analytical Models to Clinical Studies.

Simple SummaryFluorescence imaging is an efficient tool in monitoring photodynamic therapy procedures allowing us to track accumulation and photobleaching of a photosensitizer (PS). Chlorin-based PSs feature high absorption in the red and blue bands of visible spectrum. Due to spectral dispersion of light penetration depth in biotissues, fluorescence signals registered upon excitation by red or blue light are formed in different measurement volumes. We present analytical and numerical models of dual-wavelength fluorescence imaging for evaluation of PS localization depth in the cases of topical administration and intravenous injection. The results of analytical and numerical simulations are in good agreement with the phantom experiments, and are translated to the in vivo imaging, which allows to interpret experimental observations in animal trials, human volunteers, and clinical studies. The proposed approach allows us to noninvasively estimate typical accumulation depths of PS localization which are consistent with the morphologically expected values.Fluorescence imaging modalities are currently a routine tool for the assessment of marker distribution within biological tissues, including monitoring of fluorescent photosensitizers (PSs) in photodynamic therapy (PDT). Conventional fluorescence imaging techniques provide en-face two-dimensional images, while depth-resolved techniques require complicated tomographic modalities. In this paper, we report on a cost-effective approach for the estimation of fluorophore localization depth based on dual-wavelength probing. Owing to significant difference in optical properties of superficial biotissues for red and blue ranges of optical spectra, simultaneous detection of fluorescence excited at different wavelengths provides complementary information from different measurement volumes. Here, we report analytical and numerical models of the dual-wavelength fluorescence imaging of PS-containing biotissues considering topical and intravenous PS administration, and demonstrate the feasibility of this approach for evaluation of the PS localization depth based on the fluorescence signal ratio. The results of analytical and numerical simulations, as well as phantom experiments, were translated to the in vivo imaging to interpret experimental observations in animal experiments, human volunteers, and clinical studies. The proposed approach allowed us to estimate typical accumulation depths of PS localization which are consistent with the morphologically expected values for both topical PS administration and intravenous injection.

Low-pass filtering based polarimetric dehazing method for dense haze removal.

Polarimetric dehazing method is very promising in enhancing the quality of images captured in the scattering media. However, it is found that the dehazing results calculated by hazy images are very sensitive to the noise, which may cause the method unstable or even invalid. To overcome this drawback and enhance the capability and stability of the polarimetric dehazing method, digital image processing algorithms or bias parameters need to be added into the method, however, they will make the algorithm complex and time consuming. In this paper, using low pass filter to suppress the noise of the hazy images, a novel polarimetric dehazing method is proposed to enhance the visibility of hazy images, especially for dense haze removal. Experimental results demonstrate that this method is totally automatic and very effective in dense haze processing. This method may have great potential usage in many applications, such as optical surveillance, underwater imaging, and bio-tissue imaging, etc.

Temporal focusing multiphoton microscopy with optimized parallel multiline scanning for fast biotissue imaging.

.Significance: Line scanning-based temporal focusing multiphoton microscopy (TFMPM) has superior axial excitation confinement (AEC) compared to conventional widefield TFMPM, but the frame rate is limited due to the limitation of the single line-to-line scanning mechanism. The development of the multiline scanning-based TFMPM requires only eight multiline patterns for full-field uniform multiphoton excitation and it still maintains superior AEC.Aim: The optimized parallel multiline scanning TFMPM is developed, and the performance is verified with theoretical simulation. The system provides a sharp AEC equivalent to the line scanning-based TFMPM, but fewer scans are required.Approach: A digital micromirror device is integrated in the TFMPM system and generates the multiline pattern for excitation. Based on the result of single-line pattern with sharp AEC, we can further model the multiline pattern to find the best structure that has the highest duty cycle together with the best AEC performance.Results: The AEC is experimentally improved to from the of conventional TFMPM. The adopted multiline pattern is akin to a pulse-width-modulation pattern with a spatial period of four times the diffraction-limited line width. In other words, ideally only four spatial phase-shift scans are required to form a full two-dimensional image with superior AEC instead of image-size-dependent line-to-line scanning.Conclusions: We have demonstrated the developed parallel multiline scanning-based TFMPM has the multiline pattern for sharp AEC and the least scans required for full-field uniform excitation. In the experimental results, the temporal focusing-based multiphoton images of disordered biotissue of mouse skin with improved axial resolution due to the near-theoretical limit AEC are shown to clearly reduce background scattering.

Synthesizing Ag+: MgS, Ag+: Nb2S5, Sm3+: Y2S3, Sm3+:Er2S3, and Sm3+:ZrS2 Compound Nanoparticles for Multicolor Fluorescence Imaging of Biotissues.

Development of the fluorophores whose fluorescence bands can be flexibly selected is of great interest for biotissue imaging. Compounds of Ag+:MgS, Ag+:Nb2S5, Sm3+:Y2S3, Sm3+:Er2S3, and Sm3+:ZrS2 were obtained through new chemical synthesis. They were characterized by X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, and transmission electron microscopy. They revealed polychromatic-photoluminescence spectra when excited by 280, 380, 480, 580, 680, and 785 nm light. Especially, near-infrared emission ranging from 800–1100 nm was found upon 785 nm light excitation. A band model was proposed to explain transitions responsible for the observed components of emission. Their broad fluorescence spectra cover from the ultraviolet to near-infrared spectral range. Their ability of emitting wide-range fluorescence was utilized for multicolor fluorescence imaging of biotissues, as demonstrated by pig-kidney tissue samples.

Near Field Microwave Holography for Bio-Tissue Imaging

This study investigated the ability of microwave holography to accurately reconstruct the tissue structure of the human body. Numerical breast and head phantoms were imaged by 3D near-field holography using backscattered waves obtained by a monostatic planar scan. Complex organizational structures have been reconstructed accurately and quickly. In addition, breasts with relatively simple histology could be reconstructed without the matching liquid.

808 nm laser triggered self-monitored photo-thermal therapeutic nano-system Y2O3: Nd3+/Yb3+/Er3+@SiO2@Cu2S

A multifunctional photo-thermal therapeutic nano-platform Y 2 O 3 : Nd 3 + / Yb 3 + / Er 3 + @ SiO 2 @ Cu 2 S (YR-Si- Cu 2 S ) was designed through a core–shell structure, expressing the function of bio-tissue imaging, real-time temperature detection, and photo-thermal therapy under 808 nm light excitation. In this system, the core Y 2 O 3 : Nd 3 + / Yb 3 + / Er 3 + (YR) takes the responsibility of emitting optical information and monitoring temperature, while the shell Cu 2 S nano-particles carry most of the photo-thermal conversion function. The temperature sensing characteristic was achieved by the fluorescence intensity ratio using the thermally coupled energy levels (TCLs) S 3 / 2 4 / H 2 11 / 2 of Er 3 + , and its higher accuracy for real-time temperature measurement in the bio-tissue than that of an infrared thermal camera was also proved by sub-tissue experiments. Furthermore, the photo-thermal effect of the present nano-system Y 2 O 3 : Nd 3 + / Yb 3 + / Er 3 + @ SiO 2 @ Cu 2 S was confirmed by Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) ablation. Results indicate that YR-Si- Cu 2 S has application prospect in temperature-controlled photo-thermal treatment and imaging in bio-tissues.

Synthesis of Ag-Ho, Ag-Sm, Ag-Zn, Ag-Cu, Ag-Cs, Ag-Zr, Ag-Er, Ag-Y and Ag-Co metal organic nanoparticles for UV-Vis-NIR wide-range bio-tissue imaging.

Development of materials for fluorescence imaging with a wide optical range is important for clinical applications. In this work, a solution synthesis method was used for making Ag-Ho, Ag-Sm, Ag-Zn, Ag-Cu Ag-Cs, Ag-Zr, Ag-Er, Ag-Y and Ag-Co metal organic compound nanoparticles. XRD, XPS and TEM were carried out for sample characterization. They showed broad fluorescence from the UV to NIR region. In particular, they presented near-infrared (NIR) fluorescence (800-1100 nm) when excitation light of 785 nm was used. Furthermore, a white-to-green or blue-to-white transition was observed when excitation light varied from 290 nm to 370 nm. Proof-of-concept experiments were performed via UV light (359-371 nm), blue light (450-490 nm), green light (540-552 nm) and NIR light (center wavelength = 785 nm) excitation with pig-kidney tissue samples. They showed potential for biomedical fluorescence imaging in the UV-Vis-NIR range.

Conjugate Transformation for Dispersion Compensation in Optical Coherence Tomography Imaging

In optical coherence tomography (OCT), the sample dispersion tends to increase the signal width and hence lower down the resolution, resulting in serious image quality degradation, especially for imaging over a large depth range or media with large dispersion coefficient. In this letter, instead of the conventional Fourier transformation for dispersion compensation that can compensate the image only ideally at a certain depth, a novel transformation, as called conjugate transformation, is proposed to achieve high resolution at all depth by utilizing the conjugate function of the signal itself as an optimized integral kernel. A large dispersion media of ZnSe is used as the sample to test the feasibility of this novel transformation, achieving ∼1.4 times higher resolution than the conventional transformation. OCT imaging of bio-tissues with ideally compensation of sample dispersion for all the depth is experimentally demonstrated and at the same time the dispersion coefficients are also obtained.

A high-performance bio-tissue imaging method using air flow-assisted desorption electrospray ionization coupled with a high-resolution mass spectrometer

Mass spectrometry imaging (MSI) technology can simultaneously obtain the spatial distribution of thousands of chemical compounds and has unique advantages compared to other techniques that allow mapping the surface of bio-tissue. Here, we combined an air flow-assisted desorption electrospray ionization (AFADESI) MSI device with a high-resolution mass spectrometer to optimize the system parameters and achieve more accurate spatial distribution characteristics for compounds of interest while investigating bio-tissue sections. The platform set-up, required instrumentation, sample pretreatment, parameter optimization and bio-tissue characterization are described and discussed. Finally, the parameter conditions that can provide optimal ionic intensity and enhanced resolution were confirmed. The reasonable resolution and sensitivity improvements of AFADESI-MSI have been achieved through tandem a high-resolution mass spectrometer system, therefore, it would be a promising technique for the bio-tissue imaging analysis.

Broadband High-Energy All-Fiber Laser at 1.6 $\mu$ m

A broadband high-energy all-fiber laser at 1.6- $\mu \text{m}$ window with erbium-doped fiber mode locked by nonlinear polarization rotation technology is demonstrated. The direct output optical spectrum centered at 1.6 $\mu \text{m}$ has a bandwidth of 52.4 nm. The fiber laser delivers a pulse energy of 3.9 nJ with 9.3-MHz repetition rate at 220-mW 976-nm pump power. Based on it, a wavelength-tunable optical source with a wavelength tuning range from 1.6 to 1.8 $\mu \text{m}$ is demonstrated through soliton self-frequency shift. To satisfy much longer wavelength demands in some special application scenario, e.g., deep brain imaging with multi-photon microscopy, a chirped pulse amplifier was constructed to boost the pulse energy to 14 nJ, and the wavelength can be tuned from 1.6 to 1.94 $\mu \text{m}$ with those amplified pulses. These fiber sources at the $L$ -band and a longer wavelength can explore a wider scope in deep biotissue imaging area for lower water absorption.

Fundamentals of optical coherence tomography: a critical review

The main objective of this work is to go through fundamentals, mechanism and types of the state of the art emerging imaging modality i.e. optical coherence tomography (OCT) for non-invasive 3D imaging of bio tissues. This work consists of literature studied critically for OCT’s contribution in axial scanning of bio tissues with it different types to the best of our knowledge. Doppler optical coherence tomography (D-OCT) and speckle variance optical coherence tomography (SV-OCT) for blood flow assessment and blood microvasculatures on micron-scale resolution with dorsal skin-fold window chamber model (WCM) of mouse, Fourier domain common path (FD-CP-OCT) for applications in the setting of delicate microsurgical procedures such as intraocular retinal surgery have been explored. We conclude that OCT is the promised imaging modality in 3D regime for non-invasive applications.

Optical coherence tomography in gynecology: a narrative review.

Modern gynecologic practice requires noninvasive diagnostics techniques capable of detecting morphological and functional alterations in tissues of female reproductive organs. Optical coherence tomography (OCT) is a promising tool for providing imaging of biotissues with high resolution at depths up to 2mm. Design of the customized probes provides wide opportunities for OCT use in gynecology. This paper contains a retrospective insight into the history of OCT employment in gynecology, an overview of the existing gynecologic OCT probes, including those for combination with other diagnostic modalities, and state-of-the-art application of OCT for diagnostics of tumor and nontumor pathologies of female genitalia. Perspectives of OCT both in diagnostics and treatment planning and monitoring in gynecology are overviewed.

Temporal focusing-based widefield multiphoton microscopy with spatially modulated illumination for biotissue imaging.

A developed temporal focusing-based multiphoton excitation microscope (TFMPEM) has a digital micromirror device (DMD) which is adopted not only as a blazed grating for light spatial dispersion but also for patterned illumination simultaneously. Herein, the TFMPEM has been extended to implement spatially modulated illumination at structured frequency and orientation to increase the beam coverage at the back-focal aperture of the objective lens. The axial excitation confinement (AEC) of TFMPEM can be condensed from 3.0 μm to 1.5 μm for a 50 % improvement. By using the TFMPEM with HiLo technique as two structured illuminations at the same spatial frequency but different orientation, reconstructed biotissue images according to the condensed AEC structured illumination are shown obviously superior in contrast and better scattering suppression. Picture: TPEF images of the eosin-stained mouse cerebellar cortex by conventional TFMPEM (left), and the TFMPEM with HiLo technique as 1.09 μm-1 spatially modulated illumination at 90° (center) and 0° (right) orientations.

Inverse focusing inside turbid media by creating an opposite virtual objective.

Limited by the penetration depth, imaging of thick bio-tissues can be achieved only by epi-detection geometry. Applications based on forward-emitted signals or bidirectional illumination are restricted by lack of an opposite objective. A method for creating an opposite virtual objective inside thick media through phase conjugation was first proposed. Under forward illumination, the backward scattering light from the media was collected to generate a phase conjugate wave, which was sent back to the media and formed an inverse focusing light. Samples combined with a diffuser or a mouse skin were used as specimens. Inverse focusing was successfully demonstrated by applying holography-based optical phase conjugation with a BaTiO3. This result indicates the capability to create an opposite virtual objective inside live tissues. The proposed method is compatible with current coherent imaging and super-resolution imaging technologies. It creates a possible way for forward-emitted signals collection and bidirectional illumination in thick specimens.

Enhanced spatial resolution in optical imaging of biotissues labelled with upconversion nanoparticles using a fibre-optic probe scanning technique

The new generation of synthetic nanomaterials, upconversion nanoparticles (UCNPs), have the potential for high-contrast optical imaging of biological tissue by virtue of their unique luminescent properties which enable the autofluorescence and excitation signals to be completely suppressed and avoid biotissue absorption. The potential for deep tissue imaging, such as whole animal imaging, is demonstrated in this report on a comparative study of two epiluminescent imaging methods suitable for the localization of a UCNP-labelled pathology site buried in highly scattering biological tissue modelled by an optical tissue phantom. The lateral resolution exhibited in scanning imaging by an illumination-collection fibre-optic probe appeared to be almost 1.73 times better than that shown by the wide-field CCD commonly used in diffuse optical tomography systems. We attribute this improved lateral resolution to the enhanced angular selectivity of the illumination-collection regime and to the nonlinear dependence of the UCNP luminescence on the excitation intensity.

Synthesis and biotissue imaging of water-soluble boron-dipyrromethene fluorophore

目的 长波吸收和发射的水溶性荧光染料被广泛应用于生物技术和生物医学领域,如DNA排序、诊断成像和光动力治疗等.方法 为了开发具有近红外荧光特性的分子探针,通过Knoevenagel缩合反应合成一种新型水溶性荧光化合物——荧光染料(BODIPY)；评价了其光学性能,并以裸鼠为实验动物评价了该探针在生物组织成像中的效果.结果 这类荧光化合物具有良好的水溶性和光学性能,对正常裸鼠深层组织和脏器具有明显成像效果.结论 该类探针在荧光影像学诊断方面具有很好的应用潜力。