Computational conjugate adaptive optics microscopy for longitudinal through-skull imaging of cortical myelin

Myelination processes are closely related to higher brain functions such as learning and memory. While their longitudinal observation has been crucial to understanding myelin-related physiology and various brain disorders, skull opening or thinning has been required to secure clear optical access. Here we present a high-speed reflection matrix microscope using a light source with a wavelength of 1.3 μm to reduce tissue scattering and aberration. Furthermore, we develop a computational conjugate adaptive optics algorithm designed for the recorded reflection matrix to optimally compensate for the skull aberrations. These developments allow us to realize label-free longitudinal imaging of cortical myelin through an intact mouse skull. The myelination processes of the same mice were observed from 3 to 10 postnatal weeks to the depth of cortical layer 4 with a spatial resolution of 0.79 μm. Our system will expedite the investigations on the role of myelination in learning, memory, and brain disorders.

HyU: Hybrid Unmixing for longitudinal in vivo imaging of low signal-to-noise fluorescence

The expansion of fluorescence bioimaging toward more complex systems and geometries requires analytical tools capable of spanning widely varying timescales and length scales, cleanly separating multiple fluorescent labels and distinguishing these labels from background autofluorescence. Here we meet these challenging objectives for multispectral fluorescence microscopy, combining hyperspectral phasors and linear unmixing to create Hybrid Unmixing (HyU). HyU is efficient and robust, capable of quantitative signal separation even at low illumination levels. In dynamic imaging of developing zebrafish embryos and in mouse tissue, HyU was able to cleanly and efficiently unmix multiple fluorescent labels, even in demanding volumetric timelapse imaging settings. HyU permits high dynamic range imaging, allowing simultaneous imaging of bright exogenous labels and dim endogenous labels. This enables coincident studies of tagged components, cellular behaviors and cellular metabolism within the same specimen, providing more accurate insights into the orchestrated complexity of biological systems.

Open-source statistical and data processing tools for wide-field optical imaging data in mice

Significance

Wide-field optical imaging (WOI) can produce concurrent hemodynamic and cell-specific calcium recordings across the entire cerebral cortex in animal models. There have been multiple studies using WOI to image mouse models with various environmental or genetic manipulations to understand various diseases. Despite the utility of pursuing mouse WOI alongside human functional magnetic resonance imaging (fMRI), and the multitude of analysis toolboxes in the fMRI literature, there is not an available open-source, user-friendly data processing and statistical analysis toolbox for WOI data.

Aim

To assemble a MATLAB toolbox for processing WOI data, as described and adapted to combine techniques from multiple WOI groups and fMRI.

Approach

We outline our MATLAB toolbox on GitHub with multiple data analysis packages and translate a commonly used statistical approach from the fMRI literature to the WOI data. To illustrate the utility of our MATLAB toolbox, we demonstrate the ability of the processing and analysis framework to detect a well-established deficit in a mouse model of stroke and plot activation areas during an electrical paw stimulus experiment.

Results

Our processing toolbox and statistical methods isolate a somatosensory-based deficit 3 days following photothrombotic stroke and cleanly localize sensory stimulus activations.

Conclusions

The toolbox presented here details an open-source, user-friendly compilation of WOI processing tools with statistical methods to apply to any biological question investigated with WOI techniques.

Comparison of surface dose during whole breast radiation therapy on Halcyon and TrueBeam using Cherenkov imaging

The emergence of the Halcyon linear accelerator has allowed for increased patient throughput and improved treatment times for common treatment sites in radiation oncology. However, it has been shown that this can lead to increased surface dose in sites like breast cancer compared with treatments on conventional machines with flattened radiation beams. Cherenkov imaging can be used to estimate surface dose by detection of Cherenkov photons emitted in proportion to energy deposition from high energy electrons in tissue. Phantom studies were performed with both square beams in reference conditions and with clinical treatments, and dosimeter readings and Cherenkov images report higher surface dose (25% for flat phantom entrance dose, 5.9% for breast phantom treatment) from Halcyon beam deliveries than for equivalent deliveries from a TrueBeam linac. Additionally, the first Cherenkov images of a patient treated with Halcyon were acquired, and superficial dose was estimated.

Engineered Nanoprobes for Immune Activation Monitoring

The activation of the immune system is critical for cancer immunotherapy and treatments of inflammatory diseases. Non-invasive visualization of immunoactivation is designed to monitor the dynamic nature of the immune response and facilitate the assessment of therapeutic outcomes, which, however, remains challenging. Conventional imaging modalities, such as positron emission tomography, computed tomography, etc., were utilized for imaging immune-related biomarkers. To explore the dynamic immune monitoring, probes with signals correlated to biomarkers of immune activation or prognosis are urgently needed. These emerging molecular probes, which turn on the signal only in the presence of the intended biomarker, can improve the detection specificity. These probes with "turn on" signals enable non-invasive, dynamic, and real-time imaging with high sensitivity and efficiency, showing significance for multifunctionality/multimodality imaging. As a result, more and more innovative engineered nanoprobes combined with diverse imaging modalities were developed to assess the activation of the immune system. In this work, we comprehensively review the recent and emerging advances in engineered nanoprobes for monitoring immune activation in cancer or other immune-mediated inflammatory diseases and discuss the potential in predicting the efficacy following treatments. Research on real-time in vivo immunoimaging is still under exploration, and this review can provide guidance and facilitate the development and application of next-generation imaging technologies.

Rapid and label-free histological imaging of unprocessed surgical tissues via dark-field reflectance ultraviolet microscopy

Routine examination for intraoperative histopathologic assessment is lengthy and laborious. Here, we present the dark-field reflectance ultraviolet microscopy (DRUM) that enables label-free imaging of unprocessed and thick tissues with subcellular resolution and a high signal-to-background ratio. To the best of our knowledge, DRUM provides image results for pathological assessment with the shortest turnaround time (2-3 min in total from sample preparation to tissue imaging). We also proposed a virtual staining process to convert DRUM images into pseudo-colorized images and enhance the image familiarity of pathologists. By imaging various tissues, we found DRUM can resolve cell nuclei and some extranuclear features, which are comparable to standard H&E images. Furthermore, the essential diagnostic features of intraoperatively excised tumor tissues also can be revealed by DRUM, demonstrating its potential as an additional aid for intraoperative histopathology.

Optical transparency and label-free vessel imaging of zebrafish larvae in shortwave infrared range as a tool for prolonged studying of cardiovascular system development

Optical techniques are utilized for the non-invasive analysis of the zebrafish cardiovascular system at early developmental stages. Being based mainly on conventional optical microscopy components and image sensors, the wavelength range of the collected and analyzed light is not out of the scope of 400-900 nm. In this paper, we compared the non-invasive optical approaches utilizing visible and near infrared range (VISNIR) 400-1000 and the shortwave infrared range (SWIR) 900-1700 nm. The transmittance spectra of zebrafish tissues were measured in these wavelength ranges, then vessel maps, heart rates, and blood flow velocities were calculated from data in VISNIR and SWIR. An increased pigment pattern transparency was registered in SWIR, while the heart and vessel detection quality in this range is not inferior to VISNIR. Obtained results indicate an increased efficiency of SWIR imaging for monitoring heart function and hemodynamic analysis of zebrafish embryos and larvae and suggest a prolonged registration period in this range compared to other optical techniques that are limited by pigment pattern development.

Osteosarcoma-Derived Exosomes as Potential PET Imaging Nanocarriers for Lung Metastasis

Lung metastases represent the most adverse clinical factor and rank as the leading cause of osteosarcoma-related death. Nearly 80% of patients present lung micrometastasis at diagnosis not detected with current clinical tools. Herein, an exosome (EX)-based imaging tool is developed for lung micrometastasis by positron emission tomography (PET) using osteosarcoma-derived EXs as natural nanocarriers of the positron-emitter copper-64 (⁶⁴ Cu). Exosomes are isolated from metastatic osteosarcoma cells and functionalized with the macrocyclic chelator NODAGA for complexation with ⁶⁴ Cu. Surface functionalization has no effect on the physicochemical properties of EXs, or affinity for donor cells and endows them with favorable pharmacokinetics for in vivo studies. Whole-body PET/magnetic resonance imaging (MRI) images in xenografted models show a specific accumulation of ⁶⁴ Cu-NODAGA-EXs in metastatic lesions as small as 2-3 mm or in a primary tumor, demonstrating the exquisite tropism of EXs for homotypic donor cells. The targetability for lung metastasis is also observed by optical imaging using indocyanine green (ICG)-labeled EXs and D-luciferin-loaded EXs. These findings show that tumor-derived EXs hold great potential as targeted imaging agents for the noninvasive detection of small lung metastasis by PET. This represents a step forward in the biomedical application of EXs in imaging diagnosis with increased translational potential.

Single-Particle Optical Imaging for Ultrasensitive Bioanalysis

The quantitative detection of critical biomolecules and in particular low-abundance biomarkers in biofluids is crucial for early-stage diagnosis and management but remains a challenge largely owing to the insufficient sensitivity of existing ensemble-sensing methods. The single-particle imaging technique has emerged as an important tool to analyze ultralow-abundance biomolecules by engineering and exploiting the distinct physical and chemical property of individual luminescent particles. In this review, we focus and survey the latest advances in single-particle optical imaging (OSPI) for ultrasensitive bioanalysis pertaining to basic biological studies and clinical applications. We first introduce state-of-the-art OSPI techniques, including fluorescence, surface-enhanced Raman scattering, electrochemiluminescence, and dark-field scattering, with emphasis on the contributions of various metal and nonmetal nano-labels to the improvement of the signal-to-noise ratio. During the discussion of individual techniques, we also highlight their applications in spatial-temporal measurement of key biomarkers such as proteins, nucleic acids and extracellular vesicles with single-entity sensitivity. To that end, we discuss the current challenges and prospective trends of single-particle optical-imaging-based bioanalysis.

Studying the trafficking of labeled trodusquemine and its application as nerve marker for light-sheet and expansion microscopy

Trodusquemine is an aminosterol with a variety of biological and pharmacological functions, such as acting as an antimicrobial, stimulating body weight loss and interfering with the toxicity of proteins involved in the development of Alzheimer's and Parkinson's diseases. The mechanisms of interaction of aminosterols with cells are, however, still largely uncharacterized. Here, by using fluorescently labeled trodusquemine (TRO-A594 and TRO-ATTO565), we show that trodusquemine binds initially to the plasma membrane of living cells, that the binding affinity is dependent on cholesterol, and that trodusquemine is then internalized and mainly targeted to lysosomes after internalization. We also found that TRO-A594 is able to strongly and selectively bind to myelinated fibers in fixed mouse brain slices, and that it is a marker compatible with tissue clearing and light-sheet fluorescence microscopy or expansion microscopy. In conclusion, this work contributes to further characterize the biology of aminosterols and provides a new tool for nerve labeling suitable for the most advanced microscopy techniques.

Disturbed microcirculation and hyperaemic response in a murine model of systemic inflammation

Systemic inflammation affects cognitive functions and increases the risk of dementia. This phenomenon is thought to be mediated in part by cytokines that promote neuronal survival, but the continuous exposure to which may lead to neurodegeneration. The effects of systemic inflammation on cerebral blood vessels, and their provision of adequate oxygen to support critical brain parenchymal cell functions, remains unclear. Here, we demonstrate that neurovascular coupling is profoundly disturbed in lipopolysaccharide (LPS) induced systemic inflammation in awake mice. In the 24 hours following LPS injection, the hyperaemic response of pial vessels to functional activation was attenuated and delayed. Concurrently, under steady-state conditions, the capillary network displayed a significant increase in the number of capillaries with blocked blood flow, as well as increased duration of 'capillary stalls'-a phenomenon previously reported in animal models of stroke and Alzheimer's disease pathology. We speculate that vascular changes and impaired oxygen availability may affect brain functions following acute systemic inflammation and contribute to the long-term risk of neurodegenerative changes associated with chronic, systemic inflammation.

Image-seq: spatially resolved single-cell sequencing guided by in situ and in vivo imaging

Tissue function depends on cellular organization. While the properties of individual cells are increasingly being deciphered using powerful single-cell sequencing technologies, understanding their spatial organization and temporal evolution remains a major challenge. Here, we present Image-seq, a technology that provides single-cell transcriptional data on cells that are isolated from specific spatial locations under image guidance, thus preserving the spatial information of the target cells. It is compatible with in situ and in vivo imaging and can document the temporal and dynamic history of the cells being analyzed. Cell samples are isolated from intact tissue and processed with state-of-the-art library preparation protocols. The technique therefore combines spatial information with highly sensitive RNA sequencing readouts from individual, intact cells. We have used both high-throughput, droplet-based sequencing as well as SMARTseq-v4 library preparation to demonstrate its application to bone marrow and leukemia biology. We discovered that DPP4 is a highly upregulated gene during early progression of acute myeloid leukemia and that it marks a more proliferative subpopulation that is confined to specific bone marrow microenvironments. Furthermore, the ability of Image-seq to isolate viable, intact cells should make it compatible with a range of downstream single-cell analysis tools including multi-omics protocols.

Clickable C-Glycosyl Scaffold for the Development of a Dual Fluorescent and [(18)F]fluorinated Cyanine-Containing Probe and Preliminary In Vitro/Vivo Evaluation by Fluorescence Imaging

Considering the individual characteristics of positron emission tomography (PET) and optical imaging (OI) in terms of sensitivity, spatial resolution, and tissue penetration, the development of dual imaging agents for bimodal PET/OI imaging is a growing field. A current major breakthrough in this field is the design of monomolecular agent displaying both a radioisotope for PET and a fluorescent dye for OI. We took advantage of the multifunctionalities allowed by a clickable C-glycosyl scaffold to gather the different elements. We describe, for the first time, the synthesis of a cyanine-based dual PET/OI imaging probe based on a versatile synthetic strategy and its direct radiofluorination via [¹⁸F]F-C bond formation. The non-radioactive dual imaging probe coupled with two c(RGDfK) peptides was evaluated in vitro and in vivo in fluorescence imaging. The binding on α_vβ₃ integrin (IC₅₀ = 16 nM) demonstrated the efficiency of the dimeric structure and PEG linkers in maintaining the affinity. In vivo fluorescence imaging of U-87 MG engrafted nude mice showed a high tumor uptake (40- and 100-fold increase for orthotopic and ectopic brain tumors, respectively, compared to healthy brain). In vitro and in vivo evaluations and resection of the ectopic tumor demonstrated the potential of the conjugate in glioblastoma cancer diagnosis and image-guided surgery.

Multi-modal retinal scanning to measure retinal thickness and peripheral blood vessels in multiple sclerosis

Our purpose was to investigate changes to the retina in multiple sclerosis (MS) using established and novel modes of retinal image acquisition and analysis. 72 participants with MS and 80 healthy volunteers underwent retinal scanning with optical coherence tomography (OCT) and ultra-widefield (UWF) scanning laser ophthalmoscopy (SLO), over a two-year period. Changes in retinal nerve fibre layer (RNFL) thickness, macular volume and retinal blood vessel diameter were measured and parameters were then tested for associations with MS. Measurements from OCT showed that individuals with MS had a thinner RNFL and reduced macular volume when compared to healthy volunteers. On UWF images, participants with MS had reduced arterial widths in the inferior nasal quadrant of both eyes and reduced venous widths in the inferior nasal quadrant of right eyes. Longitudinal analysis showed that participants with MS had an accelerated annual rate of RNFL thinning in several regions of the retina. In conclusion, the assessment of OCT showed thinning of the RNFL and macula in concordance with previous reports on MS, while analysis of blood vessels in the retinal periphery from UWF-SLO images revealed novel changes.

Label-free multimodal imaging of infected Galleria mellonella larvae

Non-linear imaging modalities have enabled us to obtain unique morpho-chemical insights into the tissue architecture of various biological model organisms in a label-free manner. However, these imaging techniques have so far not been applied to analyze the Galleria mellonella infection model. This study utilizes for the first time the strength of multimodal imaging techniques to explore infection-related changes in the Galleria mellonella larvae due to massive E. faecalis bacterial infection. Multimodal imaging techniques such as fluorescent lifetime imaging (FLIM), coherent anti-Stokes Raman scattering (CARS), two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) were implemented in conjunction with histological HE images to analyze infection-associated tissue damage. The changes in the larvae in response to the infection, such as melanization, vacuolization, nodule formation, and hemocyte infiltration as a defense mechanism of insects against microbial pathogens, were visualized after Enterococcus faecalis was administered. Furthermore, multimodal imaging served for the analysis of implant-associated biofilm infections by visualizing biofilm adherence on medical stainless steel and ePTFE implants within the larvae. Our results suggest that infection-related changes as well as the integrity of the tissue of G. mellonella larvae can be studied with high morphological and chemical contrast in a label-free manner.

Wing Interferential Patterns (WIPs) and machine learning, a step toward automatized tsetse (Glossina spp.) identification

A simple method for accurately identifying Glossina spp in the field is a challenge to sustain the future elimination of Human African Trypanosomiasis (HAT) as a public health scourge, as well as for the sustainable management of African Animal Trypanosomiasis (AAT). Current methods for Glossina species identification heavily rely on a few well-trained experts. Methodologies that rely on molecular methodologies like DNA barcoding or mass spectrometry protein profiling (MALDI TOFF) haven't been thoroughly investigated for Glossina sp. Nevertheless, because they are destructive, costly, time-consuming, and expensive in infrastructure and materials, they might not be well adapted for the survey of arthropod vectors involved in the transmission of pathogens responsible for Neglected Tropical Diseases, like HAT. This study demonstrates a new type of methodology to classify Glossina species. In conjunction with a deep learning architecture, a database of Wing Interference Patterns (WIPs) representative of the Glossina species involved in the transmission of HAT and AAT was used. This database has 1766 pictures representing 23 Glossina species. This cost-effective methodology, which requires mounting wings on slides and using a commercially available microscope, demonstrates that WIPs are an excellent medium to automatically recognize Glossina species with very high accuracy.

White blood cell detection, classification and analysis using phase imaging with computational specificity (PICS)

Treatment of blood smears with Wright's stain is one of the most helpful tools in detecting white blood cell abnormalities. However, to diagnose leukocyte disorders, a clinical pathologist must perform a tedious, manual process of locating and identifying individual cells. Furthermore, the staining procedure requires considerable preparation time and clinical infrastructure, which is incompatible with point-of-care diagnosis. Thus, rapid and automated evaluations of unlabeled blood smears are highly desirable. In this study, we used color spatial light interference microcopy (cSLIM), a highly sensitive quantitative phase imaging (QPI) technique, coupled with deep learning tools, to localize, classify and segment white blood cells (WBCs) in blood smears. The concept of combining QPI label-free data with AI for the purpose of extracting cellular specificity has recently been introduced in the context of fluorescence imaging as phase imaging with computational specificity (PICS). We employed AI models to first translate SLIM images into brightfield micrographs, then ran parallel tasks of locating and labelling cells using EfficientNet, which is an object detection model. Next, WBC binary masks were created using U-net, a convolutional neural network that performs precise segmentation. After training on digitally stained brightfield images of blood smears with WBCs, we achieved a mean average precision of 75% for localizing and classifying neutrophils, eosinophils, lymphocytes, and monocytes, and an average pixel-wise majority-voting F1 score of 80% for determining the cell class from semantic segmentation maps. Therefore, PICS renders and analyzes synthetically stained blood smears rapidly, at a reduced cost of sample preparation, providing quantitative clinical information.

MAX: a simple, affordable, and rapid tissue clearing reagent for 3D imaging of wide variety of biological specimens

Transparency of biological specimens is crucial to obtaining detailed 3-dimensional images and understanding the structure and function of biological specimens. This transparency or tissue clearing can be achieved by adjusting the refractive index (RI) with embedding media and removing light barriers such as lipids, inorganic deposits, and pigments. Many currently available protocols consist of multiple steps to achieve sufficient transparency, making the process complex and time-consuming. Thus, in this study, we tailored the recipe for RI adjustment media named MAX based on the recently reported MACS protocol to achieve a single-step procedure, especially for ECM-rich tissues. This was achieved by the improvement of the tissue penetrability of the RI-matching reagent by combining MXDA with sucrose or iodixanol. While this was sufficient for the 3D imaging in many applications, MAX can also be combined with modular processes for de-lipidation, de-coloration, and de-calcification to further maximize the transparency depending on the special features of the tissues. Our approach provides an easy alternative for tissue clearing and 3D imaging.

Generation of bright autobioluminescent bacteria by chromosomal integration of the improved lux operon ilux2

The bacterial bioluminescence system enables the generation of light by living cells without the requirement of an external luciferin. Due to the relatively low light emission, many applications of bioluminescence imaging would benefit from an increase in brightness of this system. In this report, a new approach of mutagenesis and screening of the involved proteins is described that is based on the identification of mutants with improved properties under rate-limiting reaction conditions. Multiple rounds of screening in Escherichia coli resulted in the operon ilux2 that contains 26 new mutations in the fatty acid reductase complex which provides the aldehyde substrate for the bioluminescence reaction. Chromosomal integration of ilux2 yielded an autonomously bioluminescent E. coli strain with sixfold increased brightness compared to the previously described ilux operon. The ilux2 strain produces sufficient signal for the robust detection of individual cells and enables highly sensitive long-term imaging of bacterial propagation without a selection marker.

Extrasynaptic signaling enables an asymmetric juvenile motor circuit to produce symmetric undulation

In many animals, there is a direct correspondence between the motor patterns that drive locomotion and the motor neuron innervation. For example, the adult C. elegans moves with symmetric and alternating dorsal-ventral bending waves arising from symmetric motor neuron input onto the dorsal and ventral muscles. In contrast to the adult, the C. elegans motor circuit at the juvenile larval stage has asymmetric wiring between motor neurons and muscles but still generates adult-like bending waves with dorsal-ventral symmetry. We show that in the juvenile circuit, wiring between excitatory and inhibitory motor neurons coordinates the contraction of dorsal muscles with relaxation of ventral muscles, producing dorsal bends. However, ventral bending is not driven by analogous wiring. Instead, ventral muscles are excited uniformly by premotor interneurons through extrasynaptic signaling. Ventral bends occur in anti-phasic entrainment to activity of the same motor neurons that drive dorsal bends. During maturation, the juvenile motor circuit is replaced by two motor subcircuits that separately drive dorsal and ventral bending. Modeling reveals that the juvenile's immature motor circuit is an adequate solution to generate adult-like dorsal-ventral bending before the animal matures. Developmental rewiring between functionally degenerate circuit solutions, which both generate symmetric bending patterns, minimizes behavioral disruption across maturation.

Label-free third harmonic generation imaging and quantification of lipid droplets in live filamentous fungi

We report the utilization of Third-Harmonic Generation microscopy for label-free live cell imaging of lipid droplets in the hypha of filamentous fungus Phycomyces blakesleeanus. THG microscopy images showed bright spherical features dispersed throughout the hypha cytoplasm in control conditions and a transient increase in the number of bright features after complete nitrogen starvation. Colocalization analysis of THG and lipid-counterstained images disclosed that the cytoplasmic particles were lipid droplets. Particle Size Analysis and Image Correlation Spectroscopy were used to quantify the number density and size of lipid droplets. The two analysis methods both revealed an increase from 16 × 10^-3 to 23 × 10^-3 lipid droplets/µm² after nitrogen starvation and a decrease in the average size of the droplets (range: 0.5-0.8 µm diameter). In conclusion, THG imaging, followed by PSA and ICS, can be reliably used for filamentous fungi for the in vivo quantification of lipid droplets without the need for labeling and/or fixation. In addition, it has been demonstrated that ICS is suitable for THG microscopy.

Long-term monitoring of intravital biological processes using fluorescent protein-assisted NIR-II imaging

High spatial resolution, low background, and deep tissue penetration have made near-infrared II (NIR-II) fluorescence imaging one of the most critical tools for in vivo observation and measurement. However, the relatively short retention time and potential toxicity of synthetic NIR-II fluorophores limit their long-term application. Here, we report the use of infrared fluorescent proteins (iRFPs) as in vitro and in vivo NIR-II probes permitting prolonged continuous imaging (up to 15 months). As a representative example, iRFP713 is knocked into the mouse genome to generate a transgenic model to allow temporal and/or spatial expression control of the probe. To demonstrate its feasibility in a genuine diagnostic context, we adopt two liver regeneration models and successfully track the process for a week. The performance and monitoring efficacy are comparable to those of μCT and superior to those of indocyanine green dye. We are also able to effectively observe the pancreas, despite its deep location, under both physiological and pathological conditions. These results indicate that the iRFP-assisted NIR-II fluorescence system is suitable for monitoring various tissues and in vivo biological processes, providing a powerful noninvasive long-term imaging platform.

Optical gearbox enabled versatile multiscale high-throughput multiphoton functional imaging

To understand the function and mechanism of biological systems, it is crucial to observe the cellular dynamics at high spatiotemporal resolutions within live animals. The recent advances in genetically encoded function indicators have significantly improved the response rate to a near millisecond time scale. However, the widely employed in vivo imaging systems often lack the temporal solution to capture the fast biological dynamics. To broadly enable the capability of high-speed in vivo deep-tissue imaging, we developed an optical gearbox. As an add-on module, the optical gearbox can convert the common multiphoton imaging systems for versatile multiscale high-throughput imaging applications. In this work, we demonstrate in vivo 2D and 3D function imaging in mammalian brains at frame rates ranging from 50 to 1000 Hz. The optical gearbox's versatility and compatibility with the widely employed imaging components will be highly valuable to a variety of deep tissue imaging applications.

Assessing jugular venous compliance with optical hemodynamic imaging by modulating intrathoracic pressure

SIGNIFICANCE

The internal jugular veins (IJV) are critical cerebral venous drainage pathways that are affected by right heart function. Cardiovascular disease and microgravity can alter central venous pressure (CVP) and venous return, which may contribute to increased intracranial pressure and decreased cardiac output. Assessing jugular venous compliance may provide insight into cerebral drainage and right heart function, but monitoring changes in vessel volume is challenging.

AIM

We investigated the feasibility of quantifying jugular venous compliance from jugular venous attenuation (JVA), a noncontact optical measurement of blood volume, along with CVP from antecubital vein cannulation.

APPROACH

CVP was progressively increased through a guided graded Valsalva maneuver, increasing mouth pressure by 2 mmHg every 2 s until a maximum expiratory pressure of 20 mmHg. JVA was extracted from a 1-cm segment between the clavicle and midneck. The contralateral IJV cross-sectional area (CSA) was measured with ultrasound to validate changes in the vessel size. Compliance was calculated using both JVA and CSA between four-beat averages over the duration of the maneuver.

RESULTS

JVA and CSA were strongly correlated (median and interquartile range) over the Valsalva maneuver across participants (r = 0.986, [0.983, 0.987]). CVP more than doubled on average between baseline and peak strain (10.7 ± 4.4 vs. 25.8 ± 5.4 cmH2O; p < 0.01). JVA and CSA increased nonlinearly with CVP, and both JVA- and CSA-derived compliance decreased progressively from baseline to peak strain (49% and 56% median reduction, respectively), with no significant difference in compliance reduction between the two measures (Z = - 1.24, p = 0.21). Pressure-volume curves showed a logarithmic relationship in both CSA and JVA.

CONCLUSIONS

Optical jugular vein assessment may provide new ways to assess jugular distention and cardiac function.

Optical coherence tomography evaluation of vaginal epithelial thickness during CO2 laser treatment: A pilot study

Genitourinary syndrome of menopause (GSM) negatively affects more than half of postmenopausal women. Energy-based therapy has been explored as a minimally invasive treatment for GSM; however, its mechanism of action and efficacy is controversial. Here, we report on a pilot imaging study conducted on a small group of menopause patients undergoing laser treatment. Intravaginal optical coherence tomography (OCT) endoscope was used to quantitatively monitor the changes in the vaginal epithelial thickness (VET) during fractional-pixel CO2 laser treatment. Eleven patients with natural menopause and one surgically induced menopause patient were recruited in this clinical study. Following the laser treatment, 6 out of 11 natural menopause patient showed increase in both proximal and distal VET, while two natural menopause patient showed increase in VET in only one side of vaginal tract. Furthermore, the patient group that showed increased VET had thinner baseline VET compared to the patients that showed decrease in VET after laser treatment. These results demonstrate the potential utility of intravaginal OCT endoscope in evaluating the vaginal tissue integrity and tailoring vaginal laser treatment on a per-person basis, with the potential to monitor other treatment procedures.

Acute effects of coffee consumption on the microcirculation of macula and optic nerve head

Purpose: This study aimed to evaluate the acute changes in retinal vasculature following coffee consumption. Methods: This is an interventional case series. The subjects were 22 healthy young adults. They were asked to rest in a silent room for 15 min; then, their heart rate, blood pressure, and arterial oxygen saturation pressure were measured with a single patient monitoring system. Optical coherence tomography (OCT) and OCT angiography (OCT-A) imaging of the disc and macula were performed for both eyes of the subjects. These measurements were repeated 45 min after drinking a cup of 450 ml of coffee containing a standard dose of 130 mg of caffeine. Macular and optic nerve head neurovasculature changes were assessed. Results: The results of our study did not show a significant change in peripapillary retinal nerve fiber layer thickness and neural structural and vascular parameters of the optic nerve head. Although assessments of macular vasculature showed a significant decrement in superficial (p = 0.01) and deep vessel density (p = 0.05) at parafovea, vessel densities (VDs) at the fovea, and deep capillary plexus at perifovea showed no significant change. Conclusion: Consuming one cup of coffee (150 mg caffeine) statistically changes central foveal thickness and parafoveal blood flow but likely does not have a clinical impact in healthy young adults.

Recent advancement of imaging strategies of the lymphatic system: Answer to the decades old questions

The role of the lymphatic system in maintaining tissue homeostasis and a number of different pathophysiological conditions has been well established. The complex and delicate structure of the lymphatics along with the limitations of conventional imaging techniques make lymphatic imaging particularly difficult. Thus, in-depth high-resolution imaging of lymphatic system is key to understanding the progression of lymphatic diseases and cancer metastases and would greatly benefit clinical decisions. In recent years, the advancement of imaging technologies and development of new tracers suitable for clinical applications has enabled imaging of the lymphatic system in both clinical and pre-clinical settings. In this current review, we have highlighted the advantages and disadvantages of different modern techniques such as near infra-red spectroscopy (NIRS), positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI) and fluorescence optical imaging, that has significantly impacted research in this field and has led to in-depth insights into progression of pathological states. This review also highlights the use of current imaging technologies, and tracers specific for immune cell markers to identify and track the immune cells in the lymphatic system that would help understand disease progression and remission in immune therapy regimen.

Optimal combinations of fluorescent vessel labeling and tissue clearing methods for three-dimensional visualization of vasculature

SIGNIFICANCE

Visualization of intact vasculatures is crucial to understanding the pathogeneses of different neurological and vascular diseases. Although various fluorescent vessel labeling methods have been used in combination with tissue clearing for three-dimensional (3D) visualization of different vascular networks, little has been done to quantify the labeling effect of each vessel labeling routine, as well as their applicability alongside various clearing protocols, making it difficult to select an optimal combination for finely constructing different vasculatures. Therefore, it is necessary to systematically assess the overall performance of these common vessel labeling methods combined with different tissue-clearing protocols.

AIM

A comprehensive evaluation of the labeling quality of various vessel labeling routines in different organs, as well as their applicability alongside various clearing protocols, were performed to find the optimal combinations for 3D reconstruction of vascular networks with high quality.

APPROACH

Four commonly-used vessel labeling techniques and six typical tissue optical clearing approaches were selected as candidates for the systematic evaluation.

RESULTS

The vessel labeling efficiency, vessel labeling patterns, and compatibility of each vessel labeling method with different tissue-clearing protocols were quantitatively evaluated and compared. Based on the comprehensive evaluation results, the optimal combinations were selected for 3D reconstructions of vascular networks in several organs, including mouse brain, liver, and kidney.

CONCLUSIONS

This study provides valuable insight on selecting the proper pipelines for 3D visualization of vascular networks, which may facilitate understanding of the underlying mechanisms of various neurovascular diseases.

Imaging Technologies for Cerebral Pharmacokinetic Studies: Progress and Perspectives

Pharmacokinetic assessment of drug disposition processes in vivo is critical in predicting pharmacodynamics and toxicology to reduce the risk of inappropriate drug development. The blood–brain barrier (BBB), a special physiological structure in brain tissue, hinders the entry of targeted drugs into the central nervous system (CNS), making the drug concentrations in target tissue correlate poorly with the blood drug concentrations. Additionally, once non-CNS drugs act directly on the fragile and important brain tissue, they may produce extra-therapeutic effects that may impair CNS function. Thus, an intracerebral pharmacokinetic study was developed to reflect the disposition and course of action of drugs following intracerebral absorption. Through an increasing understanding of the fine structure in the brain and the rapid development of analytical techniques, cerebral pharmacokinetic techniques have developed into non-invasive imaging techniques. Through non-invasive imaging techniques, molecules can be tracked and visualized in the entire BBB, visualizing how they enter the BBB, allowing quantitative tools to be combined with the imaging system to derive reliable pharmacokinetic profiles. The advent of imaging-based pharmacokinetic techniques in the brain has made the field of intracerebral pharmacokinetics more complete and reliable, paving the way for elucidating the dynamics of drug action in the brain and predicting its course. The paper reviews the development and application of imaging technologies for cerebral pharmacokinetic study, represented by optical imaging, radiographic autoradiography, radionuclide imaging and mass spectrometry imaging, and objectively evaluates the advantages and limitations of these methods for predicting the pharmacodynamic and toxic effects of drugs in brain tissues.

A Renal-Clearable PEGylated Semiconducting Oligomer for the NIR-II Fluorescence Imaging of Tumor

Second near-infrared window fluorescence imaging (NIR-II FI) has attracted tremendous attention in bioimaging. Until now, most probes for NIR-II FI are nanomaterials that are metabolized via hepatobiliary metabolism. Such a metabolic pathway may take several months, causing long-term toxicity. Herein, we design and synthesize a renal-clearable PEGylated semiconducting oligomer (PSO) for the NIR-II FI of tumor. PSO is composed of a semiconducting oligomer (SO) backbone as an NIR-II fluorescence reporter and four poly(ethylene glycol) (PEG) side chains as water-soluble enhancers. PSO can emit an NIR-II fluorescence signal with the maximum emission at 1000 nm under the excitation of 808 nm light. PSO shows good biocompatibility and can be partially cleared out of body via renal clearance. PSO can be utilized for the NIR-II FI of tumor as it can effectively accumulate into tumor.

Light-sheet mesoscopy with the Mesolens provides fast sub-cellular resolution imaging throughout large tissue volumes

Rapid imaging of large biological tissue specimens such as ultrathick sections of mouse brain cannot easily be performed with a standard microscope. Optical mesoscopy offers a solution, but thus far imaging has been too slow to be useful for routine use. We have developed two different illuminators for light-sheet mesoscopy with the Mesolens and we demonstrate their use in high-speed optical mesoscale imaging of large tissue specimens. The first light-sheet approach uses Gaussian optics and is straightforward to implement. It provides excellent lateral resolution and high-speed imaging, but the axial resolution is poor. The second light-sheet is a more complex Airy light-sheet that provides sub-cellular resolution in three dimensions that is comparable in quality to point-scanning confocal mesoscopy, but the light-sheet method of illuminating the specimen reduces the imaging time by a factor of 14. This creates new possibilities for high-content, higher-throughput optical bioimaging at the mesoscale.

Multichannel stimulation module as a tool for animal studies on cortical neural prostheses

Intracortical microstimulation to the visual cortex is thought to be a feasible technique for inducing localized phosphenes in patients with acquired blindness, and thereby for visual prosthesis. In order to design effective stimuli for the prosthesis, it is important to elucidate relationships between the spatio-temporal patterns of stimuli and the resulting neural responses and phosphenes through pre-clinical animal studies. However, the physiological basis of effective spatial patterns of the stimuli for the prosthesis has been little investigated in the literature, at least partly because that the previously developed multi-channel stimulation systems were designed specifically for the clinical use. In the present, a 64-channel stimulation module was developed as a scalable tool for animal experiments. The operations of the module were verified by not only dry-bench tests but also physiological animal experiments in vivo. The results demonstrated its usefulness for examining the stimulus-response relationships in a quantitative manner, and for inducing the multi-site neural excitations with a multi-electrode array. In addition, this stimulation module could be used to generate spatially patterned stimuli with up to 4,096 channels in a dynamic way, in which the stimulus patterns can be updated at a certain frame rate in accordance with the incoming visual scene. The present study demonstrated that our stimulation module is applicable to the physiological and other future studies in animals on the cortical prostheses.

Cocaine's cerebrovascular vasoconstriction is associated with astrocytic Ca2+ increase in mice

Human and animal studies have reported widespread reductions in cerebral blood flow associated with chronic cocaine exposures. However, the molecular and cellular mechanisms underlying cerebral blood flow reductions are not well understood. Here, by combining a multimodal imaging platform with a genetically encoded calcium indicator, we simultaneously measured the effects of acute cocaine on neuronal and astrocytic activity, tissue oxygenation, hemodynamics and vascular diameter changes in the mouse cerebral cortex. Our results showed that cocaine constricted blood vessels (measured by vessel diameter Φ changes), decreasing cerebral total blood volume (HbT) and temporally reducing tissue oxygenation. Cellular imaging showed that the mean astrocytic Ca2+ dependent fluorescence [Formula: see text] increase in response to cocaine was weaker but longer lasting than the mean neuronal Ca2+ dependent fluorescence [Formula: see text] changes. Interestingly, while cocaine-induced [Formula: see text] increase was temporally correlated with tissue oxygenation change, the [Formula: see text] elevation after cocaine was in temporal correspondence with the long-lasting decrease in arterial blood volumes. To determine whether the temporal association between astrocytic activation and cocaine induced vasoconstriction reflected a causal association we inhibited astrocytic Ca2+ using GFAP-DREADD(Gi). Inhibition of astrocytes attenuated the vasoconstriction resulting from cocaine, providing evidence that astrocytes play a critical role in cocaine's vasoconstrictive effects in the brain. These results indicate that neurons and astrocytes play different roles in mediating neurovascular coupling in response to cocaine. Our findings implicate neuronal activation as the main driver of the short-lasting reduction in tissue oxygenation and astrocyte long-lasting activation as the driver of the persistent vasoconstriction with cocaine. Understanding the cellular and vascular interaction induced by cocaine will be helpful for future putative treatments to reduce cerebrovascular pathology from cocaine use.

Tracking the binding of multi-functional fluorescent tags for Alzheimer's disease using quantitative multiphoton microscopy

A recent theranostic approach to address Alzheimer's disease (AD) utilizes multifunctional targets that both tag and negate the toxicity of AD biomarkers. These compounds, which emit fluorescence with both an activation and a spectral shift in the presence of Aβ, were previously characterized with traditional fluorescence imaging for binary characterization. However, these multifunctional compounds have broad and dynamic emission spectra that are dependent on factors such as the local environment, presence of Aβ deposits, etc. Since quantitative multiphoton microscopy is sensitive to the binding dynamics of molecules, we characterized the performance of two such compounds, LS-4 and ZY-12-OMe, using Simultaneous Label-free Autofluorescence Multi-harmonic (SLAM) microscopy and Fast Optical Coherence, Autofluorescence Lifetime imaging and Second harmonic generation (FOCALS) microscopy. This study shows that the combination of quantitative multiphoton imaging with multifunctional tags for AD offers new insights into the interaction of these tags with AD biomarkers and the theranostic mechanisms.

The Role of Optical Imaging in Translational Nanomedicine

Nanomedicines have been a major research focus in the past two decades and are increasingly emerging in a broad range of clinical applications. However, a proper understanding of their biodistribution is required to further progress the field of nanomedicine. For this, imaging methods to monitor the delivery and therapeutic efficacy of nanoparticles are urgently needed. At present, optical imaging is the most common method used to study the biodistribution of nanomaterials, where the unique properties of nanomaterials and advances in optical imaging can jointly result in novel methods for optimal monitoring of nanomaterials in preclinical animal models. This review article aims to give an introduction to nanomedicines and their translational impact to highlight the potential of optical imaging to study the biodistribution of nanoparticles and to monitor the delivery and therapeutic efficacy at the preclinical level. After introducing both domains, the review focuses on different techniques that can be used to overcome some intrinsic limitations of optical imaging and how this can specifically benefit nanoparticle studies. Finally, we point out some important key features of nanoparticles that currently hinder their full potential in the clinic and how the advances in optical imaging can help to provide us with the information needed to further boost the clinical translation and expand the field of nanomedicines.

Bimodal Imaging of Tumors via Genetically Engineered Escherichia coli

Although there are emerging innovations of molecular imaging probes to detect and image tumors, most of these molecular dyes and nanoparticles have limitations of low targetability in tumors and fast clearance when administered systemically. In contrast, some bacteria, such as Escherichia coli MG1655, can selectively proliferate in a hypoxic environment inside of a tumor for several days, which highlights the potential for the development of a genetically encoded multimodal imaging probe to monitor the progress of the tumor. Here, we developed bimodal imaging tumor-homing bacteria (GVs-miRFP680 MG1655) that allow both optical and acoustic imaging in tumor-bearing mice. An in vivo optical image system and a Vevo 2100 imaging system were applied to detect different imaging properties of the engineered bacteria in vivo. Our results show that the GVs-miRFP680 MG1655 bacteria can effectively integrate the advantages of low tissue absorbance from near-infrared fluorescent proteins and non-invasiveness from gas vesicles. We successfully developed GVs-miRFP680 MG1655 bacteria, which have both acoustic and optical imaging abilities in vitro and in vivo. The acoustic signal can last for up to 25 min, while the near-infrared fluorescence signal can last for up to 96 h. The combination of different imaging modalities in the tumor-homing bacteria may contribute to the non-invasive monitoring of the therapeutic effect of bacterial therapy in the future.

Design and Validation of a Handheld Optical Polarization Imager for Preoperative Delineation of Basal Cell Carcinoma

Simple Summary

Skin cancer is the most common malignancy in humans. The goal of this study was to design, implement, and clinically test a novel handheld optical polarization imaging (OPI) system for rapid and noninvasive detection of basal cell carcinoma (BCC) margins. The device is compact, lightweight, and can be operated with minimal training. To validate the handheld imager, 10 subjects with biopsy-confirmed BCC were imaged prior to Mohs surgery. The optical images were processed using a spectral encoding method to increase the accuracy of the tumor boundary delineation. Preoperative margin assessment results from the OPI were compared to the surgeon’s clinical evaluation and to the gold standard of histopathology. Our findings indicate that OPI may be a valuable tool for optimizing surgical treatment of skin cancer.

Abstract

Background: Accurate removal of basal cell carcinoma (BCC) is challenging due to the subtle contrast between cancerous and normal skin. A method aiding with preoperative delineation of BCC margins would be valuable. The aim of this study was to implement and clinically validate a novel handheld optical polarization imaging (OPI) device for rapid, noninvasive, in vivo assessment of skin cancer margins. Methods: The handheld imager was designed, built, and tested. For clinical validation, 10 subjects with biopsy-confirmed BCC were imaged. Presumable cancer margins were marked by the study surgeon. The optical images were spectrally encoded to mitigate the impact of endogenous skin chromophores. The results of OPI and of the surgeon’s preoperative visual assessment were compared to clinical intraoperative histopathology. Results: As compared to the previous prototype, the handheld imager incorporates automated image processing and has 10-times shorter acquisition times. It is twice as light and provides twice as large a field of view. Clinical validation demonstrated that margin assessments using OPI were more accurate than visual assessment by the surgeon. The images were in good correlation with histology in 9 out of 10 cases. Conclusions: Handheld OPI could improve the outcomes of skin cancer treatments without impairing clinical workflows.

Mirau-based line-field confocal optical coherence tomography for three-dimensional high-resolution skin imaging

SIGNIFICANCE

Line-field confocal optical coherence tomography (LC-OCT) is a recently introduced high-resolution imaging modality based on a combination of low-coherence optical interferometry and reflectance confocal optical microscopy with line illumination and line detection. Capable of producing three-dimensional (3D) images of the skin with cellular resolution, in vivo, LC-OCT has been mainly applied in dermatology and dermo-cosmetology. The LC-OCT devices capable of acquiring 3D images reported so far are based on a Linnik interferometer using two identical microscope objectives. In this configuration, LC-OCT cannot be designed to be a very compact and light device, and the image acquisition speed is limited.

AIM

The objective of this work was to develop a more compact and lighter LC-OCT device that is capable of acquiring images faster without significant degradation of the resolution and with optimized detection sensitivity.

APPROACH

We developed an LC-OCT device based on a Mirau interferometer using a single objective. Dynamic adjustment of the camera frequency during the depth scan is implemented, using a faster camera and a more powerful light source. The reflectivity of the beam-splitter in the Mirau interferometer was optimized to maximize the detection sensitivity. A galvanometer scanner was incorporated into the device for scanning the illumination line laterally. A stack of adjacent B-scans, constituting a 3D image, can thus be acquired.

RESULTS

The device is able to acquire and display B-scans at 17 fps. 3D images with a quasi-isotropic resolution of ∼1.5 μm (1.3, 1.9, and 1.1 μm in the x , y, and z directions, respectively) over a field of 940 μm × 600 μm × 350 μm (x × y × z) can be obtained. 3D imaging of human skin at cellular resolution, in vivo, is reported.

CONCLUSIONS

The acquisition rate of the B-scans, at 17 fps, is unprecedented in LC-OCT. Compared with the conventional LC-OCT devices based on a Linnik interferometer, the reported Mirau-based LC-OCT device can acquire B-scans ∼2 times faster. With potential advantages in terms of compactness and weight, a Mirau-based device could easily be integrated into a smaller and lighter handheld probe for use by dermatologists in their daily medical practice.

Optical imaging and spectroscopy for the study of the human brain: status report

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions.

Cocaine's effects on the reactivity of the medial prefrontal cortex to ventral tegmental area stimulation: optical imaging study in mice

BACKGROUND AND AIMS

The prefrontal cortex (PFC) is modulated by dopaminergic and glutamatergic neurons that project from the ventral tegmental area (VTA) and disruption of this modulation might facilitate impulsive behaviors during cocaine intoxication. Here, we assessed the effects of acute cocaine (30 mg/kg, i.p.) on the reactivity of the PFC to VTA stimulation.

METHODS

Using a genetically encoded calcium indicator (GCaMP6f), we optically imaged the neuronal Ca2+ reactance in medial PFC (mPFC) in response to 'tonic-like' (5 Hz) and 'phasic-like' (50 Hz) electrical VTA stimulation. The high temporal and spatial resolutions of our optical system allowed us to capture single Ca2+ neuronal transients from individual stimuli with 'tonic-like' stimulation and to visualize single neuronal activation evoked by 'phasic-like' VTA stimulation.

RESULTS

'Tonic-like' VTA stimulation induced a rapid increase in mean neuronal Ca2+ in mPFC followed by a plateau and recovery upon termination of stimulation. After cocaine, the mPFC sensitivity to 'tonic-like' VTA stimulation was attenuated, with a 50.4% reduction (P = 0.03) in the number of Ca2+ transients corresponding to single electrical stimuli but the recovery time was lengthened (4.30 ± 0.25 sec to 5.41 ± 0.24 sec, P = 0.03). 'Phasic-like' stimulation evoked a rapid Ca2+ fluorescence increase in mPFC with an immediate decay process, and while cocaine did not affect the peak response (7.17 ± 1.07% versus 7.13 ± 0.96%, P = 0.98) it shortened the recovery time to baseline (3.27 ± 0.11 sec versus 2.38 ± 0.23 sec, P = 0.005).

CONCLUSIONS

Acute cocaine impairs reactivity of medial prefrontal cortex (mPFC) to ventral tegmental area stimulation, decreasing its sensitivity to 'tonic-like' stimulation and lengthening the recovery time to return to baseline while shortening it for phasic stimulation. These changes in mPFC might contribute to cocaine binging during intoxication.

Software for non-parametric image registration of 2-photon imaging data

Functional 2-photon microscopy is a key technology for imaging neuronal activity. The recorded image sequences, however, can contain non-rigid movement artifacts which requires high-accuracy movement correction. Variational optical flow (OF) estimation is a group of methods for motion analysis with established performance in many computer vision areas. However, it has yet to be adapted to the statistics of 2-photon neuroimaging data. In this work, we present the motion compensation method Flow-Registration that outperforms previous alignment tools and allows to align and reconstruct even low signal-to-noise ratio 2-photon imaging data and is able to compensate high-divergence displacements during local drug injections. The method is based on statistics of such data and integrates previous advances in variational OF estimation. Our method is available as an easy-to-use ImageJ/FIJI plugin as well as a MATLAB toolbox with modular, object oriented file IO, native multi-channel support and compatibility with existing 2-photon imaging suites.

Label-free viability assay using in-line holographic video microscopy

Total holographic characterization (THC) is presented here as an efficient, automated, label-free method of accurately identifying cell viability. THC is a single-particle characterization technology that determines the size and index of refraction of individual particles using the Lorenz-Mie theory of light scattering. Although assessment of cell viability is a challenge in many applications, including biologics manufacturing, traditional approaches often include unreliable labeling with dyes and/or time consuming methods of manually counting cells. In this work we measured the viability of Saccharomyces cerevisiae yeast in the presence of various concentrations of isopropanol as a function of time. All THC measurements were performed in the native environment of the sample with no dilution or addition of labels. Holographic measurements were made with an in-line holographic microscope using a 40[Formula: see text] objective lens with plane wave illumination. We compared our results with THC to manual counting of living and dead cells as distinguished with trypan blue dye. Our findings demonstrate that THC can effectively distinguish living and dead yeast cells by the index of refraction of individual cells.

Click-Chemistry-Based Biomimetic Ligands Efficiently Capture G-Quadruplexes In Vitro and Help Localize Them at DNA Damage Sites in Human Cells

Interrogating G-quadruplex (G4) biology at its deepest roots in human cells relies on the design, synthesis, and use of ever smarter molecular tools. Here, we demonstrate the versatility of biomimetic G4 ligands referred to as TASQ (template assembled synthetic G-quartet) in which a biotin handle was incorporated for G4-focused chemical biology investigations. We have rethought the biotinylated TASQ design to make it readily chemically accessible via an efficient click-chemistry-based strategy. The resulting biotinylated, triazole-assembled TASQ, or BioTriazoTASQ, was thus shown to efficiently isolate both DNA and RNA G4s from solution by affinity purification protocols, for identification purposes. Its versatility was then further demonstrated by optical imaging that provided unique mechanistic insights into the actual strategic relevance of G4-targeting strategies, showing that ligand-stabilized G4 sites colocalize with and, thus, are responsible for DNA damage foci in human cells.

Optical imaging detects metabolic signatures associated with oocyte quality

Oocyte developmental potential is intimately linked to metabolism. Existing approaches to measure metabolism in the cumulus oocyte complex (COC) do not provide information on the separate cumulus and oocyte compartments. Development of an assay that achieves this may lead to an accurate diagnostic for oocyte quality. Optical imaging of the autofluorescent cofactors NAD(P)H and FAD provides a spatially resolved indicator of metabolism via the optical redox ratio ($\mathrm{FAD}/\left[\mathrm{NAD}\left(\mathrm{P}\right)\mathrm{H}+\mathrm{FAD}\right]$). This may provide an assessment of oocyte quality. Here, we determined whether the optical redox ratio is a robust methodology for measuring metabolism in the cumulus and oocyte compartments compared with oxygen consumption in the whole COC. We also determined whether optical imaging could detect metabolic differences associated with poor oocyte quality (etomoxir-treated). We used confocal microscopy to measure NAD(P)H and FAD, and extracellular flux to measure oxygen consumption. We found that the optical redox ratio was an accurate reflection of metabolism in the oocyte compartment when compared with oxygen consumption (whole COC). Etomoxir-treated COCs showed significantly lower levels of NAD(P)H and FAD compared to control. While confocal imaging demonstrated the premise, we validated this approach using hyperspectral imaging, which is clinically compatible due to its low energy dose. This confirmed lower NAD(P)H and FAD in etomoxir-treated COCs. When comparing imaged vs non-imaged COCs, subsequent preimplantation development and post-transfer viability were comparable. Collectively, these results demonstrate that label-free optical imaging of metabolic cofactors is a safe and sensitive assay for measuring metabolism and has potential to assess oocyte developmental competence.

Formulation of a Thermosensitive Imaging Hydrogel for Topical Application and Rapid Visualization of Tumor Margins in the Surgical Cavity

Simple Summary

We have developed a formulation for an innovative, quenched, cathepsin-targeted, fluorescent molecular probe to enhance resection quality for several solid-tumor cancers. Unlike other formulations for imaging probes or tracers in development and entering the clinic, which require systemic administration hours before the procedure, this current formulation is applied topically into the surgical cavity immediately after a standard of care resection. Within minutes of application, the probe activates in the presence of residual cancer in the surgical wound and provides a strong fluorescent signal that precisely delineates any remaining cancer, enabling a more complete resection. Utilization of this imaging gel formulation for topical application to detect breast cancer in the surgical cavity during surgery has the potential to reduce re-excisions, with consequent savings in healthcare costs and enhancement in patient quality of life.

Abstract

Background: Tumor-positive surgical margins during primary breast cancer (BCa) surgery are associated with a two-fold increase in the risk of local recurrence when compared with tumor-negative margins. Pathological microscopic evaluation of the samples only assesses about 1/10 of 1% of the entire volume of the removed BCa specimens, leading to margin under-sampling and potential local recurrence in patients with pathologically clean margins, i.e., false negative margins. In the case of tumor-positive margins, patients need to undergo re-excision and/or radiation therapy, resulting in increases in complications, morbidity, and healthcare costs. Development of a simple real-time imaging technique to identify residual BCa in the surgical cavity rapidly and precisely could significantly improve the quality of care. Methods: A small-molecule, fluorescently quenched protease-substrate probe, AKRO-QC-ICG, was tested as part of a thermosensitive imaging gel formulated for topical application and imaging of the BCa surgical cavity. Results: More than forty formulations of gel mixtures were investigated to enable easy fluid application and subsequent solidification once applied, preventing dripping and pooling in the surgical cavity. The final formulation was tested using human BCa orthotopic implants in nude and NSG patient-derived xenografts (PDX) mice. This formulation of Pluronic F-127/DMSO/AKRO-QC-ICG imaging gel was found to be a good solvent for the probe, with a desirable thermo-reversible solid–gel transition and mechanical strength for distribution of AKRO-QC-ICG on the surfaces of tissue. It demonstrated excellent ability to detect BCa tissue after 10 min exposure, with a high signal-to-noise ratio both in mouse xenografts and freshly excised human lumpectomy tissue. The in vivo efficacy of the AKRO-QC-ICG imaging gel to detect BCa revealed the levels of sensitivity/specificity = 0.92/1 in 12 nude mice, which was corroborated with the sensitivity/specificity = 0.94/1 in 10 PDX mice. Conclusions: Utilization of Pluronic F-127/DMSO/AKRO-QC-ICG imaging gel for topical application to detect BCa in the surgical cavity during surgery has the potential to reduce re-excisions, with consequent savings in healthcare costs and enhancement in patient quality of life.

Combining magnetic resonance imaging with readout and/or perturbation of neural activity in animal models: Advantages and pitfalls

One of the main challenges in brain research is to link all aspects of brain function: on a cellular, systemic, and functional level. Multimodal neuroimaging methodology provides a continuously evolving platform. Being able to combine calcium imaging, optogenetics, electrophysiology, chemogenetics, and functional magnetic resonance imaging (fMRI) as part of the numerous efforts on brain functional mapping, we have a unique opportunity to better understand brain function. This review will focus on the developments in application of these tools within fMRI studies and highlight the challenges and choices neurosciences face when designing multimodal experiments.

Chronic co-implantation of ultraflexible neural electrodes and a cranial window

Significance: Electrophysiological recording and optical imaging are two prevalent neurotechnologies with complementary strengths, the combined application of which can significantly improve our capacity in deciphering neural circuits. Flexible electrode arrays can support longitudinal optical imaging in the same brain region, but their mechanical flexibility makes surgical preparation challenging. Here, we provide a step-by-step protocol by which an ultraflexible nanoelectronic thread is co-implanted with a cranial window in a single surgery to enable chronic, dual-modal measurements. Aim: The method uses 1 - μ m -thick polymer neural electrodes which conform to the site of implantation. The mechanical flexibility of the probe allows bending without breaking and enables long-lasting electrophysiological recordings of single-unit activities and concurrent, high-resolution optical imaging through the cranial window. Approach: The protocol describes methods and procedures to co-implant an ultraflexible electrode array and a glass cranial window in the mouse neocortex. The implantation strategy includes temporary attachment of flexible electrodes to a retractable tungsten-microwire insertion shuttle, craniotomy, stereotaxic insertion of the electrode array, skull fixation of the cranial window and electrode, and installation of a head plate. Results: The resultant implant allows simultaneous interrogation of brain activity both electrophysiologically and optically for several months. Importantly, a variety of optical imaging modalities, including wide-field fluorescent imaging, two-photon microscopy, and functional optical imaging, can be readily applied to the specific brain region where ultraflexible electrodes record from. Conclusions: The protocol describes a method for co-implantation of ultraflexible neural electrodes and a cranial window for chronic, multimodal measurements of brain activity in mice. Device preparation and surgical implantation are described in detail to guide the adaptation of these methods for other flexible neural implants and cranial windows.

Spatiotemporal patterns of spontaneous brain activity: a mini-review

The brain exists in a state of constant activity in the absence of any external sensory input. The spatiotemporal patterns of this spontaneous brain activity have been studied using various recording and imaging techniques. This has enabled considerable progress to be made in elucidating the cellular and network mechanisms that are involved in the observed spatiotemporal dynamics. This mini-review outlines different spatiotemporal dynamic patterns that have been identified in four commonly used modalities: electrophysiological recordings, optical imaging, functional magnetic resonance imaging, and electroencephalography. Signal sources for each modality, possible sources of the observed dynamics, and future directions are also discussed.

Reporter Transgenes for Monitoring the Antitumor Efficacy of Recombinant Oncolytic Viruses

Accurate measurement of tumor size and margins is crucial for successful oncotherapy. In the last decade, non-invasive imaging modalities, including optical imaging using non-radioactive substrates, deep-tissue imaging with radioactive substrates, and magnetic resonance imaging have been developed. Reporter genes play the most important role among visualization tools; their expression in tumors and metastases makes it possible to track changes in the tumor growth and gauge therapy effectiveness. Oncolytic viruses are often chosen as a vector for delivering reporter genes into tumor cells, since oncolytic viruses are tumor-specific, meaning that they infect and lyse tumor cells without damaging normal cells. The choice of reporter transgenes for genetic modification of oncolytic viruses depends on the study objectives and imaging methods used. Optical imaging techniques are suitable for in vitro studies and small animal models, while deep-tissue imaging techniques are used to evaluate virotherapy in large animals and humans. For optical imaging, transgenes of fluorescent proteins, luciferases, and tyrosinases are used; for deep-tissue imaging, the most promising transgene is the sodium/iodide symporter (NIS), which ensures an accumulation of radioactive isotopes in virus-infected tumor cells. Currently, NIS is the only reporter transgene that has been shown to be effective in monitoring tumor virotherapy not only in preclinical but also in clinical studies.

Molecular imaging in oncology: Current impact and future directions

The authors define molecular imaging, according to the Society of Nuclear Medicine and Molecular Imaging, as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Although practiced for many years clinically in nuclear medicine, expansion to other imaging modalities began roughly 25 years ago and has accelerated since. That acceleration derives from the continual appearance of new and highly relevant animal models of human disease, increasingly sensitive imaging devices, high-throughput methods to discover and optimize affinity agents to key cellular targets, new ways to manipulate genetic material, and expanded use of cloud computing. Greater interest by scientists in allied fields, such as chemistry, biomedical engineering, and immunology, as well as increased attention by the pharmaceutical industry, have likewise contributed to the boom in activity in recent years. Whereas researchers and clinicians have applied molecular imaging to a variety of physiologic processes and disease states, here, the authors focus on oncology, arguably where it has made its greatest impact. The main purpose of imaging in oncology is early detection to enable interception if not prevention of full-blown disease, such as the appearance of metastases. Because biochemical changes occur before changes in anatomy, molecular imaging-particularly when combined with liquid biopsy for screening purposes-promises especially early localization of disease for optimum management. Here, the authors introduce the ways and indications in which molecular imaging can be undertaken, the tools used and under development, and near-term challenges and opportunities in oncology.