What Fechner could not do: Separating perceptual encoding and decoding with difference scaling.

A key question in perception research is how stimulus variations translate into perceptual magnitudes, that is, the perceptual encoding process. As experimenters, we cannot probe perceptual magnitudes directly, but infer the encoding process from responses obtained in a psychophysical experiment. The most prominent experimental technique to measure perceptual appearance is matching, where observers adjust a probe stimulus to match a target in its appearance along the dimension of interest. The resulting data quantify the perceived magnitude of the target in physical units of the probe, and are thus an indirect expression of the underlying encoding process. In this paper, we show analytically and in simulation that data from matching tasks do not sufficiently constrain perceptual encoding functions, because there exist an infinite number of pairs of encoding functions that generate the same matching data. We use simulation to demonstrate that maximum likelihood conjoint measurement (Ho, Landy, & Maloney, 2008; Knoblauch & Maloney, 2012) does an excellent job of recovering the shape of ground truth encoding functions from data that were generated with these very functions. Finally, we measure perceptual scales and matching data for White's effect (White, 1979) and show that the matching data can be predicted from the estimated encoding functions, down to individual differences.

Ordinal Characterization of Similarity Judgments.

Characterizing judgments of similarity within a perceptual or semantic domain, and making inferences about the underlying structure of this domain from these judgments, has an increasingly important role in cognitive and systems neuroscience. We present a new framework for this purpose that makes very limited assumptions about how perceptual distances are converted into similarity judgments. The approach starts from a dataset of empirical judgments of relative similarities: the fraction of times that a subject chooses one of two comparison stimuli to be more similar to a reference stimulus. These empirical judgments provide Bayesian estimates of underling choice probabilities. From these estimates, we derive three indices that characterize the set of judgments, measuring consistency with a symmetric dis-similarity, consistency with an ultrametric space, and consistency with an additive tree. We illustrate this approach with example psychophysical datasets of dis-similarity judgments in several visual domains and provide code that implements the analyses.

Trayectorias de la enseñanza de las matemáticas en ingeniería: entornos colombiano y norteamericano

RE S U M E N Este texto presenta una revisión sistemática de artículos científicos, tipo scoping review, sobre educación matemática en programas de ingeniería, en los entornos colombiano y norteamericano, durante el periodo 2000 - 2020. La exploración, surgida del proyecto de investigación "Fundamentos teóricos y metodológicos de la enseñanza de la matemática en ingeniería", siguió los protocolos del Instituto Joanna Briggs y consideró literatura especializada incluida en Scopus y Publindex. La información, clasificada como "experiencia pedagógica", "reflexión" o "revisión", permitió describir tendencias de investigación y acción respecto a la enseñanza, el aprendizaje, el currículo y la evaluación de las matemáticas en ingeniería. Los resultados permitieron concluir que en el contexto norteamericano existe un interés significativo por la investigación sobre el aprendizaje, el currículo y la evaluación de las matemáticas en ingeniería, desde enfoques sistêmicos, interdisciplinarios y socioculturales. En contraste, la literatura sobre el tema en Colombia presenta una tendencia al estudio de procesos de enseñanza, desde perspectivas disciplinares y cognitivas de la educación matemática.

This paper presents a systematic review of scientific articles, scoping review type, on mathematics education in engineering programs, in the Colombian and North American environments, during the period 2000 - 2020. The exploration, which arose from the research project "Theoretical and methodological foundations of mathematics education in engineering", followed the protocols of the Joanna Briggs Institute and considered specialized literature included in Scopus and Publindex. The information, classified as "pedagogical experience", "reflection" or "review", allowed describing research and action trends regarding teaching, learning, curriculum and assessment of engineering mathematics. The results allowed concluding that in the North American context there is a significant interest in research on learning, curriculum and assessment of engineering mathematics, from systemic, interdisciplinary and sociocultural approaches. In contrast, the literature on the subject in Colombia presents a tendency to study teaching processes from disciplinary and cognitive perspectives of mathematics education.

Este texto apresenta uma revisão sistemática de artigos científicos, tipo revisão de escopo, sobre educação matemática em programas de engenharia, nos ambientes colombiano e norte-americano, durante o período de 2000 a 2020. A exploração, decorrente do projeto de pesquisa "Fundamentos teóricos e metodológicos da educação matemática em engenharia", seguiu os protocolos do Instituto Joanna Briggs e considerou literatura especializada incluída no Scopus e no Publindex. As informações, classificadas como "experiência pedagógica", "reflexão" ou "revisão", permitiram descrever as tendências de pesquisa e ação em relação ao ensino, aprendizagem, currículo e avaliação da matemática de engenharia. Os resultados levaram à conclusão de que no contexto norte-americano há um interesse significativo na pesquisa sobre aprendizagem, currículo e avaliação de matemática de engenharia a partir de abordagens sistêmicas, interdisciplinares e socioculturais. Em contraste, a literatura sobre o assunto na Colômbia mostra uma tendência a estudar os processos de ensino a partir de perspectivas disciplinares e cognitivas da educação matemática.

Evaluación de los retrasos en actividades de construcción utilizando redes Bayesianas: Caso de estudio / Delay assessment of construction site activities using Bayesian networks: Case study / Avaliação dos atrasos nas atividades de construção utilizando redes Bayesianas: Estudo de caso

RESUMEN Los retrasos en proyectos de construcción son atribuídos a la concurrencia de factores que afectan el buen desarrollo, y mitigarlos, constituye uno de los mayores desafios que afronta la industria, ya que requiere tener en cuenta la dependencia e incidencia integrada de ellos. El objetivo de este estudio fue evaluar la influencia de factores de retraso sobre la duración de actividades de construcción, a través de un método que emplee las redes Bayesianas. Siguiendo la metodologia de investigación basada en el diseno, y aplicando un caso de estudio, se propone un método que incluye cómo identificar los principales factores de retraso que afecten las actividades; cómo representar la influencia y dependencia de estos factores por medio de una red Bayesiana; y cómo estimar el nivel de influencia por medio de la simulación de la red. Los resultados de esta investigación muestran como la aplicación de una red Bayesiana se puede emplear como apoyo a los profesionales de obra para gestionar las actividades de construcción y tomar decisiones en la medida que se actualice la información de la red bayesiana.

ABSTRACT The concurrence of multiple factors adversely affects construction project performance, resulting in delays. Mitigating such factors is challenging for the industry because solutions must include dependence and influence. Hence, managers must consider their systemic and integrated influence on the construction process for tracking projects. This study aimed to evaluate the influence of delay factors on the duration of construction site activities using Bayesian network techniques. Based on the design-based research methodology and the application in a case study this study proposed a method that involves three steps. First, identifying the main delay factors affecting construction activities; second, designing an influencing model as a Bayesian network; and third, estimating the integrated influence of such factors by simulating the Bayesian network. The results showed how a Bayesian network could support the construction team in managing the construction-site activities and making decisions about the performance of the construction process.

RESUMO Atrasos nos projetos de construção são atribuídos à concorrência de múltiplos fatores que afetam o desenvolvimento adequado do projeto, e mitigá-los é um dos maiores desafios enfrentados pelo setor; pois requer levar em conta a incidência integrada dos mesmos. O objetivo deste estudo foi avaliar a influência de um grupo de fatores sobre a duração das atividades de construção, utilizando a técnica da rede Bayesiana. Seguindo a metodologia de pesquisa baseada em projeto, foram identificados os principais fatores de atraso que afetam as atividades de construção e as relações de causa e efeito foram modeladas para estimar sua influência sobre a duração das atividades de fundação de um projeto de construção. Os resultados desta pesquisa mostram como a aplicação de uma rede Bayesiana pode ser usada para apoiar os profissionais do local no gerenciamento das atividades de construção e na tomada de decisões relativas ao desenvolvimento do projeto, considerando a incerteza e os fatores que influenciam o desenvolvimento do projeto.

The effect of scalable PDMS gas-entrapping microstructures on the dynamics of a single cavitation bubble.

The effect of gas-entrapping polydimethylsiloxane (PDMS) microstructures on the dynamics of cavitation bubbles laser-induced next to the PDMS surface is investigated and compared against the cavitation dynamics next to a flat smooth boundary. Local pressure gradients produced by a cavitation bubble cause the air pockets entrapped in the PDMS microstructures to expand and oscillate, leading to a repulsion of the cavitation bubble. The microstructures were fabricated as boxed crevices via a simple and scalable laser ablation technique on cast acrylic, allowing for testing of variable structure sizes and reusable molds. The bubble dynamics were observed using high speed photography and the surrounding flows were visualized and quantified using particle tracking velocimetry. Smaller entrapped air pockets showed an enhanced ability to withstand deactivation at three stand-off distances and over 50 subsequent cavitation events. This investigation provides insight into the potential to direct the collapse of a cavitation bubble away from a surface to mitigate erosion or to enhance microfluidic mixing in low Reynolds number flows.

Photothermal heating of titanium nitride nanomaterials for fast and uniform laser warming of cryopreserved biomaterials.

Titanium nitride (TiN) is presented as an alternative plasmonic nanomaterial to the commonly used gold (Au) for its potential use in laser rewarming of cryopreserved biomaterials. The rewarming of vitrified, glass like state, cryopreserved biomaterials is a delicate process as potential ice formation leads to mechanical stress and cracking on a macroscale, and damage to cell walls and DNA on a microscale, ultimately leading to the destruction of the biomaterial. The use of plasmonic nanomaterials dispersed in cryoprotective agent solutions to rapidly convert optical radiation into heat, generally supplied by a focused laser beam, proposes a novel approach to overcome this difficulty. This study focuses on the performance of TiN nanoparticles (NPs), since they present high thermal stability and are inexpensive compared to Au. To uniformly warm up the nanomaterial solutions, a beam splitting laser system was developed to heat samples from multiple sides with equal beam energy distribution. In addition, uniform laser warming requires equal distribution of absorption and scattering properties in the nanomaterials. Preliminary results demonstrated higher absorption but less scattering in TiN NPs than Au nanorods (GNRs). This led to the development of TiN clusters, synthetized by nanoparticle agglomeration, to increase the scattering cross-section of the material. Overall, this study analyzed the heating rate, thermal efficiency, and heating uniformity of TiN NPs and clusters in comparison to GNRs at different solution concentrations. TiN NPs and clusters demonstrated higher heating rates and solution temperatures, while only clusters led to a significantly improved uniformity in heating. These results highlight a promising alternative plasmonic nanomaterial to rewarm cryopreserved biological systems in the future.

Nanocrystalline Yttria-Stabilized Zirconia Ceramics for Cranial Window Applications.

Transparent yttria-stabilized zirconia (YSZ) ceramics are promising for cranial window applications because of their good mechanical and optical properties as well as biocompatibility. YSZ discs with different yttria concentrations were either processed via current-activated pressure-assisted densification (CAPAD) using commercial nanoparticles or densified via spark plasma sintering (SPS) using pyrolysis-synthesized nanoparticles in-house. This study provided critical results to screen composition, processing, microstructure, and cytocompatibility of transparent YSZ discs for cranial window applications. CAPAD-processed YSZ discs with 6 or 8 mol % yttria (6YSZ and 8YSZ) and SPS-densified YSZ discs with 4 mol % yttria (4YSZ_P) showed 200-350 nm polycrystalline grains containing 20-30 nm crystallite domains. SPS-densified YSZ discs with 8 mol % yttria (8YSZ_P) showed larger polycrystalline grains of 819 ± 155 nm with 29 ± 5 nm crystallite domains. CAPAD-processed YSZ discs with 3 mol % yttria (3YSZ) showed 39 ± 9 nm grains. Bone-marrow-derived stem cells (BMSCs) on the polished YSZ discs showed statistically higher spreading areas than those on the unpolished YSZ discs of the same compositions. Generally, polished 8YSZ, 4YSZ_P, and 8YSZ_P discs and unpolished 8YSZ_R, 4YSZ_PR, and 8YSZ_PR discs had lower average cell adhesion densities than other YSZ discs under direct contact conditions. Under indirect contact conditions, all the YSZ disc groups showed similar average cell adhesion densities to the Cell-only control. The groups of polished 4YSZ_P and 8YSZ_P discs, unpolished 4YSZ_PR and 8YSZ_PR discs, and particle control of 8YSZ_Pnp showed higher Y3+ ion concentrations than other groups. No mineral deposition was detected on the polished YSZ discs after cell culture. Considering multiple factors such as cytocompatibility, cell adhesion density, Y3+ ion release, mineral deposition, and optical transparency collectively, 8YSZ may be the best candidate for the cranial window applications. Further studies are needed to evaluate the long-term transparency and biocompatibility of YSZ discs.

Experimental and computational model approach to assess the photothermal effects in transparent nanocrystalline yttria stabilized zirconia cranial implant.

BACKGROUND AND OBJECTIVE: In the last few years, we have been exploring the use of transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) ceramics as a biomedical transparent cranial implant, referred as the "Window to the Brain" (WttB). The WttB aims at providing chronical optical access to the brain for diagnostics and therapeutic procedures and it has shown to provide an effective means to obtain enhanced results from optical imaging techniques. The objective of this work is to explore the photothermal effects of the Wttb produced when it is irradiated by a laser source. METHODS: We make experimental and computer models. The thermal effects of laser irradiation on the nc-YSZ samples were evaluated upon registering the induced temperature changes by means of thermal imaging. The computer models try to mimic the experimental models using a similar geometry, reproducing the physical situation by a couple thermal-optical problem and adjusting the main parameters from the experimental results. RESULTS: Experimental and computational coincides in results: Temperatures at the bottom surface of the implant does not exceed those which produce thermal damage. The quantitative comparison between experimental and computational models show that differences in results are under a reasonable value of 5% and qualitatively we observe a similar behavior. The results provide optimum values for the thermal-optical nc-YSZ parameters considering a linear and exponential relationship with temperature for the absorption coefficient: The thermal conductivity is k = 2.13 W/m·K and the absorption coefficient α varies from 426 to 526 m-1 with the linear relationship, and k = 2.04 W/m·K and α ∈ [433,502] m-1 with the exponential. The reflection coefficient is R = 19% in both cases. CONCLUSIONS: The temperatures achieved in the nc-YSZ during the laser irradiation are suitable for biomedical applications. The combination of experimental and computational models contributes to build a clinically oriented model with the thermal-optical parameters values stablished and to determine their influence in results. Specifically, the absorption coefficient of the nc-YSZ samples is the most influent parameter in the obtained temperatures. Moreover, this combination provides a method to evaluate the relevant thermal-optical parameters of nc-YSZ samples obtained with different manufacturing processes.

Conjoint measurement of perceived transparency and perceived contrast in variegated checkerboards.

One fundamental question in vision research is how the retinal input is segmented into perceptually relevant variables. A striking example of this segmentation process is transparency perception, in which luminance information in one location contributes to two perceptual variables: the properties of the transparent medium itself and of what is being seen in the background. Previous work by Robilotto et al. (2002, 2004) suggested that perceived transparency is closely related to perceived contrast, but how these two relate to retinal luminance has not been established. Here we studied the relationship between perceived transparency, perceived contrast, and image luminance using maximum likelihood conjoint measurement (MLCM). Stimuli were rendered images of variegated checkerboards that were composed of multiple reflectances and partially covered by a transparent overlay. We systematically varied the transmittance and reflectance of the transparent medium and measured perceptual scales of perceived transparency. We also measured scales of perceived contrast using cut-outs of the transparency stimuli that did not contain any geometrical cues to transparency. Perceptual scales for perceived transparency and contrast followed a remarkably similar pattern across observers. We tested the empirically observed scales against predictions from various contrast metrics and found that perceived transparency and perceived contrast were equally well predicted by a metric based on the logarithm of Michelson or Whittle contrast. We conclude that judgments of perceived transparency and perceived contrast are likely to be supported by a common mechanism, which can be computationally captured as a logarithmic contrast.

Laser-induced cavitation in plasmonic nanoparticle solutions: A comparative study between gold and titanium nitride.

In this work, we present an extensive comparative study between novel titanium nitride nanoparticles (TiN NPs) and commercial gold nanorods (GNR), both dispersed in water and exposed to a pulsed laser-induced cavitation process. The optical density, shockwave emission, and bubble formation of these solutions were investigated using shadowgraphy, spatial transmittance modulation, and acoustic measurements. TiN nanoparticle solutions exhibited high stability undser a periodic nanosecond pulsed-laser irradiation, making these nanomaterials promising agents for high-power applications. In addition, they demonstrated a stronger nonlinear absorption compared to the GNR solutions, and plasma formation at lower laser energies. This study advances our understanding of the optical properties of TiN and discusses significant differences compared to gold, with important implications for future applications of this material in water treatment, nonlinear signal converting, and laser-induced cavitation for medical implementations, among others.

Group Refractive Index of Nanocrystalline Yttria-Stabilized Zirconia Transparent Cranial Implants.

Transparent "Window to the Brain" (WttB) cranial implants made from a biocompatible ceramic, nanocrystalline Yttria-Stabilized Zirconia (nc-YSZ), were recently reported. These reports demonstrated chronic brain imaging across the implants in mice using optical coherence tomography (OCT) and laser speckle imaging. However, optical properties of these transparent cranial implants are neither completely characterized nor completely understood. In this study, we measure optical properties of the implant using a swept source OCT system with a spectral range of 136 nm centered at 1,300 nm to characterize the group refractive index of the nc-YSZ window, over a narrow range of temperatures at which the implant may be used during imaging or therapy (20-43°C). Group refractive index was found to be 2.1-2.2 for OCT imaging over this temperature range. Chromatic dispersion for this spectral range was observed to vary over the sample, sometimes flipping signs between normal and anomalous dispersion. These properties of nc-YSZ should be considered when designing optical systems and procedures that propagate light through the window, and when interpreting OCT brain images acquired across the window.

Medically Attended Outpatient Coronavirus Infections in Ecuadorean Children During the 20 Months Preceding Countrywide Lockdown Related to the SARS-CoV-2 Pandemic of 2020.

BACKGROUND: Human coronaviruses (HCoVs) cause respiratory tract infections during childhood manifesting as common colds, bronchiolitis, croup and pneumonia. In temperate geographies, HCoV activity peaks between December and March. The epidemiology and manifestations of HCoV infections have not been previously reported from Ecuador. METHODS: Children <5 years who presented with ≥2 symptoms consistent with an acute respiratory tract infection were eligible for enrollment. After obtaining informed consent, demographic data and details regarding the acute illness were recorded. Secretions collected with a nasopharyngeal swab underwent diagnostic testing using multiplex polymerase chain reaction. RESULTS: A total of 850 subjects were enrolled. A total of 677 (80%) tested positive for at least 1 pathogen, including 49 (7.2%) who tested positive for ≥1 HCoV type. HCoV-NL63 was the most frequent type detected (39%), followed by HCoV-OC43 (27%), 229E (22%) and HKU1 (12%). Nearly all subjects who tested positive for HCoV had nasal congestion or secretions (47/49; 96%). The most frequent syndromic diagnosis was common cold (41%), followed by bronchiolitis (27%). We found no association between the infecting HCoV type and subject's syndromic diagnosis (P > 0.05) or anatomic location of infection (upper vs. lower respiratory tract; P > 0.05). The 2018-2019 peak HCoV activity occurred from October to November; the 2019-2020 peak occurred from January to February. CONCLUSIONS: HCoVs were detected in ~7% of outpatient Ecuadorean children <5 years of age with symptoms of acute respiratory tract infection. The most frequently detected HCoV types, and the period of peak HCoV activity differed for the 2018-2019 and 2019-2020 seasons.

Chronic Brain Imaging Across a Transparent Nanocrystalline Yttria-Stabilized-Zirconia Cranial Implant.

Repeated non-diffuse optical imaging of the brain is difficult. This is due to the fact that the cranial bone is highly scattering and thus a strong optical barrier. Repeated craniotomies increase the risk of complications and may disrupt the biological systems being imaged. We previously introduced a potential solution in the form of a transparent ceramic cranial implant called the Window to the Brain (WttB) implant. This implant is made of nanocrystalline Yttria-Stabilized Zirconia (nc-YSZ), which possesses the requisite mechanical strength to serve as a permanent optical access window in human patients. In this present study, we demonstrate repeated brain imaging of n = 5 mice using both OCT and LSI across the WttB implant over 4 weeks. The main objectives are to determine if the WttB implant allows for chronic OCT imaging, and to shed further light on the question of whether optical access provided by the WttB implant remains stable over this duration in the body. The Window to the Brain implant allowed for stable repeated imaging of the mouse brain with Optical Coherence Tomography over 28 days, without loss of signal intensity. Repeated Laser Speckle Imaging was also possible over this timeframe, but signal to noise ratio and the sharpness of vessels in the images decreased with time. This can be partially explained by elevated blood flow during the first imaging session in response to trauma from the surgery, which was also detected by OCT flow imaging. These results are promising for long-term optical access through the WttB implant, making feasible chronic in vivo studies in multiple neurological models of brain disease.

Toward reliable measurements of perceptual scales in multiple contexts.

A central question in psychophysical research is how perceptual differences between stimuli translate into physical differences and vice versa. Characterizing such a psychophysical scale would reveal how a stimulus is converted into a perceptual event, particularly under changes in viewing conditions (e.g., illumination). Various methods exist to derive perceptual scales, but in practice, scale estimation is often bypassed by assessing appearance matches. Matches, however, only reflect the underlying perceptual scales but do not reveal them directly. Two recently developed methods, MLDS (Maximum Likelihood Difference Scaling) and MLCM (Maximum Likelihood Conjoint Measurement), promise to reliably estimate perceptual scales. Here we compared both methods in their ability to estimate perceptual scales across context changes in the domain of lightness perception. In simulations, we adopted a lightness constant, a contrast, and a luminance-based observer model to generate differential patterns of perceptual scales. MLCM correctly recovered all models. MLDS correctly recovered only the lightness constant observer model. We also empirically probed both methods with two types of stimuli: (a) variegated checkerboards that support lightness constancy and (b) center-surround stimuli that do not support lightness constancy. Consistent with the simulations, MLDS and MLCM provided similar scale estimates in the first case and divergent estimates in the second. In addition, scales from MLCM-and not from MLDS-accurately predicted asymmetric matches for both types of stimuli. Taking experimental and simulation results together, MLCM seems more apt to provide a valid estimate of the perceptual scales underlying judgments of lightness across viewing conditions.

Characterization of ageing resistant transparent nanocrystalline yttria-stabilized zirconia implants.

The "Window to the Brain" is a transparent cranial implant under development, based on nanocrystalline yttria-stabilized zirconia (nc-YSZ) transparent ceramic material. Previous work has demonstrated the feasibility of this material to facilitate brain imaging over time, but the long-term stability of the material over decades in the body is unknown. In this study, the low-temperature degradation (LTD) of nc-YSZ of 3, 6, and 8 mol % yttria is compared before and after accelerated ageing treatments following ISO standards for assessing the ageing resistance of zirconia ceramics. After 100 hr of accelerated ageing (equivalent to many decades of ageing in the body), the samples do not show any signs of phase transformation to monoclinic by X-ray diffraction and micro-Raman spectroscopy. Moreover, the mechanical hardness of the samples did not decrease, and changes in optical transmittance from 500 to 1000 nm due to ageing treatments was minimal (below 3% for all samples), and unlikely to be due to phase transformation of surface crystals to monoclinic. These results indicate the nc-YSZ has excellent ageing resistance and can withstand long-term implantation conditions without exhibiting LTD.

Enhanced near infrared optical access to the brain with a transparent cranial implant and scalp optical clearing.

We report on the enhanced optical transmittance in the NIR wavelength range (900 to 2400 nm) offered by a transparent Yttria-stabilized zirconia (YSZ) implant coupled with optical clearing agents (OCAs). The enhancement in optical access to the brain is evaluated upon comparing ex-vivo transmittance measurements of mice native skull and the YSZ cranial implant with scalp and OCAs. An increase in transmittance of up to 50% and attenuation lengths of up to 2.4 mm (i.e., a five-fold increase in light penetration) are obtained with the YSZ implant and the OCAs. The use of this ceramic implant and the biocompatible optical clearing agents offer attractive features for NIR optical techniques for brain theranostics.

Optical Access to Arteriovenous Cerebral Microcirculation Through a Transparent Cranial Implant.

BACKGROUND AND OBJECTIVE: Microcirculation plays a critical role in physiologic processes and several disease states. Laser speckle imaging (LSI) is a full-field, real-time imaging technique capable of mapping microvessel networks and providing relative flow velocity within the vessels. In this study, we demonstrate that LSI combine with multispectral reflectance imaging (MSRI), which allows for distinction between veins and arteries in the vascular flow maps produced by LSI. We apply this combined technique to mouse cerebral vascular network in vivo, comparing imaging through the skull, to the dura mater and brain directly through a craniectomy, and through a transparent cranial "Window to the Brain" (WttB) implant. STUDY DESIGN/MATERIALS AND METHODS: The WttB implant used in this study is made of a nanocrystalline Yttria-Stabilized-Zirconia ceramic. MSRI was conducted using white-light illumination and filtering the reflected light for 560, 570, 580, 590, 600, and 610 nm. LSI was conducted using an 810 nm continuous wave near-infrared laser with incident power of 100 mW, and the reflected speckle pattern was captured by a complementary metal-oxide-semiconductor (CMOS) camera. RESULTS: Seven vessel branches were analyzed and comparison was made between imaging through the skull, craniectomy, and WttB implant. Through the skull, MSRI did not detect any vessels, and LSI could not image microvessels. Imaging through the WttB implant, MSRI was able to identify veins versus arteries, and LSI was able to image microvessels with only slightly higher signal-to-noise ratio and lower sharpness than imaging the brain through a craniectomy. CONCLUSIONS: This study demonstrates the ability to perform MSRI-LSI across a transparent cranial implant, to allow for cerebral vascular networks to be mapped, including microvessels. These images contain additional information such as vein-artery separation and relative blood flow velocities, information which is of value scientifically and medically. The WttB implant provides substantial improvements over imaging through the murine cranial bone, where microvessels are not visible and MSRI cannot be performed. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Application of optical flow algorithms to laser speckle imaging.

Since of its introduction in 1980s, laser speckle imaging has become a powerful tool in flow imaging. Its high performance and low cost made it one of the preferable imaging methods. Initially, speckle contrast measurements were the main algorithm for analyzing laser speckle images in biological flows. Speckle contrast measurements, also referred as Laser Speckle Contrast Imaging (LSCI), use statistical properties of speckle patterns to create mapped image of the blood vessels. In this communication, a new method named Laser Speckle Optical Flow Imaging (LSOFI) is introduced. This method uses the optical flow algorithms to calculate the apparent motion of laser speckle patterns. The differences in the apparent motion of speckle patterns are used to identify the blood vessels from surrounding tissue. LSOFI has better spatial and temporal resolution compared to LSCI. This higher spatial resolution enables LSOFI to be used for autonomous blood vessels detection. Furthermore, Graphics Processing Unit (GPU) based LSOFI can be used for quasi real time imaging.

Meso-Scale Particle Image Velocimetry Studies of Neurovascular Flows In Vitro.

Particle image velocimetry (PIV) is used in a wide variety of fields, due to the opportunity it provides for precisely visualizing and quantifying flows across a large spatiotemporal range. However, its implementation typically requires the use of expensive and specialized instrumentation, which limits its broader utility. Moreover, within the field of bioengineering, in vitro flow visualization studies are also often further limited by the high cost of commercially sourced tissue phantoms that recapitulate desired anatomical structures, particularly for those that span the mesoscale regime (i.e., submillimeter to millimeter length scales). Herein, we present a simplified experimental protocol developed to address these limitations, the key elements of which include 1) a relatively low-cost method for fabricating mesoscale tissue phantoms using 3-D printing and silicone casting, and 2) an open-source image analysis and processing framework that reduces the demand upon the instrumentation for measuring mesoscale flows (i.e., velocities up to tens of millimeters/second). Collectively, this lowers the barrier to entry for nonexperts, by leveraging resources already at the disposal of many bioengineering researchers. We demonstratethe applicability of this protocol within the context of neurovascular flow characterization; however, it is expected to be relevant to a broader range of mesoscale applications in bioengineering and beyond.

Evaluation of a transparent cranial implant as a permanent window for cerebral blood flow imaging.

Laser speckle imaging (LSI) of mouse cerebral blood flow was compared through a transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) cranial implant over time (at days 0, 14, and 28, n = 3 mice), and vs. LSI through native skull (at day 60, n = 1 mouse). The average sharpness of imaged vessels was found to remain stable, with relative change in sharpness under 7.69% ± 1.2% over 28 days. Through-implant images of vessels at day 60 appeared sharper and smaller on average, with microvessels clearly visible, compared to through-skull images where vessels appeared blurred and distorted. These results suggest that long-term imaging through this implant is feasible.