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Background and Objectives:Although abnormal blood flow is linked to clinical risk of illness in neonates, clinicians typically do not integrate flow measurements into routine monitoring in the neonatal intensive care unit (NICU). We and other research groups have previously demonstrated the ability of Laser Speckle Imaging (LSI) to measure changes in blood flow in both a laboratory and clinical settings. We postulate that LSI, in a clinic-friendly form factor, can provide important hemodynamic information in the NICU. Here, I describe initial efforts to develop a handheld LSI system and deploy it to University of California, Irvine Medical Center NICU.Study Design/Methods:I designed and fabricated a handheld LSI system based on design principles to insure successful implementation into a clinical setting. Using in-vitro tissue phantom systems, I assessed the system performance of handheld LSI versus a traditional mounted configuration. I collected multi-user data (n=7) to assess the variation in flow measurements attributed to user performance. I collected data from two in-vivo occlusion models to demonstrate that the handheld device can detect both qualitative and quantitative changes in blood flow. Finally, I acquired data from an on-going NICU based clinical study (n=30, to date) in which we collected LSI images of abdomen and the heel over a period of several months.Results:I demonstrate that the handheld nature of the device has little effect on the flow measurement sensitivity via a study that was focused on the characterization of tissue simulating phantoms. Flow phantoms were characterized using both bench top and handheld LSI instruments. I show that measurements of flow from these phantoms is not user dependent based on testing using a pool of 7 minimally trained users. I demonstrate that the handheld LSI system measures trends in flow that are similar to those reported previously using bench top LSI systems during in-vivo occlusion models. I observed up to an 83.9% increase in flow index measured in neonates at the abdomen after feeding, while only up to a 16.1% increase was observed in the heel. Lastly, I observed a statistically significant difference between the maximum range of flow index values measured at the abdomen in necrotizing enterocolitis neonates and a healthy population (P=.015).Conclusion:The handheld LSI system can measure changes in blood flow and is minimally sensitive to errors due to handheld motion. Flow changes found in the abdomen warrant further studies to investigate the feasibility of using the LSI to detect compromised intestinal blood flow in neonates. These results suggest that LSI may be capable of providing additional screening for neonates with suspected gut pathology.

Roughly 400,000 children each year are born with port wine stain (PWS) birthmarks, which are skin capillary malformations characterized by a pink-reddish color that develop into purple nodules if left untreated. While PWS birthmarks can be found anywhere on the body and are typically non-life threatening, a large majority (~90%) present on the head and neck regions and can lead to complications including dental abnormalities and may be associated with capillary malformations in other organs such as the eyes (glaucoma), and brain (seizures). Due to the unsightly nature of PWS, people that have them on exposed areas of skin (face, neck, arm or leg regions) can endure immense psychological and social suffering. The current gold standard treatment for PWS in the US is laser irradiation using the pulsed dye laser (PDL). Treatment of PWS with the PDL has limited efficacy; many patients undergo 15 or more laser treatments without seeing full clearance of the PWS, demonstrating the need to investigate alternative therapies. In my dissertation research, I investigated alternatives to PDL treatment for PWS, including photodynamic therapy (PDT), combined PDT/PDL protocols, and alternative light based treatments. PDT has demonstrated promise towards achieving better treatment outcomes for PWS birthmarks, however, careful selection of treatment parameters is needed to avoid unwanted side effects. I performed preclinical studies of PDT using two photosensitizers, NPe6 and Hemoporfin, to better develop safe treatment parameters. I then investigated a combined PDT/PDL protocol and determined that a synergistic effect exists between the PDT and PDL protocols, illustrating that this combined approach leads to a desired treatment outcome while minimizing side effects. To better understand the PDT treatment mechanisms in skin, I also studied the depth of injury caused by NPe6-mediated PDT in preclinical models and found a direct relationship between depth of vascular injury and light dose administered. Finally, in investigating alternatives to the PDL, I studied the use of intense pulsed light (IPL) and performed a direct comparison study to the PDL. I used computational models to characterize the predicted performance of the IPL and performed experimental studies in preclinical models.

Induced hypothermia has been broadly applied in neurological intensive care unit (NICU). Meanwhile, accidental hypothermia is also a threatening condition in daily life. It is meaningful to investigate the influences of temperature change on the cerebral blood flow (CBF). In the present study, temporal laser speckle image contrast analysis (tLASCA) was implemented to study the relative CBF change in cerebral artery, vein and capillary level under mild (35 degrees C) and moderate (32 degrees C) hypothermia. Twelve male Sprague-Dawley rats (300 +/-50 g) were anesthetized with sodium pentobarbital and randomly assigned to mild and moderate hypothermia groups (n=9 each). Laser speckle imaging (LSI) trials were acquired from baseline (37 degrees C), hypothermia (35 degrees C or 32 degrees C), and post-rewarming (37 degrees C) phases. In the mild group, mean CBF in different vessels all increased throughout the hypothermic and post-rewarming phases. On the contrary, mean CBF reduced by 10%-20% at 32 degrees C and returned to approximately 95% of the baseline level during the post-rewarming session in the moderate group. Besides, in the moderate group, a CBF rebound in vein was found in the post-rewarming phase. Our results suggested that the CBF changed differently between mild and moderate hypothermia, which may be worth for further study in clinic. And we demonstrated LSI as a promising method to achieve high spatiotemporal resolution CBF change with minimal invasion.

We present experimental demonstration of laser speckle intensity based methods to follow the drying process of white adhesive. Results obtained using graphical methods such as temporal LASCA, GD, Fujii and parameterized Fujii as well as numerical methods of Inertia moment and temporal correlation show that qualitative and quantitative evaluation of spatial temporal speckle activities can be used to monitor drying process of adhesives. Statistical Tukey’s test for the mean values of inertia moments at 5% significance level allowed differentiating different stages of drying.

The light source-based medical techniques for brain imaging, diagnosis, and treatment are very common clinical tools. However, applying these techniques is limited due to the high attenuation of light in the scalp and skull. Such optical attenuation reduces the achievable spatial resolution and precludes the visualization of small features such as brain microvessels. The present study aims to clarify the current methods for providing a desired optical access to the brain with good visualization of the microvessels. The strategy involves the use of transparent cranial implants and optical clearing agents to improve the optical access for laser speckle imaging of cerebral microvasculature. In vivo laser speckle imaging experiments of the mouse, cerebral blood vessels showed that the proposed optical access with combined transmittance of the optically cleared scalp overlying the transparent cranial implant increased signal to noise ratio and image resolution, allowing for visualization of microvessels through the transparent implant, which was not possible through the uncleared scalp and intact skull.

Laser Speckle Imaging (LSI) method is the imaging of light interference events when it interacts on a rough surface. A laser beam which entered the surface of skin will experience reflection, refraction and scattering. Interaction between a laser beam with the surface of the skin when entering to membranes blood, provides contrast information that were resulted from the rays scattered in a certain position, recorded by a CMOS camera and translated by imageJ program. A picture will provide an information of the intensity from certain skin areas with dark light pattern which keeps blind due to the presence of blood flow that does not dwell. The result of contrast imaging was validated with direct measurement by blood glucose device. The objects were people with the age range of 17 until 63 years old. This study aims to find the correlation between contrast Speckle to blood sugar levels in the human body. The result revealed that correlation between contrast intensity of red, green and blue to glucose level are 0.3275; 0.3165; 0.3050 respectively, and then correlation between contrast intensity to age are 0.6410; 0.6554; 0.6526. The data indicated high correlation on contrast to age and average correlation on contrast to glucose blood level.

Effective defects detection method for silicone polymer insulators is desperately needed to eliminate defective insulators in factory examination and make early warnings for accidents of in-service insulators. This paper investigates a laser shearography method that reveals surface deformation anomalies induced by internal defects after applying thermal excitation. Samples with artificial defects of different sizes and depths in the silicone rubber sheath were tested. Both fringe patterns and phase distribution maps were generated after the experiments for defects identification by indicating the displacement derivative with respect to the shearing direction. The relationship between the defect parameters and the relative phase difference was discussed, and a parameter named detection sensitivity was defined to evaluate the system detection ability on different defects. Finally, Canny edge detection algorithm and proposed image gradient method were employed to quantitatively estimate the defect size, and the ability of identifying defects was also improved. With its noncontact testing, full-field measurement, real-time imaging, and visual results, laser speckle imaging would have quite promising applications in nondestructive testing of silicone polymer insulators and it can be extended for other composite materials insulating equipment.

Background Functional magnetic resonance imaging (fMRI) in awake behaving mice is well positioned to bridge the detailed cellular-level view of brain activity, which has become available owing to recent advances in microscopic optical imaging and genetics, to the macroscopic scale of human noninvasive observables. However, though microscopic (e.g., two-photon imaging) studies in behaving mice have become a reality in many laboratories, awake mouse fMRI remains a challenge. Owing to variability in behavior among animals, performing all types of measurements within the same subject is highly desirable and can lead to higher scientific rigor. Methods We demonstrated blood oxygenation level–dependent fMRI in awake mice implanted with long-term cranial windows that allowed optical access for microscopic imaging modalities and optogenetic stimulation. We started with two-photon imaging of single-vessel diameter changes (n = 1). Next, we implemented intrinsic optical imaging of blood oxygenation and flow combined with laser speckle imaging of blood flow obtaining a mesoscopic picture of the hemodynamic response (n = 16). Then we obtained corresponding blood oxygenation level–dependent fMRI data (n = 5). All measurements could be performed in the same mice in response to identical sensory and optogenetic stimuli. Results The cranial window did not deteriorate the quality of fMRI and allowed alternation between imaging modalities in each subject. Conclusions This report provides a proof of feasibility for multiscale imaging approaches in awake mice. In the future, this protocol could be extended to include complex cognitive behaviors translatable to humans, such as sensory discrimination or attention.

In this paper we present a method of zero-padding temporal auto-correlation imaging (ztDCI) for imaging blood flows. Compared with temporal auto-correlation imaging (tDCI), ztDCI effectively slows down the decorrelation speed of speckle frames, so it has wider applicable speed range. We also prove that the combination of tDCI and ztDCI can compensate the non-monotonous trend of ztDCI VS speed and provides higher relative signal to noise rate (rSNR) for slow flows and short exposure times than laser speckle contrast imaging (LSCI). It captures both slow and fast flows independent of camera exposure time which will be an advantage for in vivo or clinical applications.

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.

While clinical examination is needed for burn severity diagnosis, several emerging technologies aim to quantify this process for added objectivity. Accurate assessments become easier after burn progression, but earlier assessments of partial thickness burn depth could lead to earlier excision and grafting and subsequent improved healing times, reduced rates of scarring/infection, and shorter hospital stays. Spatial Frequency Domain Imaging (SFDI), Laser Speckle Imaging (LSI) and thermal imaging are three non-invasive imaging modalities that have some diagnostic ability for noninvasive assessment of burn severity, but have not been compared in a controlled experiment. Here we tested the ability of these imaging techniques to assess the severity of histologically confirmed graded burns in a swine model. Controlled, graded burn wounds, 3 cm in diameter were created on the dorsum of Yorkshire pigs (n=3, 45–55kg) using a custom-made burn tool that ensures consistent pressure has been employed by various burn research groups. For each pig, a total of 16 burn wounds were created on the dorsal side. Biopsies were taken for histological analysis to verify the severity of the burn. Clinical analysis, SFDI, LSI and thermal imaging were performed at 24 and 72 hours after burn to assess the accuracy of each imaging technique. In terms of diagnostic accuracy, using histology as a reference, SFDI (85%) and clinical analysis (83%) performed significantly better that LSI (75%) and thermography (73%) 24 hours after the burn. There was no statistically significant improvement from 24 to 72 hours across the different imaging modalities. These data indicate that these imaging modalities, and specifically SFDI, can be added to the burn clinicians’ toolbox to aid in early assessment of burn severity.

Adequate tissue perfusion is essential to minimize postoperative complications following microsurgery. Intraoperative knowledge of tissue perfusion could aid surgical decision-making and result in reduced complications. Laser speckle imaging is a new, noninvasive technique for mapping tissue perfusion. This article discusses the feasibility of using laser speckle imaging during free flap breast reconstruction and its potential to identify areas of inadequate perfusion, thus reducing surgical complications. Adult patients scheduled to undergo free flap breast reconstruction were recruited into the study. Laser speckle images were obtained from the abdominal and breast areas at different stages intraoperatively. Zonal perfusion was compared with the Holm classification and clinical observations. Twenty patients scheduled to undergo free flap breast reconstruction were recruited (23 reconstructed breasts) (mean age, 50 years; range, 32 to 68 years). Flap zonal perfusion was 238 (187 to 313), 222 (120 to 265), 206 (120 to 265), and 125 (102 to 220) perfusion units for zones I, II, III, and IV, respectively (analysis of variance, p < 0.0001). Zonal area with perfusion below an arbitrary perfusion threshold were 20 (0.3 to 75), 41 (3 to 99), 49 (9 to 97), and 99 (25 to 100) percent, respectively (analysis of variance, p < 0.0001). One example is presented to illustrate potential intraoperative uses for laser speckle imaging. This study shows that laser speckle imaging is a feasible, noninvasive technique for intraoperative mapping of tissue perfusion during free flap breast reconstruction. Zonal tissue perfusion was reduced across the Holm classification. Observations indicated the potential for laser speckle imaging to provide additional information to augment surgical decision-making by detection of inadequate tissue perfusion. This highlights the opportunity for surgeons to consider additional aids for intraoperative tissue perfusion assessment to help reduce perfusion-related complications. CLINICAL QUESTION/LEVEL OF EVIDENCE:: Diagnostic, IV.

Chemical fixation is the slowest and often the most uncontrolled step in the multi-step process of preparing tissue for histopathology. In order to reduce the time from taking a core needle biopsy to making a diagnosis, a new approach is proposed that optically monitors the common formalin fixation process. A low-cost and highly-sensitive laser speckle imaging technique is developed to measure shear wave velocity in a biospecimen as small as 0.5 mm in thickness submerged in millifluidic channels. Shear wave velocity, which is the indicator of tissue mechanical property and induced by piezoelectric-actuation, was monitored using gelatin phantom and chicken breast during fixation, as well as post-fixed liver and colon tissues from human. Fixation levels in terms of shear wave velocity increased by approximately 271.0% and 130.8% in gelatin phantom and chicken breast, respectively, before reaching the plateaus at 10.91 m/s and 7.88 m/s. Within these small specimens, the plateaus levels and times varied with location of measurement, and between gelatin and chicken breast. This optical-based approach demonstrates the feasibility of fine-tuning preanalytical variables, such as fixation time, for a rapid and accurate histopathological evaluation; provides a quality metric during the tissue preparation protocol performed in most pathology labs; and introduces the millifluidic chamber that can be engineered to be a future disposable device that automates biopsy processing and imaging., We propose a new approach to histopathology: optically monitoring the common formalin fixation process. A low-cost and highly-sensitive laser speckle imaging technique is used to measure shear wave velocity in a biospecimen as small as 0.5 mm. This approach demonstrates the feasibility of fine-tuning preanalytical variables, such as fixation time, for rapid and accurate histopathological evaluation; provides a quality metric during tissue preparation; and introduces a millifluidic chamber that holds the potential to be a disposable device that automates biopsy processing and imaging.

We describe the development of a perturbation-free technique to measure tissue blood flow and metabolic rate of oxygen (MRO2) using LSI and SFDI. Analytical (diffusion) and computational (Monte Carlo) models are employed to characterize the contributions of diffuse and directed flow to the measured speckle contrast. Measured flow data is combined with the deoxygenated hemoglobin concentration and a path-length factor (both obtained from SFDI) to model tissue oxygen consumption in units of M O2/min. The results of this model were comparable with values of MRO2 measured with other imaging methods (PET, MRI/MRS).

Spatial Frequency Domain Imaging (SFDI) is a powerful technique for non-contact tissue optical property and chromophore mapping over a large field of view. However, a major challenge that limits the clinical adoption of SFDI is that it requires carefully-controlled imaging geometry and the projection of known spatial frequencies. We present speckle-illumination SFDI (si-SFDI), a projector-free technique that measures tissue optical properties from structured illumination formed by randomized speckle patterns. We compute the local power spectral density of images under speckle illumination, from which a high-frequency and a low-frequency tissueresponse parameter can be characterized for each pixel. A lookup table generated by Monte-Carlo simulations is subsequently used to accurately determine optical absorption and reduced scattering coefficients. Compared to conventional SFDI, si-SFDI may be particularly useful for endoscopic applications due to its utilization of simple coherent illumination, which makes it more easily incorporated into existing endoscopic systems. Moreover, speckle illumination offers a large depth of focus compared to projector-based illumination. In this study, we explore wide-field optical property mapping with an endoscope camera and fiber-coupled laser speckle illumination. We apply this technique to tissue-mimicking silicone phantoms and biological tissues. The accuracy of si-SFDI is evaluated by comparing to optical properties measured by conventional SFDI. Future work could accelerate si-SFDI reconstruction by using parallel computing or machine learning algorithms.

Dynamic laser speckle imaging (DLSI) is an optical technique that directly measures the temporal speckle intensity fluctuations with sufficient temporal sampling to correctly model and predict the underlying blood flow changes. The speckle measurements are limited to superficial tissues and it lacks three-dimensional imaging of blood flow. To perform depth-resolved measurement, we developed Interferometric Dynamic Laser Speckle Imaging (iDLSI) capable of three-dimensional volumetric measurements of the dynamics. Here, we present the analytical expression for g2,iDLSI(τ) dependent on particle dynamics, coherence properties, sample, and reference intensity. The numerical validations are performed in a homogeneous and in spatially varying dynamic regions.

While visual clinical impression is the standard of care for burn severity assessment, accuracy improves after the injury progresses, leading to patients waiting days for a diagnosis. Spatial Frequency Domain Imaging (SFDI) has shown the potential to assess burn grade as early as 24 hours post-burn. Here, we compared SFDI and Laser Speckle Imaging (LSI) at 24 and 72 hours after burn injury to clinical burn severity diagnosis. Three patients with burns ranging in severity were imaged. Both techniques showed an ability to categorize burn severity 24 hours after the initial injury, well before the outcome was determined by a clinician at 72 hours or later.

Non-invasive assessment of tissue perfusion has gained increased interest in the recent past for monitoring various physiological dysfunctions. Laser speckle imaging and associated processing techniques present useful and inexpensive methods of achieving this goal. However, differentiating the effects of static and dynamic scatterers from the captured speckle image is challenging and limits the sensitivity of such techniques. This paper presents a fractal analysis in the temporal domain to assess the various dynamic scattering features of tissue perfusion demonstrated on a perfusion model. We use detrended fluctuation analysis for the quantitative assessment of image fractal dimensions, which reflect the concentration and flow features of the moving scatterers in the perfusion model.

Background The regulation of cerebral blood flow is critical for normal brain functioning, and many physiological and pathological conditions can have long-term impacts on cerebral blood flow. However, minimally invasive tools to study chronic changes in animal models are limited. New method We developed a minimally invasive surgical technique (cyanoacrylate skull, CAS) allowing us to image cerebral blood flow longitudinally through the intact mouse skull using laser speckle imaging. Results With CAS we were able to detect acute changes in cerebral blood flow induced by hypercapnic challenge. We were also able to image cerebral blood flow dynamics with laser speckle imaging for over 100 days. Furthermore, the relative cerebral blood flow remained stable in mice from 30 days to greater than 100 days after the surgery. Comparison with existing methods Previously, achieving continuous long-term optical access to measure cerebral blood flow in individual vessels in a mouse model involved invasive surgery. In contrast, the CAS technique presented here is relatively non-invasive, as it allows stable optical access through an intact mouse skull. Conclusions The CAS technique allows researcher to chronically measure cerebral blood flow dynamics for a significant portion of a mouse’s lifespan. This approach may be useful for studying changes in blood flow due to cerebral pathology or for examining the therapeutic effects of modifying cerebral blood flow in mouse models relevant to human disease.

The aim of this study is to evaluate whether the blood perfusion to tissues for detecting ischemic necrosis can be quantitatively monitored by spatial frequency domain imaging (SFDI) and laser speckle imaging (LSI) in a skin flap mouse model. Skin flaps were made on Institute of Cancer Research (ICR) mice. Using SFDI and LSI, the following parameters were estimated: oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), total hemoglobin (THb), tissue oxygen saturation (StO2), and speckle flow index (SFI). Histologically, epithelium thickness, collagen deposition, and blood vessel count of skin flap tissues were analyzed. Then, the correlation of SFDI and histological results was assessed by application of Spearman rank correlation method. As the result, the number of blood vessels and the percentage of collagen areas showed significant difference between the necrotic tissue group and the non-necrotic one. Especially, the necrotic tissue had a complete epithelial loss and loses its normal structure. We identified that SFDI/LSI parameters were significantly different between non-necrotic and necrotic tissue groups. Especially, all SFDI and LSI parameters measured on the 1st day after surgery showed significant difference between necrotic tissue and non-necrotic tissue. In addition, the number of blood vessel and percentage of collagen area were positively correlated with HbO2 and StO2 among SFDI/LSI parameters. Meanwhile, the number of blood vessel and percentage of collagen area showed the negative correlation with Hb. By applying SFDI and LSI simultaneously to the skin flap, we could quantitatively monitor the blood perfusion and the tissue condition which can help us to detect ischemic necrosis objectively in early stage.

The ability of the laser speckle imaging (LSI) to map image of the blood flow in real-time with high spatio-temporal resolution using simple and powerful tool makes it the robust neurodiagnostic tool. Over the past decade the acceptability of LSI at various stages of clinical use has further increased. Laser speckle contrast imaging (LSCI) is a relatively simple, inexpensive, fast, full-field imaging method that can provide 2D perfusion maps. Although blood flow measurements initiated with the surface tissues without enough depth resolution, LSCI has been instrumental in preclinical studies on various neurological disorders, as well as in clinical applications including dermatological, neurosurgical, retinal, and endoscopic studies. Numerous technical advancements have recently been reported to improve the quantitative accuracy and temporal resolution of spotted images. This chapter provides an overview of LSCI and its applications in modern biology.

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.

Surface roughness evaluation of optically rough metal plate (Al-6061) by laser speckle imaging method is reported. When the crust portion of metal is illuminated by the monochromatic laser beam, the reflected light from the surface produce granular speckle pattern due to the composite effect of scattering and interference. The captured pattern is used for roughness assessment by soft computing technique. The results are fair in consent while compared with the conventional stylus profiler.

This paper demonstrates a novel approach for fast, single-shot Multi-Exposure Speckle Imaging of blood flow with a simplified imaging setup. Our method can transform existing single-exposure speckle images to quantitative flow images.

Understanding phenomena such as evaporation and imbibition of picoliter droplets into porous substrates is crucial in printing industry to achieve a higher printing quality and print speed. After printing, the residual pigment must remain fixed at the desired location on a substrate and be of a desired volume to yield a high resolution and vibrantly printed page that has become the expectation of modern printing technology. Current research entails not only chemical composition of the ink but also how this links to the dynamics and interactions that occur between the ink and the substrate at every stage of the printed spot formation, including evaporation, wetting, and imbibition. In this paper, we present an instrument that can print on-demand picoliter volume droplets of ink onto substrates and then immediately record on evolution of the resulting dynamics when these two materials interact. This high-speed laser speckle imaging (HS-LSI) technique has been developed to monitor nanometer displacement of the drying and imbibing ink droplet at a high frame rate, up to 20000 Hz, given the short timescales of these interactions. We present the design of the instrument, discuss the related challenges and the theory underlying the LSI technique, specifically how photons non-evasively probe opaque objects in a multiple scattering regime, and show how this technique can unravel the dynamics of drying and imbibition. We will finish giving a validation on the instrument and an example of its usage.

Background: Basilar artery occlusion (BAO) is a subset of posterior circulation stroke that carries a mortality as high as 90%. The current clinical standard to diagnose ischemic stroke include computerized tomography (CT), CT angiography and perfusion and magnetic resonance imaging (MRI). Large animal pre-clinical models to accurately reflect the clinical disease as well as methods to assess stroke burden and evaluate treatments are lacking. Methods: We describe a canine model of large vessel occlusion (LVO) stroke in the posterior circulation, and developed a laser speckle imaging (LSI) protocol to monitor perfusion changes in real time. We then utilized high b-value DWI (b=1800s/mm2) MRI to increase detection sensitivity. We also evaluated the ability of magnetic resonance angiography (MRA) to assess arterial occlusion and correlate with DSA. Finally, we verified infarct size from apparent diffusion coefficient (ADC) mapping with histology. Results: Administration of thromboembolism occluded the basilar artery as tracked by DSA (n=7). LSI correlated with DSA, demonstrating a reduction in perfusion after stroke onset that persisted throughout the experiment, allowing us to monitor perfusion in real time. DWI with an optimized b-value for dogs illustrated the stroke volume and allowed us to derive ADC and magnetic resonance angiography (MRA) images. The MRA performed at the end of the experiment correlated with DSA performed after occlusion. Finally, stroke burden on MRI correlated with histology. Conclusions: Our studies demonstrate real time perfusion imaging using LSI of a canine thromboembolic LVO model of posterior circulation stroke, which utilizes multimodal imaging important in the diagnosis and treatment of ischemic stroke.

Artworks have a layered structure subjected to alterations caused by various factors. The monitoring of defects at sub-millimeter scale may be performed by laser interferometric techniques. The aim of this work was to develop a compact system to perform laser speckle imaging in situ for effective mapping of subsurface defects in paintings. The device was designed to be versatile with the possibility of optimizing the performance by easy parameters adjustment. The system exploits a laser speckle pattern generated through an optical diffuser and projected onto the artworks and image correlation techniques for the analysis of the speckle intensity pattern. A protocol for the optimal measurement was suggested, based on calibration curves for tuning the mean speckle size in the acquired intensity pattern. The system was validated in the analysis of detachments in an ancient painting model using a short pulse thermal stimulus to induce a surface deformation field and standard decorrelation algorithms for speckle pattern matching. The device is equipped with a compact thermal camera for preventing any overheating effects during the phase of the stimulus. The developed system represents a valuable nondestructive tool for artwork diagnostics, allowing the monitoring of subsurface defects in paintings in out-of-laboratory environment.

Roughness being a crucial feature of the surface texture is estimated through numerous techniques. The laser speckle imaging method has emerged as an efficient non-contact tool in the regime of surface roughness measurement techniques. This work presents singular value decomposition-based roughness measurement using objective speckle patterns of the machined surfaces. The surface roughness is quantified as a function of a proposed metric which is the exponential decay rate of the singular values associated with the speckle pattern. The effect of surface correlation length on the proposed metric is investigated and compared with speckle contrast and bright to dark pixel ratio of the binarized speckle pattern. The experimental results demonstrate the broad range surface roughness measuring capability of the proposed method using a single laser source.