Surface characterizations of membranes and electrospun chitosan derivatives by optical speckle analysis

In this paper, we show that laser speckle pattern provides useful information toward revealing discrimination between nanofibers and membranes. Chitosan materials particularly organosoluble chitosan derivatives have a number of applications. The surface characteristics of these materials are very critical for specific applications. The analysis of laser speckles, both numerical and graphical, includes information about the surface structure. The development of digital electronics brought the ease of image processing and has opened new perspectives for a spectrum of laser speckle analysis (LASCA) applications. Our results show reasonable differences between the LASCA parameters of nanofibers and membranes. The methodology may be considered as a quantitative assessment tool for similar samples

Dual-display laparoscopic laser speckle contrast imaging for real-time surgical assistance

Laser speckle contrast imaging (LSCI) utilizes the speckle pattern of a laser to determine the blood flow in tissues. The current approaches for its use in a clinical setting require a camera system with a laser source on a separate optical axis making it unsuitable for minimally invasive surgery (MIS). With blood flow visualization, bowel viability, for example, can be determined. Thus, LSCI can be a valuable tool in gastrointestinal surgery. In this work, we develop the first-of-its-kind dual-display laparoscopic vision system integrating LSCI with a commercially available 10mm rigid laparoscope where the laser has the same optical axis as the laparoscope. Designed for MIS, our system permits standard color RGB, label-free vasculature imaging, and fused display modes. A graphics processing unit accelerated algorithm enables the real-time display of three different modes at the surgical site. We demonstrate the capability of our system for imaging relative flow rates in a microfluidic phantom with channels as small as 200 μm at a working distance of 1–5 cm from the laparoscope tip to the phantom surface. Using our system, we reveal early changes in bowel perfusion, which are invisible to standard color vision using a rat bowel occlusion model. Furthermore, we apply our system for the first time for imaging intestinal vasculature during MIS in a swine

Optogenetically induced functional hyperemia as a model of neurovascular coupling in vivo

Neurovaskuläre Kopplung beschreibt die enge Verbindung zwischen neuraler Aktivität und zerebralem Blutfluss. Unter physiologischen Bedingungen gewährleistet diese Verbindung eine der Aktivität des jeweiligen Gewebes angepasste Blutversorgung. In zahlreichen neurovaskulären und neurodegenerativen Erkrankungen konnte eine abnorme neurovaskuläre Kopplung nachgewiesen werden, die einen potentiellen Zielmechanismus für eine therapeutische Intervention darstellt. Valide experimentelle in vivo Modelle zur Untersuchung der neurovaskulären Kopplung sind somit essentiell. Herkömmliche Modelle haben Nachteile wie die Notwendigkeit einer Kraniotomie oder die Anwendung einer peripheren Stimulation zur Aktivierung des Kortex über subkortikale Bahnen. Dies ist ein Störfaktor, falls die zu untersuchende Pathologie auch subkortikale Zentren beeinflusst. In dieser Studie verwendeten wir optogenetische Stimulation zur direkten Aktivierung des Barrel-Kortex in Thy1-Channelrhodopsin-2-YFP-transgenen Mäusen und quantifizierten die lokalen und räumlich entfernten Veränderungen des kortikalen Blutflusses mittels Laser Speckle Flowmetry. Wir fanden eine von Intensität und Frequenz des Lichtstimulus abhängige Hyperämie im stimulierten Barrel Kortex und im ipsilateralen Motorkortex. Der kontralaterale Barrel-Kortex zeigte eine oligäme Antwort, die elektrophysiologisch mit interhemisphärischer Inhibition korrelierte. Kortikale Streudepolarisierungen, welche bekannterweise die physiologische neurovaskuläre Kopplung unterbrechen, führten in unserem Modell zu einer anhaltenden Halbierung der optogenetisch induzierten Hyperämie. Zusammenfassend zeigen unsere Daten deutliche Überschneidungen der optogenetisch induzierten funktionellen Hyperämie mit der physiologischen neurovaskulären Kopplung und reflektieren bekannte kortikale Konnektivität. Diese Ergebnisse begründen den Einsatz unseres in vivo Modells zur minimal-invasiven Untersuchung von neurovaskulärer Kopplung in neurovaskulären und neurodegenerativen Erkrankungen.Neurovascular coupling describes the close connection between neural activity and cerebral blood flow. Under physiological conditions, this connection ensures a match of supply and demand between blood flow and tissue. Abnormal neurovascular coupling has been demonstrated in several neurovascular and neurodegenerative diseases, representing a potential target mechanism for therapeutic intervention. Therefore, valid experimental in vivo models to study neurovascular coupling are essential. Conventional models have limitations, such as the need for craniotomy or the use of peripheral stimulation to activate the cortex via subcortical pathways. This is a confounding factor if the pathology studied in the model also affects subcortical centers. In this study, we used optogenetic stimulation to directly activate the barrel cortex in Thy1-channelrhodopsin-2-YFP transgenic mice and imaged local and distant changes in cortical blood flow using laser speckle flowmetry. We found hyperemia in the stimulated barrel cortex and the ipsilateral motor cortex, dependent on intensity and frequency of the light stimulus. The contralateral barrel cortex showed an oligemic response that correlated electrophysiologically with interhemispheric inhibition. Cortical spreading depression, which is known to disrupt physiological neurovascular coupling, resulted in a sustained decrease of optogenetically induced hyperemia in our model. In summary, our data show a clear overlap of optogenetically induced functional hyperemia with physiological neurovascular coupling and reflect known cortical connectivity. These results establish the use of our in vivo model for minimally invasive investigation of neurovascular coupling in models of neurovascular and neurodegenerative diseases

Flow detection using optical intereference methods

Práca sa zaoberá optickou metódou LSCI využívajúcou kontrast laserových speklí pre odhad zmien prietoku krvi. Jedná o neinvazíny a technicky pomerne nenáročný prístup, ktorého možnosti pre medicínu zatiaľ neboli plne využité. Literárna rešerš obsahuje podrobný popis tejto metódy zahŕňajúci princíp fungovania, techniky zobrazovania, potenciál pre medicínske aplikácie a tiež limitujúce faktory. Cieľom práce je navrhnúť a zostrojiť kompletný LSCI systém, vrátane vhodných fantómov pre simuláciu tkanivového prietoku krvi. Implementácia zobrazovacích algoritmov pre spracovanie získaných dát bola uskutočnená v prostredí Matlab®. Systém bol podrobený rozsiahlemu testovaniu rôznych parametrov akvizície i spracovania. Výsledky v podobe kvalitívnych prietokových obrazov boli diskutované a konfrontované s teoretickými predpokladmi.The thesis deals with LSCI (Laser Speckle Contrast Imaging), an optical method utilizing laser speckle contrast for the estimation of blood flow changes. LSCI is non-invasive and technically not demanding approach, capabilities of which have not yet been fully exploited. The literature review part contains detailed description of the operating principle, imaging techniques, potential for medical applications with considering the limiting factors. The main aim of the thesis is to design and construct a complete LSCI system including appropriate phantoms able to simulate blood flow through the tissue. Imaging algorithms for the obtained data evaluation were implemented in Matlab® development enviroment. Finally, the created system was tested using different acquisition parameters as well as varying the image processing schemes. The resulting qualitative flow images were subsequently discussed and confronted with the theoretical assumptions.

Laser speckle contrast imaging for intraoperative monitoring of cerebral blood flow

Ensuring adequate blood flow during surgical procedures is crucial, as prolonged ischemia can result in tissue death and lead to poor clinical outcomes. This is especially important during neurosurgery, since the brain relies on a constant supply of cerebral blood flow (CBF) to maintain normal function. Intraoperative blood flow monitoring tools are essential to detect ischemia in a timely manner, and allow surgical correction before the onset of irreversible brain injury. Laser speckle contrast imaging (LSCI) is an optical imaging method that provides blood flow maps with high spatiotemporal resolution, and overcomes many of the limitations of current intraoperative monitoring technologies. The objective of this dissertation is to demonstrate that LSCI is an effective tool for blood flow monitoring during neurosurgery, and to optimize and improve LSCI technology for clinical use. This research has two primary elements: assessing the LSCI instrumentation components in a controlled laboratory setting, and evaluating the clinical performance of LSCI during neurosurgery. The laboratory study aims to determine the optimal specifications for the clinical instrument design, using controlled static and microfluidic flow experiments. Two of the main components of the LSCI instrument are the camera used for recording, and the laser used for coherent illumination of the tissue. Thus, a broad camera and laser comparison was performed spanning a wide array of available hardware options to determine which specifications are the most important for reliable and highly sensitive flow measurements. The two-phase clinical study aims to demonstrate the performance and utility of LSCI in a neurosurgical setting as a potential tool for real-time, continuous, and noninvasive image guidance. These studies demonstrate that LSCI can produce blood flow maps consistent with expected physiological trends, and show the impact of instrument design and image acquisition techniques on image quality and quantitative flow assessment. The results from both the laboratory and clinical studies can be used to design a more sensitive and robust LSCI system, which increases its value as an intraoperative tool for monitoring blood flow. LSCI has the potential to be the next generation of neurosurgical image guidance for blood flow visualization, and the work presented in this dissertation can accelerate its clinical adoption.Biomedical Engineerin

Pulsed Transcranial Ultrasound Stimulation and Its Applications in Treatment of Focal Cerebral Ischemia and Depression

The aims of this thesis were to investigate the therapeutic effects of pulsed transcranial ultrasound stimulation (pTUS) on focal cerebral ischemia and depression, respectively, in rodent models. Neurological and psychiatric disorders, such as Parkinson's disease, epilepsy, Alzheimer's disease, stroke (vascular disorder that results in neurological defects), depression, and etc., present an increasing challenge and a substantial social and economic burden for an aging and stressed population. However, conventional treatments, especially pharmacologic interventions, have significant limitations, such as nonspecific effects, insufficient tailoring to the individual, adverse effects such as drowsiness, weight gain and nausea, or inadequate uptake into the brain due to the blood-brain-barrier (BBB). In contrast, neuromodulation techniques have gained more attention, which are able to enhance or inhibit the neural activities in specific cortex, such as motor, somatosensory or other areas related to cognition. Neuromodulation thus could potentially restore the disrupted neural network due to neurological disorders. Capitalizing on its noninvasiveness, high precision (in the scale of mm) and penetration depth (several centimeters), low-intensity (typically <1 W/cm2 spatial-peak-pulse-average intensity-ISPTA) low-frequency (typically <1MHz), pulsed transcranial ultrasound stimulation (pTUS) has been emerging as a promising therapeutic tool for neurological and psychiatric disorders. This thesis provided the first in-vivo demonstrations that pTUS might serve as neuroprotective preconditioning of ischemic brain injury and treatment of depression. Additionally, it also proposed a novel optical imaging-based technique to characterize the neuromodulatory effect of pTUS, which facilitates the parameter optimization of therapeutic pTUS in practice. Both suppressive and excitatory pTUS are applied in this thesis. The corresponding pTUS parameters were: (a) suppressive pTUS (or pTUSS): ISPPA = 8W/cm2, frequency (f) = 0.5 MHz, pulse repetition frequency (PRF) = 100 Hz, and duty cycle (DC) =5%, and (b) excitatory pTUS (or pTUSE): ISPPA = 8W/cm2, f = 0.5MHz, PRF = 1.5 kHz, and DC = 60%, respectively. Before the therapeutic experiments, the neuromodulatory effects of both pTUSS and pTUSE were examined using laser speckle imaging(LSCI) and multispectral reflectance imaging (MSRI) in aspect of the neurovascular responses. Specifically, this thesis consists of: (1) Study on the neurovascular response to pTUS. Compared with other methods, such as pTUS-triggered motor response and visual evoked potentials (VEP), optical imaging allows to measure the neurovascular change at high spatiotemporal resolution (in the scale of μm and ms), including cortical suppression without evoked output. LSCI and MSRI were used to monitor the primary somatosensory response (Chapter 2) to hind limb electrical stimulation before, immediately, and 1 h after 5-min application of pTUSS and pTUSE, respectively. Several indicators, including Response Index, Peak Response, Latency and Response Duration, were derived from optical images to characterize the neuromodulatory effects of pTUS on primary somatosensory cortex. Our results showed that pTUSS could suppress the primary somatosensory cortex across all rats whereas pTUSE only presented excitatory effects in 5 out of 11 rats. The neuromodulatory effects of pTUS were correlated with the baseline cortical excitability. The results showed that: (i) pTUSs could serve in investigating cognitive function by silencing the neurons in the target region; (ii) pTUSE exposure should be treated with caution due to individual differences in neuromodulatory effects, which were associated with the initial brain state of rats; and (iii) optical imaging was useful in evaluating the pTUS neuromodulatory effects. (2) Neuroprotection of preconditioning pTUS. By applying suppressive pTUS, it was investigated whether the severity of stroke could be minimized or alleviated by prior exposure to ultrasound stimulation (Chapter 3). Preconditioning was supposed to increase the tolerance of brain to subsequent ischemic insult. It can potentially be used to prevent the perioperative stroke in patients undergoing cardiovascular surgeries with a series of complications. Considering the noninvasiveness and safety of ultrasound, pTUS may provide a novel preconditioning method. To test the effectiveness of preconditioning pTUS, rats were randomly assigned to control (n=12) and preconditioning pTUS (pTUS-PC) groups (n=14). The pTUS-PC animals received ultrasound stimulation before the induction of photothrombotic stroke, whereas control animals were handled identically except the ultrasound stimulation. The cerebral blood flow was monitored using LSCI in both groups during stroke induction, as well as 24 hours and 48 hours after stroke, respectively. Also, infarct volumes and edema were measured at 48 hours after euthanatizing the rats. Results showed that pTUS-PC rats had smaller ischemic volume during stroke induction, as well as 24 hours and 48 hours after the stroke than the controls. Moreover, the pTUS-PC group showed lower volume of brain edema than the control group. (3) Antidepressant-like effect by pTUS. The potential antidepressant-like effects of pTUS were further investigated in a rat model of depression with excitatory pTUS. Stimulating the left prefrontal cortex (PFC) by TMS has been clinically used for depression treatment, it was thus hypothesize that pTUSE on PFC would act similarly with TMS and result in antidepressant-like effect. To test this hypothesis, pTUS was applied for 2 weeks daily to the left PFC of depressed rats induced by 48-hour restraint. The long-term (3 weeks) efficacy of the depression model as well as the antidepressant-like effects of pTUS were investigated with a group of behavioral tests. In addition, the hippocampal BDNF was measured by western blot to study the mechanisms underlying antidepressant-like effects of pTUS. The safety of long-term (2 weeks) pTUS was assessed by histologic analysis. Results showed that 48-hour-restraint stress could stably lead to at least 3-week reduction of exploratory behavior and protracted anhedonia, whereas pTUSE treatment could successfully reverse the depression-like phenotypes and promote the BDNF expression in the left hippocampus. In addition, H& E staining of brain tissues confirmed the safety of the long-term pTUS treatment. In conclusion, the results in this work suggested that pTUS could serve as preconditioning of perioperative stroke and therapeutics for depression. Additionally, the results also demonstrated that optical neurovascular imaging could measure the neuromodulatory effect of pTUS. This study documented more evidence that pTUS is a promising tool for basic neuroscience and therapeutic applications. KEY WORDS: Neurological and psychiatric disorders, brain stimulation, pulsed ultrasound stimulation, neurovascular imaging, preconditioning, stroke, depression.Ph.D., Biomedical Engineering -- Drexel University, 201

Development of zebrafish and computational models of neurovascular coupling in health and disease

In this thesis, I have developed a novel zebrafish model of neurovascular coupling. Combining lightsheet imaging, compound transgenic zebrafish models and custom MATLAB based analysis pipelines, I characterised the neurovascular responses (neuronal calcium increases and change in red blood cell speed) in the optic tectum in response to visual stimulation. I determined the development stage at which neurovascular coupling in zebrafish larvae develops, followed by testing the requirement for nitric oxide or astrocyte cyclo-oxygenase in my model. I then used this model to investigate factors influencing neurovascular function. I first characterized the effect of glucose exposure and the role of nitric oxide in modulating neurovascular coupling. I then examined the effect of genetic mutation of Guanosine Triphosphate cyclohydrolase (an enzyme involved in nitric oxide and dopamine production in the brain) on neurovascular coupling. Finally, I have developed a minimal mathematical model of the neurovascular unit. To demonstrate the potential of this model I have simulated the effect of high blood glucose and low nitric oxide on neurovascular coupling and show this conforms with experimental data obtained in zebrafish