Browsing by Subject "Ultrasound"

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All-optical ultrasound transducers for high resolution imaging
(2014-12) Sheaff, Clay
High frequency ultrasound (HFUS) has increasingly been used within the past few decades to provide high resolution (< 200 µm) imaging in medical applications such as endoluminal imaging, intravascular imaging, ophthalmology, and dermatology. The optical detection and generation of HFUS using thin films offers numerous advantages over traditional piezoelectric technology. Circumvention of an electronic interface with the device head is one of the most significant given the RF noise, crosstalk, and reduced capacitance that encumbers small-scale electronic transducers. Thin film Fabry-Perot interferometers - also known as etalons - are well suited for HFUS receivers on account of their high sensitivity, wide bandwidth, and ease of fabrication. In addition, thin films can be used to generate HFUS when irradiated with optical pulses - a method referred to as Thermoelastic Ultrasound Generation (TUG). By integrating a polyimide (PI) film for TUG into an etalon receiver, we have created for the first time an all-optical ultrasound transducer that is both thermally stable and capable of forming fully sampled 2-D imaging arrays of arbitrary configuration. Here we report (1) the design and fabrication of PI-etalon transducers; (2) an evaluation of their optical and acoustic performance parameters; (3) the ability to conduct high-resolution imaging with synthetic 2-D arrays of PI-etalon elements; and (4) work towards a fiber optic PI-etalon for in vivo use. Successful development of a fiber optic imager would provide a unique field-of-view thereby exposing an abundance of prospects for minimally-invasive analysis, diagnosis, and treatment of disease.
Brachial Artery Response to Reactive Hyperemia: Describing High-Flow-Mediated Constriction in Healthy Children, Adolescents and Adults, and the Intra- and Inter-day Reproducibility of High-Flow-Mediated Constriction Response in Adults
(2016-07) Ostrem, Joseph
Endothelial dysfunction has been shown to be an important precursor in the atherosclerotic process. A widely used, non-invasive method of assessing endothelial function is flow-mediated dilation (FMD). This method of vascular health assessment utilizes ultrasound imaging and has historically focused on the degree of vessel dilation in response to reactive hyperemia to ascertain endothelial function. The brachial artery's ideal vessel diameter and its nitric oxide-mediated response to reactive hyperemia make it the preferred site of assessment. Also, a strong correlation between endothelial function in coronary and brachial arteries has been reported, which allows brachial FMD to be a surrogate measure of coronary function. Additionally, many studies have shown impairment of FMD in response to a range of cardiovascular risk factors and has been inversely associated with future CVD events. However, a biphasic response, where vessel constriction occurs prior to dilation, has been observed during reactive hyperemia. The constriction phase during reactive hyperemia has been largely overlooked in FMD research, termed high-flow-mediated constriction (H-FMC). Therefore, the purpose of the following dissertation was to perform a cross-sectional examination of children, adolescents and adults to quantify the frequency and magnitude of H-FMC, determine potential influences of sex, age, body composition, cardiovascular and metabolic factors on H-FMC, and report the reproducibility of an H-FMC in young adults to lend further insight to the existing body of research surrounding FMD and H-FMC assessment.
Comparison of baseline brachial artery measurements and effect on peak flow-mediated dilation
(2013-08) Ostrem, Joseph Dwayne
The aim of this study was to examine the effect of pre-occlusion, occlusion, and post-occlusion baseline brachial artery measurements on the calculation of peak flow mediation dilation (FMD). Ultrasound imaging of the brachial artery following reactive hyperemia was conducted in 418 children and 533 adults. Baseline brachial artery measures were a 10-second average before (pre-occlusion), during (occlusion), and after (post-occlusion) hyperemia. Peak FMD was defined as the change from baseline to the peak brachial artery diameter following reactive hyperemia. Pre-occlusion, occlusion, and post-occlusion baseline measures of brachial artery diameter were not significantly different in children (3.15±0.51, 3.14±0.50 vs. 3.11±0.50 mm, P=0.179) or adults (3.81±0.72, 3.81±0.73 vs. 3.79±0.73 mm, P=0.201). Peak FMD values were not significantly different when calculated from pre-occlusion, occlusion, or post-occlusion baselines in children (6.77±5.78, 6.93±4.03 vs. 7.85±3.62%, P=0.208) or adults (6.06±5.53, 6.12±3.94 vs. 6.62±3.70%, P=0.266). We found no differences in FMD regardless of the baseline brachial artery diameter used in children or adults. Therefore, comparison of data from studies utilizing different measures of baseline brachial diameter can be conducted without correction of data.
Computer-aided renal allograft assessment using ultrasound elastography and machine learning
(2022-05) Vasconcelos, Luiz Henrique
Rheological tissue parameters have been shown to correlate with specific histological characteristics related to different pathologies and specifically to kidney rejection. For decades, kidney function tests and biopsy have been used as the main assessment methods for allograft health. With this work we are creating novel approaches for reliable and non-invasive allograft assessment tools by using shear wave elastography measurements with different machine learning algorithms to model the mechanical properties and the pathological changes in the tissue. We also propose to interpret the findings leveraging game theory analysis of the model inputs and outputs to understand what parameters are contributing most for the model prediction. We also intend to better comprehend the progress of kidney rejection from microscopic to macroscopic scales using histology-based models of shear wave propagation. Finally, we propose to create a fast, reliable, and non-invasive allograft assessment method by analyzing the shear wave propagation with minimal signal processing, leveraging convolutional neural networks architectures to retrieve the features from two-dimensional Fourier transform analysis of shear wave data, without the use of complex mathematical and physical models.
Development of a Vagus Nerve Stimulation and Recording Setup for Ultrasound Characterization
(2016-08) Mehta, Pooja
The objective for my MS Thesis was to develop a stable electrical stimulation and recording preparation for the vagus nerve in guinea pigs so that ultrasound stimulation on this pathway can be studied robustly. In particular, the plan was to electrically stimulate the vagus nerve and characterize the response patterns (i.e., different components and peaks of the evoked compound action potential corresponding to different subpopulation of fibers) using electrodes wrapped around the nerve. Ultrasound stimulation of the vagus nerve can then be performed and the corresponding response patterns can be compared with those caused by electrical stimulation to assess how ultrasound is activating the vagus nerve. Ultrasound stimulation will also be performed while electrically stimulating the vagus nerve to assess suppressive or modulatory effects of ultrasound. To further demonstrate proof-of-concept of US neuromodulation in a simplified preparation, I assessed how ultrasound stimulation with electrical stimulation of the vagus nerve modulates the heart rate in guinea pigs. The long term goal is to develop a non-invasive method for modulating vagus nerve activity that can have clinical applications for treating inflammatory disorders, seizures, depression, tinnitus, and other conditions that may be modulated by the vagus nerve.
Endothelium-independent dilation in children and adolescents
(2011-08) Marlatt, Kara Lynn
Peak brachial artery dilation post-nitroglycerin (NTG) administration occurs between 3 and 5-min in adults. The purpose of this study was to identify the time to peak dilation response to sublingual NTG (0.3 mg) in youth. Endothelium-independent dilation (EID) was measured in 198 healthy (113 males, 85 females) youth (6-18 yrs) via ultrasound imaging of the brachial artery following NTG administration up to 5-min. Time to peak EID was 4-min, 28-sec, following NTG administration. There was a significant (p<0.001) difference post-NTG at the 3 vs. 4-min, 4 vs. 5-min, and 3 vs. 5-min time points. Peak EID (males: 24.8 + 0.5 vs. females: 25.3 + 0.6 %, p=0.6) was not significantly different between genders after adjusting for baseline brachial diameter. Endothelium-independent dilation was measured up to 8-min in a small sub-group of 20 youth (12 males, 8 females), resulting in a time to peak dilation of 4-min, 24-sec, and an average change in peak dilation of 23.8 + 1.2 %. No significant difference existed beyond the 4-min time point within the small sub-group. In conclusion, peak response to NTG administration occurred between 4 and 5-min. The results demonstrate the importance of measuring EID up to 5-min post-nitroglycerin administration in youth.
HIFU Monitoring and control With dual-mode ultrasound arrays
(2013-11) Casper, Andrew Jacob
The biological effects of high-intensity focused ultrasound (HIFU) have been known and studied for decades. HIFU has been shown capable of treating a wide variety of diseases and disorders. However, despite its demonstrated potential, HIFU has been slow to gain clinical acceptance. This is due, in part, to the difficulty associated with robustly monitoring and controlling the delivery of the HIFU energy. The non-invasive nature of the surgery makes the assessment of treatment progression difficult, leading to long treatment times and a significant risk of under treatment. This thesis research develops new techniques and systems for robustly monitoring HIFU therapies for the safe and efficacious delivery of the intended treatment. Systems and algorithms were developed for the two most common modes of HIFU delivery systems: single-element and phased array applicators. Delivering HIFU with a single element transducer is a widely used technique in HIFU therapies. The simplicity of a single element offers many benefits in terms of cost and overall system complexity. Typical monitoring schemes rely on an external device (e.g. diagnostic ultrasound or MRI) to assess the progression of therapy. The research presented in this thesis explores using the same element to both deliver and monitor the HIFU therapy. The use of a dual-mode ultrasound transducer (DMUT) required the development of an FPGA based single-channel arbitrary waveform generator and high-speed data acquisition unit. Data collected from initial uncontrolled ablations led to the development of monitoring and control algorithms which were implemented directly on the FPGA. Close integration between the data acquisition and arbitrary waveform units allowed for fast, low latency control over the ablation process. Results are presented that demonstrate control of HIFU therapies over a broad range of intensities and in multiple in vitro tissues. The second area of investigation expands the DMUT research to an ultrasound phased-array. The phased-array allows for electronic steering of the HIFU focus and imaging of the acoustic medium. Investigating the dual-mode ultrasound array (DMUA) required the design and construction of a novel ultrasound-guided focused ultrasound (USgFUS) platform. The platform consisted of custom hardware designed for the unique requirements of operating a phased-array in both therapeutic and imaging modes. The platform also required the development of FPGA based signal processing and GPU based beamforming algorithms for online monitoring of the therapy process. The results presented in this thesis represent the first demonstration of a real-time USgFUS platform based around a DMUA. Experimental imaging and therapy results from series of animal experiments, including a 12 animal GLP study, are presented. In addition, in vitro control results, which build upon the DMUT work, are presented.
Identifying Parameters to Excite or Suppress Peripheral and Central Neurons Using Ultrasound for a New Noninvasive Neuromodulation Approach
(2019-06) Guo, Hongsun
Ultrasound (US) has shown to activate brain circuits, making it a promising noninvasive neuromodulation technique. However, little is known about the underlying mechanisms and neuromodulatory effects across different stimulus parameters. Here, we present research in which we applied transcranial US to different cortical regions and performed brain mapping studies in guinea pigs using extracellular electrophysiology. We observed that US elicits extensive activation across cortical and subcortical brain regions. However, transection of the auditory nerves or removal of cochlear fluids eliminated the US-induced activity, revealing an indirect auditory mechanism for US neural activation. This finding indicates that US stimulation of the brain predominantly activates the ascending auditory system through a cochlear pathway, which can activate other nonauditory regions through cross-modal projections. We then used similar approaches to study US modulatory effects on brain circuits in deafened animals. We observed that US induces localized suppression of somatosensory and visual evoked activity, which is associated with temperature rises in the brain tissue caused by US stimulation. This finding challenges the idea that US non-thermal effects are the only mechanism accounting for suppression of cortical activity by US stimulation. Whereas US activation of brain has been widely reported, activation of peripheral nerves by US have been reported with inconsistent results. Here, we show that US did not directly activate a mammalian sciatic nerve isolated from the surrounding tissue even at high pressures (1.3 to 5 MPa for different transducers) and various pulse patterns, but it could activate sensory structures (e.g., receptors in the skin or surrounding tissue) during stimulation of a non-isolated sciatic nerve, which could be mistakenly interpreted as direct activation of nerves (i.e., activation of the sensory structures leads to activation of peripheral nerves). We further demonstrated that US could reliably suppress nerve activity in vivo, depending on specific pulse durations (PDs), pressures, and center frequencies of US, with the observation that rises in tissue temperature caused by US stimulation drives greater suppressive effects. Maintaining the nerve temperature at a constant level prevents the suppression of nerve activity. These overall findings reveal that US can stimulate sensory structures rather than nerve fibers and that the US thermal effect is a major mechanism for suppression of nerve activity. Further improving our understanding of how US interacts with and modulates receptors, nerve fibers and cells within the brain will facilitate the development of new ultrasound-based neuromodulation therapies for various neurological and psychiatric disorders.
An Investigation of the Cellular Mechanisms Underlying Ultrasound Neuromodulation
(2020-08) Newhoff, Morgan
Focused ultrasound is an emerging neuromodulation technology with the unique potential to noninvasively modulate neuronal activity in deep brain structures with high spatial specificity, offering a potential alternative to invasive neural stimulators. Decades of research have confirmed that ultrasound induces profound effects on neuronal firing rates in a wide range of animal systems, yet the direction (increase or decrease) and primary effector of these effects remain a subject of debate. Here, we describe experiments designed to assess these core questions in a tractable invertebrate model, the medicinal leech (Hirudo verbana). We examined the effects of ultrasound (960 kHz) on an identified motoneuron, a class of cells believed to lack canonical mechanosensitive ion channels, and whose response to ultrasound we predict to be reflective of effects on most neuronal cell types. We observed both neuronal excitation and inhibition, with a bias towards inhibitory effects. These effects were direct, and persisted in the presence of synaptic blockers. Importantly, these effects were only observed when applying ultrasound of sufficient duration to generate heating in excess of 2 °C. Similar durations of ultrasound in a low-heat paradigm were insufficient to induce changes in neuronal firing rate. We thus concluded that heat is the primary effector of ultrasound neuromodulation in this system, which was reinforced by our ability to elicit comparable effects through the targeted application of heat alone. Additional experiments using non-thermal short pulses of ultrasound on sensory neurons failed to produce neuronal activation at and above intensities at which others have reported excitation, with the exception of effects we deemed artifactual due to electrode resonance, and which could be reliably mimicked with micromovements of the recording electrode. We conclude that the mechanical effects of ultrasound, which are frequently described in the literature, are less reliably achieved than thermal effects, and observations ascribed to mechanical effects may be confounded by activation of synaptically-coupled sensory structures or artifact associated with electrode resonance. Nonetheless, ultrasound can generate significant modulation at temperatures < 5 °C, which are believed to be safe for moderate durations. Ultrasound should therefore be investigated as a thermal neuromodulation technology for clinical use.
Magnetoacoustic tomography with magnetic induction for electrical conductivity imaging of biological tissue.
(2010-09) Li, Xu
Electrical properties of biological tissue including conductivity and permittivity play important roles in many biomedical and clinical researches such as modeling neural or cardiac electrical activities and management of electromagnetic energy delivery to the body during clinical diagnosis and treatment. More importantly, these electrical properties may serve as an intrinsic contrast for anatomical or functional imaging. It is therefore of great value to noninvasively image the electrical properties of biological tissue with good accuracy and high spatial resolution. This dissertation research aims at developing and evaluating a new modality i.e. magnetoacoustic tomography with magnetic induction (MAT-MI), for imaging electrical conductivity distribution of biological tissue. In MAT-MI, a conductive object is placed in a static magnetic field and a time-varying magnetic stimulation is applied to induce eddy current inside the object volume. Within the static magnetic field, the Lorentz force acting on the induced eddy current causes mechanical movement of those charged particles in the object and leads to detectable ultrasound signals. These ultrasound signals can be acquired by ultrasound probes and used to reconstruct a high spatial resolution image that indicates the object's electrical conductivity contrast. We have proposed and investigated two types of MAT-MI approaches i.e. single-excitation MAT-MI and multi-excitation MAT-MI. The corresponding image reconstruction algorithms, simulation protocols and experiment systems have been developed for feasibility testing and performance evaluation. It is shown in our computer simulation and experiment studies that using the single-excitation MAT-MI we are able to image the conductivity boundaries of the object with several millimeter spatial resolution. In addition, we have also demonstrated that the multi-excitation MAT-MI approach allows us to further extract the internal information and reconstruct more completely the conductivity contrast of the object. For both approaches, two-dimensional (2D) and three-dimensional (3D) images of physical or tissue phantoms have been acquired and showed promising agreement with the target conductivity distribution. All the results we have collected so far from simulations and experiments suggest that the MAT-MI approach is potential to become an important noninvasive modality for electrical conductivity imaging of biological tissue.
Multiscale Investigation of Low Intensity Transcranial Focused Ultrasound Neuromodulation in in-vivo Rodent Models
(2017-12) Niu, Xiaodan
Transcranial focused ultrasound (tFUS) is a noninvasive neuromodulation method that modulates neural activity using mechanical pressure waves. tFUS has emerged as a promising noninvasive neuromodulation method with millimeter scale resolution and propensity to stimulate deep structures. Researchers have reported tFUS induced short term excitation or inhibition at cortical or deep brain. Currently, there are no reports of long term effects elicited by tFUS. The ability to use tFUS to non-invasively induce long term changes in the brain expands the clinical utility of tFUS. In order to explore the long term effects of tFUS on synaptic connectivity, we first evaluated our setup by examining the ability of tFUS to reliably induce short term changes to in vivo rats. After establishing our setup, we applied pulsed ultrasound to encode temporal information into the hippocampus to induce long term depression in 5 adult rats. Further investigations are needed to explore the underlying mechanisms.
Optimization of ultrasound assisted extraction of cold brewed black tea
(2019-12) Raghunath, Sonali
The tea is a general term used for a beverage that originate from the tea plant, Camellia sinensis. Among different types of teas, black tea is always considered as a rich source of antioxidants, phenolic compounds, essential oils, dietary fiber and other natural bio-actives, which have been shown to exhibit health-promoting effects. Generally, a hot brew is the mechanism of using hot water for brewing the tea leaves. However, application of this technique leads to degradation of flavor and heat sensitive bioactive compounds after being released from the cell membranes. Cold brewing is an alternative method, which can be used to preserve the flavors and other components in the tea. However, application of this method is limited due to the low extraction efficiency and long extraction time. The aim of this project is to evaluate the feasibility of using emerging processing technologies like ultrasonication for improving the extraction of bio-active compounds from black tea and to optimize the processing conditions. This work provides insight on understanding the comparative analysis of OVAT (One variable at a time) vs RSM (Response surface methodology) modeling for cold brewed black tea. This research would make efforts of utilizing alternative process technologies like ultrasound to improve the extraction yield of cold brewed black tea.
Peak shear and peak flow mediated dilation: a time course relationship
(2014-05) Evanoff, Nicholas George
Flow-mediated dilation (FMD) is a measure of endothelial function. This study aimed to explore the temporal relationship of time to peak FMD (FMDTTP) as well as time to peak shear stress (ShearTTP) between children and adults. Shear stress and FMD was assessed in 122 children and 350 adults using ultrasound. A p-value of 0.05 denoted significance. Peak FMD (p=0.022) and Peak Shear rate (p=0.0002), and were significantly larger in children than adults. FMDTTP was significantly slower (p=0.027) in children vs. adults. ShearTTP was slower in children than in adults (p=0.004). There was no significant difference (p=0.27) in time from ShearTTP to FMDTTP between children and adults. In the present showed children not only displayed a larger peak FMD, but also the time it takes the shear stimulus to reach its peak is significantly slower in children than adults. However, the time from peak Shear to peak FMD was similar.
Postoperative Radiotherapy Breast Cancer Treatment: Musculoskeletal and Functional Implications
(2023-09) Braudy, Renata
ABSTRACT Purpose/Hypotheses: The overall purpose of this study was to better understand the effect of post-lumpectomy radiation therapy (RT) on skeletal muscle morphology, shoulder kinematics, and shoulder function following treatment for unilateral breast cancer. We hypothesized that within the same breast cancer survivor, the affected (treated) side would demonstrate significantly different shoulder kinematics and skeletal muscle morphology than the unaffected (untreated) side. We also hypothesized that RT dose delivered to specific muscles within the radiation field would adversely affect self-reported shoulder function. A small study was first performed on healthy volunteers to determine intra-rater reliability of a novel method of skeletal muscle B-mode ultrasonography (US) to evaluate echo intensity (EI) and cross-sectional area (CSA) of three muscles within the radiation field that have the potential to affect shoulder function. Number of Participants: 31 (5 healthy volunteers for US reliability, 26 breast cancer survivors for main study) Materials and Methods: This was a single center, non-therapeutic, observational cross-sectional study with two parts. First, 5 healthy volunteers participated in the US reliability study which involved three repeated measures of the pectoralis major (PMaj), pectoralis minor (PMin), and serratus anterior (SA) bilaterally. Second, 26 breast cancer survivors who were at least 1-year post-completion of RT following lumpectomy plus sentinel lymph node biopsy for the treatment of unilateral breast cancer then participated in the main study. Three-dimensional kinematic data were collected using electromagnetic sensors during forward shoulder flexion and abduction. Musculoskeletal US was used to determine skeletal muscle CSA and EI of the PMaj, PMin, and SA muscles of the treated and untreated sides. Radiation dose analyses were performed for those same 3 muscles using pre-existing computed tomography radiation simulation scans. The Penn Shoulder Score (PSS) and a custom questionnaire were also given to participants. Data were analyzed using Wilcoxon rank sum tests to determine difference across sides and groups, Spearman correlation to examine associations between variables, and multiple linear regression to examine covariate effects. Ultrasound intrarater reliability was performed on the healthy participants using intraclass correlation coefficient (ICC) analysis. Statistical significance cutoff value was set at 0.05 for all tests. Results: PMaj and PMin CSA and EI were reliable (ICC > 0.70) and used in the breast cancer survivor study. SA CSA and EI were not reliable (ICC < 0.7) and were used in the main study as exploratory analyses only. Breast cancer survivors demonstrated more sternoclavicular elevation during arm elevation on their affected side vs. their unaffected side. No significant differences existed between the affected and unaffected sides for other shoulder kinematic variables nor for ultrasound EI and CSA. In general, Penn Shoulder Score values were high, but a few specific functional movements were more commonly noted as being difficult which has clinical implications. Some PMin, PMaj, and SA radiation values were significantly correlated with multiple aspects of the PSS (total score and subscales). Trends were found for the PMin radiation dose and total radiation dose to affect the PSS, although correction for multiple testing made these statistically insignificant. Conclusions: Our data suggests that there may be a significant effect of postoperative RT on shoulder function in breast cancer survivors after unilateral lumpectomy and sentinel lymph node biopsy. Kinematic analysis demonstrated increased clavicle elevation on the affected side vs the unaffected side during arm elevation, but clinical relevance is uncertain. B-mode US was a reliable method of quantifying PMaj and PMin CSA and EI, but it was not reliable for the SA. B-mode US may not be sensitive enough to detect significant differences in EI and CSA in these muscles following RT. The PMaj, PMin, and SA receive a significant amount of radiation during treatment which may affect patient-reported shoulder pain. Although PSS scores were generally high, participants consistently reported ‘some difficulty’ with certain functional tasks that highlight the specific impairments many breast cancer survivors have following treatment. Additionally, breast cancer survivors complained not just of ‘shoulder pain’ but also stiffness, tightness, achiness, and other impairments in their shoulder, chest wall, and arm that need to be recognized and addressed by medical providers. This research demonstrates potential relationships between adjuvant RT and shoulder function which need to be further investigated to provide breast cancer survivors with the highest quality of life possible.
A Single-Element Fiber Transducer for All-Optical Ultrasound and Photoacoustic Sensing
(2019-12) Vilanguppam Thathachary, Supriya
The past few decades have seen a rapid rise in minimally invasive medical procedures performed around the globe. These procedures have been made possible largely because of innovations in medical imaging and sensing to guide physicians in performing the interventions safely. Ultrasound technology has remained highly popular through this transition due to its safety and efficacy. However, the demand for miniature flexible devices for increased accessibility has prompted a shift toward all-optical ultrasound devices. Additionally, photoacoustic imaging and sensing have emerged as a promising technology with abilities to enhance diagnostic capabilities in several clinical applications, most significantly in the imaging of atherosclerotic plaque. The Fabry-perot ultrasound detector, being one of the more widespread optical ultrasound detection technologies, has been explored significantly in this context. This thesis presents a novel wave-guided configuration for fiber Fabry-Perot ultrasound detectors. This work demonstrates 16 times higher sensitivity than traditional piezoelelectric technology at comparable size scales. The chapters that follow present the simulations and experiments conducted around (a) optimizing the fabrication of the wave-guided fiber Fabry-Perot devices, (b) the complete optical and acoustic characterization of the fabricated devices, and (c) the potential improvements that can be made with incorporating dielectric mirrors. The thesis concludes with a discussion on the possible configurations for creating a complete ultrasound and photoacoustic probe for guiding minimally invasive interventions.
Tracking your twin pregnancy using ultrasound
(2012-04-09) Kelley, Kyrsten
Ultrasonic linear array evaluation of concrete pavements
(2013-06) Hoegh, Kyle Edward
Nondestructive evaluation is an important tool for assurance of proper construction practices and selection of rehabilitation procedures for civil infrastructure. Improvements in technology for testing of concrete structures, such as the introduction of dry point contact ultrasonic arrays, allow for collection of repeatable and spatially diverse shear wave impulse time-histories. This dissertation deals with development of methods that can be used for quantitative evaluation of concrete pavement structures using ultrasound linear array systems. The synthetic aperture focusing technique was adapted to handle spatially diverse measurement pairs. Kirchoff migration and the Hilbert transform were utilized to correlate high intensity portions of the instantaneous amplitude time history envelopes to the physical location of changes in acoustic impedance of the tested medium. To mitigate the effect of limited aperture, the interpretation methods were generalized to accommodate virtual array systems and implemented to create two- and three-dimensional reconstructions of the subsurface concrete structure. This reconstruction analysis was applied for practical pavement problems such as reinforcement and layer boundary location, as well as stochastic flaw detection. Comprehensive ground truth validation on several full-scale concrete pavements confirmed the high resolution of the analytical tools developed in this dissertation.
Using Ultrasound to View Your Rotator Cuff.
(2012-07-23) Scheff, Kent
Wrist ganglion cyst: What is it, and what can I do about it?
(2012-07-24) Wilson, Shayla

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