Browsing by Author "Hoyt, Kenneth"
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Item Deep 3D Convolutional Neural Networks for Fast Super-Resolution Ultrasound Imaging(SPIE, 2019-03-15) Brown, Katherine; Dormer, James; Fei, Baowei; Hoyt, Kenneth; Brown, Katherine; Dormer, James; Fei, Baowei; Hoyt, KennethSuper-resolution ultrasound imaging (SR-US) is a new technique which breaks the diffraction limit and can help visualize microvascularity at a resolution of tens of microns. However, image processing methods for spatiotemporal filtering needed in SR-US for microvascular delineation, such as singular value decomposition (SVD), are computationally burdensome and must be performed off-line. The goal of this study was to evaluate a novel and fast method for spatiotemporal filtering to segment the microbubble (MB) contrast agent from the tissue signal with a trained 3D convolutional neural network (3DCNN). In vitro data was collected using a programmable ultrasound (US) imaging system (Vantage 256, Verasonics Inc, Kirkland, WA) equipped with an L11-4v linear array transducer and obtained from a tissue-mimicking vascular flow phantom at flow rates representative of microvascular conditions. SVD was used to detect MBs and label the data for training. Network performance was validated with a leave-one-out approach. The 3DCNN demonstrated a 22% higher sensitivity in MB detection than SVD on in vitro data. Further, in vivo 3DCNN results from a cancer-bearing murine model revealed a high level of detail in the SR-US image demonstrating the potential for transfer learning from a neural network trained with in vitro data. The preliminary performance of segmentation with the 3DCNN was encouraging for real-time SR-US imaging with computation time as low as 5 ms per frame.Item Hyposialylated IgG Activates Endothelial IgG Receptor FcγRIIB to Promote Obesity-Induced Insulin Resistance(American Society for Clinical Investigation, 2018-11-05) Tanigaki, K.; Sacharidou, A.; Peng, J.; Chambliss, K. L.; Yuhanna, I. S.; Ghosh, Debabrata; Ahmed, M.; Szalai, A. J.; Vongpatanasin, W.; Mattrey, R. F.; Chen, Q.; Azadi, P.; Lingvay, I.; Botto, M.; Holland, W. L.; Kohler, J. J.; Sirsi, Shashank R.; Hoyt, Kenneth; Shaul, P. W.; Mineo, C.; Ghosh, Debabrata; Sirsi, Shashank R.; Hoyt, KennethType 2 diabetes mellitus (T2DM) is a common complication of obesity. Here, we have shown that activation of the IgG receptor FcγRIIB in endothelium by hyposialylated IgG plays an important role in obesity-induced insulin resistance. Despite becoming obese on a high-fat diet (HFD), mice lacking FcγRIIB globally or selectively in endothelium were protected from insulin resistance as a result of the preservation of insulin delivery to skeletal muscle and resulting maintenance of muscle glucose disposal. IgG transfer in IgG-deficient mice implicated IgG as the pathogenetic ligand for endothelial FcγRIIB in obesity-induced insulin resistance. Moreover, IgG transferred from patients with T2DM but not from metabolically healthy subjects caused insulin resistance in IgG-deficient mice via FcγRIIB, indicating that similar processes may be operative in T2DM in humans. Mechanistically, the activation of FcγRIIB by IgG from obese mice impaired endothelial cell insulin transcytosis in culture and in vivo. These effects were attributed to hyposialylation of the Fc glycan, and IgG from T2DM patients was also hyposialylated. In HFD-fed mice, supplementation with the sialic acid precursor N-acetyl-D-mannosamine restored IgG sialylation and preserved insulin sensitivity without affecting weight gain. Thus, IgG sialylation and endothelial FcγRIIB may represent promising therapeutic targets to sever the link between obesity and T2DM.Item Impact of Hydrostatic Pressure on Phase-Change Contrast Agent Activation by Pulsed Ultrasound(Acoustical Society of America, 2019-06-14) Raut, Saurabh; Khairalseed, Mawia; Honari, Arvin; Sirsi, Shashank R.; Hoyt, Kenneth; Raut, Saurabh; Khairalseed, Mawia; Honari, Arvin; Sirsi, Shashank R.; Hoyt, KennethA phase-change contrast agent (PCCA) can be activated from a liquid (nanodroplet) state using pulsed ultrasound (US) energy to form a larger highly echogenic microbubble (MB). PCCA activation is dependent on the ambient pressure of the surrounding media, so any increase in hydrostatic pressure demands higher US energies to phase transition. In this paper, the authors explore this basic relationship as a potential direction for noninvasive pressure measurement and foundation of a unique technology the authors are developing termed tumor interstitial pressure estimation using ultrasound (TIPE-US). TIPE-US was developed using a programmable US research scanner. A custom scan sequence interleaved pulsed US transmissions for both PCCA activation and detection. An automated US pressure sweep was applied, and US images were acquired at each increment. Various hydrostatic pressures were applied to PCCA samples. Pressurized samples were imaged using the TIPE-US system. The activation threshold required to convert PCCA from the liquid to gaseous state was recorded for various US and PCCA conditions. Given the relationship between the hydrostatic pressure applied to the PCCA and US energy needed for activation, phase transition can be used as a surrogate of hydrostatic pressure. Consistent with theoretical predictions, the PCCA activation threshold was lowered with increasing sample temperature and by decreasing the frequency of US exposure, but it was not impacted by PCCA concentration. © 2019 Acoustical Society of America.Item Monitoring Acute Changes in Pancreatic Tumor Perfusion with Contrast-Enhanced Ultrasound and Photoacoustic Imaging Following Targeted Hyaluronic Acid Treatment(2020-05) Javed, Kulsoom; Hoyt, KennethPancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer related deaths. Early diagnosis is crucial for treating PDAC but is unlikely due to the asymptomatic nature of the tumor in early stages. PDAC is usually diagnosed in late stages when it cannot be resected and is not responsive to chemotherapy (chemoresistance). The chemoresistance and late symptoms are mostly due to the presence of hyaluronan (HA, glycosaminoglycan) in the extracellular matrix (ECM). HA is a marker of tumor aggression and is hydrophilic. It retains water molecules and forms a gel-fluid phase which increases the tumor interstitial pressure, collapses the tumor microvasculature, and causes chemoresistance. HA can be degraded by an enzyme, pegylated pancreatic hyaluronidase (PEGPH20; targeted HA treatment), into its subunits. The aim of this study was to monitor the acute changes in tumor perfusion with contrast enhanced ultrasound and photoacoustic imaging following HA removal by PEGPH20. Athymic nude mice (N=18) were implanted subcutaneously in the peri-tibial region of the right leg with 2 million pancreatic cancer cells. Contrast enhanced ultrasound (CEUS) and photoacoustic (PA) imaging studies were conducted at baseline (0 h) and at 6 h. A single dose of PEGPH20 (treatment) or saline (control) was injected at baseline. After the targeted removal of HA by PEGPH20, the tumor microvasculature expanded and an increase in tumor perfusion parameters; peak enhancement (PE) and wash-in rate (WiR) measured by CEUS, and total hemoglobin signal (HbT) and oxygen saturation (sO2) measured by PA was seen. These changes in CEUS and PA measures were confirmed by histological analysis of the excised tumor tissue. In conclusion, we saw a 50% increase in perfusion parameters at 6 h post treatment as compared to the control group. These acute changes in pancreatic tumor tissue can be monitored noninvasively by CEUS and PA imaging within 6 h of HA removal by PEGPH20.Item Monitoring Early Breast Cancer Response To Neoadjuvant Therapy Using H-Scan Ultrasound Imaging: Preliminary Preclinical Results(John Wiley and Sons Ltd., 2019-04-17) Khairalseed, Mawia; Javed, Kulsoom; Jashkaran, G.; Kim, J. -W; Parker, K. J.; Hoyt, Kenneth; Hoyt, Kenneth; Khairalseed, Mawia; Javed, KulsoomObjective—H-scan imaging is a new ultrasound technique used to visualize the relative size of acoustic scatterers. The purpose of this study was to evaluate the use of H-scan ultrasound imaging for monitoring early tumor response to neoadjuvant treatment using a preclinical breast cancer animal model. Methods—Real-time H-scan ultrasound imaging was implemented on a programmable ultrasound scanner (Vantage 256; Verasonics Inc., Kirkland, WA) equipped with an L11-4v transducer. Bioluminescence and H-scan ultrasound was used to image luciferase-positive breast cancer–bearing mice at baseline and at 24, 48, and 168 hours after administration of a single dose of neoadjuvant (paclitaxel) or sham treatment. Animals were euthanized at 48 or 168 hours, and tumors underwent histologic processing to identify cancer cell proliferation and apoptosis. Results—Baseline H-scan ultrasound images of control and therapy group tumors were comparable, but the latter exhibited significant changes over the 7-day study (P 0.40, P < .04). Conclusion—Preliminary preclinical results suggest that H-scan ultrasound imaging is a new and promising tissue characterization modality. H-scan ultrasound imaging may provide prognostic value when monitoring early tumor response to neoadjuvant treatment. © 2018 by the American Institute of Ultrasound in Medicine.Item Morphological Image Processing for Multiscale Analysis of Super-Resolution Ultrasound Images of Tissue Microvascular Networks(SPIE-Int Soc Optical Engineering, 2019-03-15) Özdemir, Ipek; Hoyt, Kenneth; Özdemir, Ipek; Hoyt, KennethDiabetes is a major disease and known to impair microvascular recruitment due to insulin resistance. Previous quantifications of the changes in microvascular networks at the capillary level were being performed with either full or manually selected region-of-interests (ROIs) from super-resolution ultrasound (SR-US) images. However, these approaches were imprecise, time-consuming, and unsuitable for automated processes. Here we provided a custom software solution for automated multiscale analysis of SR-US images of tissue microvascularity patterns. An Acuson Sequoia 512 ultrasound (US) scanner equipped with a 15L8-S linear array transducer was used in a nonlinear imaging mode to collect all data. C57BL/6J male mice fed standard chow and studied at age 13-16 wk comprised the lean group (N = 14), and 24-31 wk-old mice who received a high-fat diet provided the obese group (N = 8). After administration of a microbubble (MB) contrast agent, the proximal hindlimb adductor muscle of each animal was imaged (dynamic contrast-enhanced US, DCE-US) for 10 min at baseline and again at 1 h and towards the end of a 2 h hyperinsulinemic-euglycemic clamp. Vascular structures were enhanced with a multiscale vessel enhancement filter and binary vessel segments were delineated using Otsu's global threshold method. We then computed vessel diameters by employing morphological image processing methods for quantitative analysis. Our custom software enabled automated multiscale image examination by defining a diameter threshold to limit the analysis at the capillary level. Longitudinal changes in AUC, I_{PK}, and MVD were significant for lean group (p < 0.02 using Full-ROI and p < 0.01 using 150 μm-ROI) and for obese group (p < 0.02 using Full-ROI, p < 0.03 using 150 μm-ROI). By eliminating large vessels from the ROI (above 150 μm in diameter), perfusion parameters were more sensitive to changes exhibited by the smaller vessels, that are known to be more impacted by disease and treatment.Item Non-Invasive Pressure Estimation Using Ultrasound Imaging and Phase Change Contrast Agents(2020-05) Raut, Saurabh Vikas; Hoyt, KennethPulsed ultrasound (US) energy can be used to activate a phase-change contrast agent (PCCA) from a liquid nanodroplet state to form a larger highly echogenic microbubble (MB). PCCA activation is dependent on the ambient pressure, and temperature of the surrounding media, applied frequency of the US transducer, and size of the PCCA. This research explores the relationship of these parameters on the activation threshold as a potential non-invasive pressure measurement and foundation for a unique technology our research group is developing termed tumor interstitial pressure estimation using ultrasound (TIPE-US). This thesis outlines development of TIPE-US using a programmable US research scanner for both PCCA activation and MB detection. An automated pressure sweep was applied to acquire US images at each hydrostatic pressure increment. The activation threshold required to convert PCCA from liquid to gaseous state was recorded for various hydrostatic pressures (10 to 100 mmHg) applied to PCCA samples and the effect of aforementioned parameters were demonstrated. Consistent with theoretical predictions, the PCCA activation threshold was lowered with increasing temperature and by decreasing the frequency of US exposure, but it was not impacted by PCCA concentration. Although, theoretically the activation threshold decreases as diameter of the PCCA increases, experimentally this effect was not discernible.Item Novel Method for the Formation of Monodisperse Superheated Perfluorocarbon Nanodroplets as Activatable Ultrasound Contrast Agents(Royal Society of Chemistry, 2018-08-20) De, Gracia Lux; Vezeridis, A. M.; Lux, J.; Armstrong, A. M.; Sirsi, Shashank R.; Hoyt, Kenneth; Mattrey, R. F.; Sirsi, Shashank R.; Hoyt, KennethMicrobubble (MB) contrast agents have positively impacted the clinical ultrasound (US) community worldwide. Their use in molecular US imaging applications has been hindered by their limited distribution to the vascular space. Acoustic droplet vaporization (ADV) of nanoscale superheated perfluorocarbon nanodroplets (NDs) demonstrates potential as an extravascular contrast agent that could facilitate US-based molecular theranostic applications. However these agents are metastable and difficult to manufacture with high yields. Here, we report a new formulation technique that yields reliable, narrowly dispersed sub-300 nm decafluorobutane (DFB) or octafluoropropane (OFP)-filled phospholipid-coated NDs that are stable at body temperature, using small volume microfluidization. Final droplet concentration was high for DFB and lower for OFP (>10¹² vs. >10¹⁰ NDs per mL). Superheated ND stability was quantified using tunable resistive pulse sensing (TRPS) and dynamic light scattering (DLS). DFB NDs were stable for at least 2 hours at body temperature (37 °C) without spontaneous vaporization. These NDs are activatable in vitro when exposed to diagnostic US pressures delivered by a clinical system to become visible microbubbles. The DFB NDs were sufficiently stable to allow their processing into functionalized NDs with anti-epithelial cell adhesion molecule (EpCAM) antibodies to target EpCAM positive cells.Item Novel Ultrasound Imaging Methods for the Characterization of Tissue Microvascular Networks(2021-04-27) Ozdemir, Ipek; Hoyt, KennethThe structure and function of tissue microcirculation are critical in most major disease developments and in the patient-specific treatment response. Adequate quantitative characterization of tissue microvasculature may therefore assist to better understand various types of disorders, to develop new therapeutic strategies, and to monitor early response to therapy. Currently, the greatest challenge is to accurately and precisely quantify the microvascular properties in a noninvasive manner. To address this challenge, this dissertation proposes characterizing the tissue microvascular network morphology using contrast-enhanced ultrasound (CEUS). We hypothesize that the development of morphological image analysis methods using CEUS images will improve in vivo quantitative analysis of tissue microvascular networks for early treatment monitoring. This work demonstrates (1) the potential of CEUS-derived morphological features as a predictor of anti-cancer therapy response, (2) the development and use of multiparametric CEUS image analysis, and (3) the implementation of three-dimensional superresolution US visualization and quantification using advanced image analysis methods.Item Open Source Software Solution for Advance Image Processing of Ultrasound Images(2017-12) Dsouza, Deandra Janice; Hoyt, KennethCancer is the second leading cause of death, in the United States. An estimate of 255,180 new cases of breast cancer are expected in 2017. The number of deaths due to breast cancer for women are estimated to exceed 40,000 in this same year [1]. National expenditures for cancer care in the United States totaled nearly $125 billion in 2010 and could reach $156 billion in 2020 [2]. As a predominantly age-linked disease, these Figures are expected to rise with increasing population life expectancy. Improvements in noninvasive early cancer detection or monitoring treatment would greatly help in the way therapy is delivered to cancer patients. DCE-US imaging has shown potential in helping oncologists in the management of patients diagnosed with, and treated for, cancer. When exposed to US, intravascular MB contrast agents produce a unique signal compared to the surrounding tissue. These unique signals can be isolated and used to give valuable insight into the tumor angiogenic network helping support cancer growth. Current software packages for analyzing DCE-US images are costly and have limited accessibility to the research community. Thus, there is a growing demand for a more widespread and cost-effective solution to help analyze tumor angiogenic properties. To that end, a custom open-source software solution for processing DCE-US images was developed during this thesis project. This new Matlab-based software can be used to characterize the perfusion properties associated with tumor growth and quantify any changes related to drug treatment response (or lack thereof). We hypothesize that this new image processing tool will develop into an asset in personalized medicine and positively impact cancer management.Item Pentagalloyl Glucose and Its Functional Role in Vascular Health: Biomechanics and Drug-Delivery Characteristics(Springer, 2018-10-08) Patnaik, Sourav S.; Simionescu, Dan T.; Goergen, Craig J.; Hoyt, Kenneth; Sirsi, Shashank; Finol, Ender A.; Hoyt, Kenneth; Sirsi, ShashankPentagalloyl glucose (PGG) is an elastin-stabilizing polyphenolic compound that has significant biomedical benefits, such as being a free radical sink, an anti-inflammatory agent, anti-diabetic agent, enzymatic resistant properties, etc. This review article focuses on the important benefits of PGG on vascular health, including its role in tissue mechanics, the different modes of pharmacological administration (e.g., oral, intravenous and endovascular route, intraperitoneal route, subcutaneous route, and nanoparticle based delivery and microbubble-based delivery), and its potential therapeutic role in vascular diseases such as abdominal aortic aneurysms (AAA). In particular, the use of PGG for AAA suppression and prevention has been demonstrated to be effective only in the calcium chloride rat AAA model. Therefore, in this critical review we address the challenges that lie ahead for the clinical translation of PGG as an AAA growth suppressor.Item Signal Processing Algorithms for Smartphone-Based Hearing Aid Platform; Applications and Clinical Testing(2022-05-01T05:00:00.000Z) Tokgoz, Serkan; Panahi, Issa M.S.; Hoyt, Kenneth; Thibodeau, Linda M.; Kiasaleh, Kamran; Tamil, LakshmanDigital signal processing algorithms are widely utilized in hearing aid applications to im- prove the quality of speech. The signal processing pipeline for speech involves several crucial components that enhance hearing-impaired people’s listening. This thesis covers the devel- opment of novel methods that can be used in the speech processing pipeline and clinical testing. Each chapter of the dissertation focuses on the components of the speech process- ing pipeline for smartphone-based hearing aid setup. The first algorithm, speech source localization (SSL), which identifies the direction of the talker of interest using multiple mi- crophones, is discussed. A speaker identification method is proposed as an assistive system to the pipeline, and it can be used to boost the overall system’s performance. A clinical testing system is developed to evaluate the new signal processing algorithms. An approach is developed to use multiple microphones of iPhone simultaneously for real-time low-latency audio applications. Real-time integration of several signal processing modules that appear in digital hearing aids is developed as smartphone apps. Subjective evaluations are conducted for the proposed methods to show noticeable improvements and compared with state of the art methods. Additionally, the implementation of the proposed methods is explained on smartphones and computers.Item Spatial Angular Compounding Technique for H-Scan Ultrasound Imaging.(2018-10-22) Khairalseed, Mawia; Xiong, Fangyuan; Kim, Jung-whan; Mattrey, Robert F.; Parker, Kevin J.; Hoyt, Kenneth; Khairalseed, Mawia; Xiong, Fangyuan; Kim, Jung-whan; Hoyt, KennethH-Scan is a new ultrasound imaging technique that relies on matching a model of pulse-echo formation to the mathematics of a class of Gaussian-weighted Hermite polynomials. This technique may be beneficial in the measurement of relative scatterer sizes and in cancer therapy, particularly for early response to drug treatment. Because current H-scan techniques use focused ultrasound data acquisitions, spatial resolution degrades away from the focal region and inherently affects relative scatterer size estimation. Although the resolution of ultrasound plane wave imaging can be inferior to that of traditional focused ultrasound approaches, the former exhibits a homogeneous spatial resolution throughout the image plane. The purpose of this study was to implement H-scan using plane wave imaging and investigate the impact of spatial angular compounding on H-scan image quality. Parallel convolution filters using two different Gaussian-weighted Hermite polynomials that describe ultrasound scattering events are applied to the radiofrequency data. The H-scan processing is done on each radiofrequency image plane before averaging to get the angular compounded image. The relative strength from each convolution is color-coded to represent relative scatterer size. Given results from a series of phantom materials, H-scan imaging with spatial angular compounding more accurately reflects the true scatterer size caused by reductions in the system point spread function and improved signal-to-noise ratio. Preliminary in vivo H-scan imaging of tumor-bearing animals suggests this modality may be useful for monitoring early response to chemotherapeutic treatment. Overall, H-scan imaging using ultrasound plane waves and spatial angular compounding is a promising approach for visualizing the relative size and distribution of acoustic scattering sources.Item Super-Resolution Ultrasound Imaging of Microvascular Networks(2021-05-03) Brown, Katherine G.; Hoyt, KennethUnder development in a pre-clinical setting, super-resolution ultrasound (SR-US) imaging brings up to a ten-fold improvement in ultrasound (US) resolution. It can image microvascular changes in various disease processes including cancer, diabetes, and cardiovascular disease. Barriers to the clinical use of SR-US include the heavy computational burden of both detecting and localizing the microbubble (MB) contrast agent, as well as lengthy US imaging times longer than a breath hold. The long computation time of minutes or hours requires the use of offline processing and precludes the use of SR-US as a real-time imaging modality which is viewed as a major advantage of US imaging. We hypothesize that the use nonlinear multi-pulse sequences will improve the numbers of MBs detected per frame and reduce image acquisition time for SR-US towards a comfortable breath-hold length for the patient. We further hypothesize that the use of deep learning algorithms can begin to enable a real-time SR-US imaging modality by the reduction of computation time by several orders of magnitude. In this dissertation work we demonstrate: (1) improved MB detection in SR-US with the use of nonlinear US pulse sequences to enhance the contrast of MBs with tissue, (2), improve performance of super-resolution processing with deep learning for MB detection and precise localization, and (3) equivalent performance of deep learning methods to current methods in the assessment of tumor treatment by monitoring any microvessel changes.Item Tissue Characterization Using H-scan Ultrasound Imaging(2022-12-01T06:00:00.000Z) Tai, Haowei 1991-; Hoyt, Kenneth; Griffith, D. Todd; Brown, Katherine; Hansen, John H.L.; Tamil, LakshmanBreast cancer is the second leading cause of mortality among women and affects more women than any other type of cancer. Around 43,600 women in the U.S. died in 2021 from breast cancer. Clinical studies have demonstrated that an early neoadjuvant response is a better predictor of the patient’s recurrence-free survival than pathological complete response. Therefore, mammography, ultrasound (US), and magnetic resonance imaging (MRI) have been widely used to determine tumor response by tracking changes in tumor size using guidelines provided by the Response Evaluation Criteria in Solid Tumors (RECIST). However, measurable changes in tumor size may not be detectable until after multiple cycles of chemotherapy. In the interim, high cost and unnecessary patient toxicity may be incurred for therapy regimens. Further, intratumor heterogeneity poses a fundamental treatment challenge because different tumor subregions might have different drug sensitivities. This implies that some therapeutic strategies might not be effective against the whole tumor. Therefore, the use of noninvasive US for quantitative tissue characterization has become an exciting research prospect. Herein the challenge is to find hidden patterns in the US data to reveal more information about tissue function and pathology that cannot be seen in the conventional US images. Circumventing some of the limitations associated with traditional tissue characterization approaches, a new modality has been proposed for the US classification of acoustic scatterers, such as cancer cells. Termed H-scan US imaging, this technique relies on matching a model that describes US image formation to the mathematics of a class of Gaussian-weighted Hermite polynomials. In short, it reveals the local frequency dependence of different sized scatterers in soft tissue. In this dissertation work we demonstrate: (1) application of a novel frequency-dependent attenuation correction technique improves H-scan US imaging sensitivity to subtle changes at tissue depth. (2) propose 3-D H-scan imaging technique to capture data from the entire tumor burden, visualization of any heterogenous tissue patterns, and fundamentally improve any tissue characterization strategy and treatment response determination and (3) propose volumetric H-scan US imaging to visualize breast cancer changes during response to drug treatment including apoptotic activity, which is a hallmark feature of effective anticancer therapy. Our overarching hypothesis is that volumetric H-scan US imaging can detect early response to chemotherapy in breast cancer tumors and provide vital prognostic data on treatment response and tumor progression. Consequently, this would provide a new and safe approach to exploring the tumor response to chemotherapy as early as possible and maximize effective therapy for an individual patient, reduce morbidity, and constrain escalating health care costs associated with overtreatment.Item Two-Dimensional Temperature Imaging Using Diagnostic Ultrasound—Preliminary in Vitro Studies Using Phantom Materials(2018-12) Dolui, Swapnil; Hoyt, KennethTemperature monitoring plays an important role during thermal therapy. Ultrasound (US) can be used to estimate the temperature, and the current approach is based on detection of the change in instantaneous frequency of reflected US signals along the US axial beam direction. In this thesis, a novel US-based temperature estimation technique has been proposed that improves on the current method by filtering the reflected US signals with Gaussian-weighted nth-order Hermite (GHn) polynomial function. In vitro experiments were conducted by slowly heating a series of tissue-mimicking phantom materials that were fabricated using hydrogel that were embedded with different-sized US scatterers. Overall, our US-based temperature mapping technique exhibited a 17.4% improvement in measurement accuracy compared to an established US imaging approach.Item Ultrasound Sensing of Lower-limb Skeletal Muscle and the Potential for Robotic Assistive Device Control(2022-05-01T05:00:00.000Z) Jahanandish, Hassan; Hoyt, Kenneth; Hao, Shuang; Dhaher, Yasin; Kang, Gu Eon; Brown, KatherineAn estimated 11% of the world's population either faces difficulty with daily mobility or uses assistive devices such as walkers, canes, crutches, and wheelchairs, reducing the quality of life and impairing the independence of their living. Lower-limb robotic assistive devices such as prosthetic limbs and exoskeletons hold a great promise to improve the quality of life of these individuals by replicating most of the actions of healthy biological limbs. However, the clinical translation and widespread adoption of these devices are still hindered by the lack of control intuitiveness and continuous adaptation to user intentions. Ultrasound is a noninvasive sensing modality that can access human neuromuscular information by measuring muscle activation and contraction. Hence, the objective of the present dissertation was to investigate the feasibility of using the ultrasound sensing modality as a wearable human-machine interface for lower-limb robotic assistive devices. We hypothesize that human lower-limb muscle kinematics and kinetics, noninvasively tracked by ultrasound sensing, can be used to estimate continuous lower-limb joint movements. We further hypothesize that ultrasound sensing can be used as a sensing interface with a continuous volitional control framework to integrate with lower-limb robotic assistive devices. In this dissertation, we: 1) develop a framework to extract muscle contraction features from ultrasound images demonstrate their use for lower-limb joint motion estimation, 2) develop an ultrasound-based control framework for continuous joint-level control of lower-limb assistive devices during various steady-state and non-steady-state ambulation modes, and 3) improve the potential integration of the ultrasound technology with existing lower-limb assistive devices by reducing the integrationlimiting parameters of the current ultrasound technology. The outcomes of this dissertation may eventually enhance the clinical relevance of lower-limb robotic assistive devices and facilitate their widespread adoption for the population with mobility problems.