305 research outputs found
Integrated Electronics for Wireless Imaging Microsystems with CMUT Arrays
Integration of transducer arrays with interface electronics in the form of single-chip CMUT-on-CMOS has emerged into the field of medical ultrasound imaging
and is transforming this field. It has already been used in several commercial products such as handheld full-body imagers and it is being implemented by commercial and academic groups for Intravascular Ultrasound and Intracardiac Echocardiography. However, large attenuation of ultrasonic waves transmitted through
the skull has prevented ultrasound imaging of the brain. This research is a prime
step toward implantable wireless microsystems that use ultrasound to image the
brain by bypassing the skull. These microsystems offer autonomous scanning
(beam steering and focusing) of the brain and transferring data out of the brain for
further processing and image reconstruction.
The objective of the presented research is to develop building blocks of an integrated electronics architecture for CMUT based wireless ultrasound imaging systems while providing a fundamental study on interfacing CMUT arrays with their
associated integrated electronics in terms of electrical power transfer and acoustic
reflection which would potentially lead to more efficient and high-performance
systems.
A fully wireless architecture for ultrasound imaging is demonstrated for the
first time. An on-chip programmable transmit (TX) beamformer enables phased
array focusing and steering of ultrasound waves in the transmit mode while its
on-chip bandpass noise shaping digitizer followed by an ultra-wideband (UWB)
uplink transmitter minimizes the effect of path loss on the transmitted image data
out of the brain. A single-chip application-specific integrated circuit (ASIC) is de-
signed to realize the wireless architecture and interface with array elements, each
of which includes a transceiver (TRX) front-end with a high-voltage (HV) pulser,
a high-voltage T/R switch, and a low-noise amplifier (LNA). Novel design techniques are implemented in the system to enhance the performance of its building
blocks.
Apart from imaging capability, the implantable wireless microsystems can include a pressure sensing readout to measure intracranial pressure. To do so, a
power-efficient readout for pressure sensing is presented. It uses pseudo-pseudo
differential readout topology to cut down the static power consumption of the sensor for further power savings in wireless microsystems.
In addition, the effect of matching and electrical termination on CMUT array
elements is explored leading to new interface structures to improve bandwidth
and sensitivity of CMUT arrays in different operation regions. Comprehensive
analysis, modeling, and simulation methodologies are presented for further investigation.Ph.D
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High frame-rate pulse wave imaging for non-invasive characterization of arterial stiffness in vivo
Recent studies have indicated that vascular stiffness is an important predictor of future cardiovascular disease. Hence, assessment of vascular stiffness would be of interest. Ultrasound is a good modality for assessment of vascular stiffness, due to its hight temporal resolution and non-invasive nature. Using ultrasound, various techniques have been proposedto estimate vascular stiffness, one of them being Pulse Wave Imaging. The ultimate goal of Pulse Wave Imaging is to provide a robust, qualitative and quantitative method to estimate and visualize clinically important parameters and phenomenonfor cardiovascular disease. The objective of this thesis limits itself to 1) expand Pulse Wave Imaging by going beyond just the diastolic stiffness, 2) utilize Pulse Wave Imaging in an atherosclerotic swine model to monitor plaque initiation and progression and 3) improve non-linear stiffness estimation at or near sites of reflections using Pulse Wave Imaging for clinical applications.
In Aim 1, the question pursued was whether Pulse Wave Imaging can be utilized to monitor this non-linear behavior in-vivo. It was observed that in this mouse model, the compliance at diastolic pressure did not change significantly, whereas the compliance at end-systole did. Thus suggesting that Pulse Wave Imaging was able to monitor a change in non-linear stiffness, and that considering this, might be of importance.
In Aim 2, the ability of Pulse Wave Imaging to monitor disease progression for atherosclerotic disease progression was assessed. Since human studies involve various compounding factors, animal models provide the opportunity to study the ability of methods in a more controlled manner. Swine is a good candidate due to its similarity with humans. To doso, first, the feasibility of Pulse Wave Imaging in swine needed to be assessed. While the cardiovascular system might be similar, various other factors, such as the location and depth of the carotid differs. It was revealed that PWI was feasible in swine and that we were able to generate atherosclerotic lesions within 9-months. Subsequently the ability of Pulse Wave Imaging and Vector Flow Imaging to monitor atherosclerotic progression leading to different type of lesions was assessed. The in-vivo findings were compared with histology and nanoidentation. The results indicated that Pulse Wave Imaging was shown to be able to separate to different disease progression pathways leading to different type of lesions.
Finally in Aim 3, lessons learned from the animal models were attempted to be addressed by developing a more reflection robust approach for localized non-linear stiffness estimation for clinical application. First, improvements were proposed to a previously developed inverse problem approach that can resolve reflections within the field of view by including information from the flow velocity. To expand the approach to include non-linearity and reflections that occur outside the field of view, a physics-based neural network approach was considered. This might be of importance since most plaques are located at sites of significant reflections, such as the bifurcation. Chapter 6 revealed that artificial significant sources of reflections hindered its ability for sub-cm scale localized compliance measurements as indicated by an immediate increase in the number of detected segments after the ligation was induced. The approaches was validated using simulated data and feasibility was shown in in-vivo examples. With new progress, new issues tend to arise.
Finally, the purpose of this sub-aim is to utilize the technique and investigate whether or not it can in fact better differentiate between different clinically relevant groups. The findings revealed no significant improvement concerning the mean compliance estimated, but appeared more robust against outliers when only the plaque segment was assessed.
In conclusion, the results shown in this dissertation indicate that Pulse Wave Imaging is a promising approach to assess non-linear stiffness estimation for monitoring of vascular disease. Furthermore, an new methodology was proposed and feasibility was shown, which could further improve localized and non-linear stiffness estimation at or near sources of significant reflections, and which can be used as a starting point for further development
Advanced Photothermal Optical Coherence Tomography (PT-OCT) for Quantification of Tissue Composition
Optical coherence tomography (OCT) is an imaging technique that forms 2D or 3D images of tissue structures with micron-level resolution. Today, OCT systems are widely used in medicine, especially in the fields of ophthalmology, interventional cardiology, oncology, and dermatology. Although OCT images provide insightful structural information of tissues, these images are not specific to the chemical composition of the tissue. Yet, chemical tissue composition is frequently relevant to the stage of a disease (e.g., atherosclerosis), leading to poor diagnostic performance of structural OCT images.
Photo-thermal optical coherence tomography (PT-OCT) is a functional extension of OCT with the potential to overcome this shortcoming by overlaying the 3D structural images of OCT with depth-resolved light absorption information. Potentially, signal analysis of the light absorption maps can be used to obtain refined insight into the chemical composition of tissue. Such analysis, however, is complex because the underlying physics of PT-OCT is multifactorial. Aside from tissue chemical composition, the optical, thermal, and mechanical properties of tissue affect PT-OCT signals; system/instrumentation parameters also influence PT-OCT signals. As such, obtaining refined insight into tissue chemical composition requires in-depth research aimed at answering several key unknowns and questions about this technique.
The goal of this dissertation is to generate in-depth knowledge on sample and system parameters affecting PT-OCT signals, to develop strategies for optimal detection of a molecule of interest (MOI) and potentially for its quantification, and to improve the imaging rate of the system. The following items are major outcomes of this dissertation:
1- Generated comprehensive theory that discovers relations between sample/tissue properties and experimental conditions and their multifactorial effects on PT-OCT signals.
2- Developed system and experimentation strategies for detection of multiple molecules of interest with high specificity.
3- Generated optimized machine learning-powered model, in light of the above two outcomes, for automated depth-resolved interpretation of tissue composition from PT-OCT images.
4- Increased the imaging rate of PT-OCT by orders of magnitude by introducing a new variant of PT-OCT based on pulsed photothermal excitation.
5- Developed algorithms for signal denoising and improving the quality of received signals and the contrast in images which in return enables faster PT-OCT imaging
Photoacoustic Imaging in Biomedicine and Life Sciences
Photo-acoustic imaging, also known as opto-acoustic imaging, has become a widely popular modality for biomedical applications. This hybrid technique possesses the advantages of high optical contrast and high ultrasonic resolution. Due to the distinct optical absorption properties of tissue compartments and main chromophores, photo-acoustics is able to non-invasively observe structural and functional variations within biological tissues including oxygenation and deoxygenation, blood vessels and spatial melanin distribution. The detection of acoustic waves produced by a pulsed laser source yields a high scaling range, from organ level photo-acoustic tomography to sub-cellular or even molecular imaging. This review discusses significant novel technical solutions utilising photo-acoustics and their applications in the fields of biomedicine and life sciences
Advanced Photothermal Optical Coherence Tomography (PT-OCT) for Quantification of Tissue Composition
Optical coherence tomography (OCT) is an imaging technique that forms 2D or 3D images of tissue structures with micron-level resolution. Today, OCT systems are widely used in medicine, especially in the fields of ophthalmology, interventional cardiology, oncology, and dermatology. Although OCT images provide insightful structural information of tissues, these images are not specific to the chemical composition of the tissue. Yet, chemical tissue composition is frequently relevant to the stage of a disease (e.g., atherosclerosis), leading to poor diagnostic performance of structural OCT images.
Photo-thermal optical coherence tomography (PT-OCT) is a functional extension of OCT with the potential to overcome this shortcoming by overlaying the 3D structural images of OCT with depth-resolved light absorption information. Potentially, signal analysis of the light absorption maps can be used to obtain refined insight into the chemical composition of tissue. Such analysis, however, is complex because the underlying physics of PT-OCT is multifactorial. Aside from tissue chemical composition, the optical, thermal, and mechanical properties of tissue affect PT-OCT signals; system/instrumentation parameters also influence PT-OCT signals. As such, obtaining refined insight into tissue chemical composition requires in-depth research aimed at answering several key unknowns and questions about this technique.
The goal of this dissertation is to generate in-depth knowledge on sample and system parameters affecting PT-OCT signals, to develop strategies for optimal detection of a molecule of interest (MOI) and potentially for its quantification, and to improve the imaging rate of the system. The following items are major outcomes of this dissertation:
1- Generated comprehensive theory that discovers relations between sample/tissue properties and experimental conditions and their multifactorial effects on PT-OCT signals.
2- Developed system and experimentation strategies for detection of multiple molecules of interest with high specificity.
3- Generated optimized machine learning-powered model, in light of the above two outcomes, for automated depth-resolved interpretation of tissue composition from PT-OCT images.
4- Increased the imaging rate of PT-OCT by orders of magnitude by introducing a new variant of PT-OCT based on pulsed photothermal excitation.
5- Developed algorithms for signal denoising and improving the quality of received signals and the contrast in images which in return enables faster PT-OCT imaging
Intracardiac Ultrasound Guided Systems for Transcatheter Cardiac Interventions
Transcatheter cardiac interventions are characterized by their percutaneous nature, increased patient safety, and low hospitalization times. Transcatheter procedures involve two major stages: navigation towards the target site and the positioning of tools to deliver the therapy, during which the interventionalists face the challenge of visualizing the anatomy and the relative position of the tools such as a guidewire. Fluoroscopic and transesophageal ultrasound (TEE) imaging are the most used techniques in cardiac procedures; however, they possess the disadvantage of radiation exposure and suboptimal imaging. This work explores the potential of intracardiac ultrasound (ICE) within an image guidance system (IGS) to facilitate the two stages of cardiac interventions. First, a novel 2.5D side-firing, conical Foresight ICE probe (Conavi Medical Inc., Toronto) is characterized, calibrated, and tracked using an electromagnetic sensor. The results indicate an acceptable tracking accuracy within some limitations. Next, an IGS is developed for navigating the vessels without fluoroscopy. A forward-looking, tracked ICE probe is used to reconstruct the vessel on a phantom which mimics the ultrasound imaging of an animal vena cava. Deep learning methods are employed to segment the complex vessel geometry from ICE imaging for the first time. The ICE-reconstructed vessel showed a clinically acceptable range of accuracy. Finally, a guidance system was developed to facilitate the positioning of tools during a tricuspid valve repair. The designed system potentially facilitates the positioning of the TriClip at the coaptation gap by pre-mapping the corresponding site of regurgitation in 3D tracking space
Atherosclerosis: Methods and Protocols
This volume provides detailed, up-to-date methods used in research on Atherosclerosis. Chapters guide readers through an overview of the pathogenesis of atherosclerosis and model systems together with in vitro, ex vivo, in vivo and emerging methods in atherosclerosis research. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and tips on troubleshooting and avoiding known pitfalls.
Authoritative and cutting-edge, Atherosclerosis: Methods and Protocols serves as an invaluable resource for those engaging in research on atherosclerosis and cardiovascular disease, as well as for researchers who are new to t
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