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The Design, Fabrication and Characterization of Capacitive Micromachined Ultrasonic Transducers for Imaging ApplicationsLogan, Andrew Stephan 29 September 2010 (has links)
Capacitive micromachined ultrasonic transducers (CMUTs) have proven themselves to be excellent candidates for medical ultrasonic imaging applications. The use of semiconductor fabrication techniques facilitates the fabrication of high quality arrays of uniform cells and elements, broad acoustic bandwidth, the potential to integrate the transducers with the necessary electronics, and the opportunity to exploit the benefits of batch fabrication.
In this thesis, the design, fabrication and testing of one- and two-dimensional CMUT arrays using a novel wafer bonding process whereby the membrane and the insulation layer are both silicon nitride is reported. A user-grown insulating membrane layer avoids the need for expensive SOI wafers, permits optimization of the electrode size, and allows more freedom in selecting the membrane thickness, while also enjoying the benefits of wafer bonding fabrication. Using a row-column addressing scheme for an NxN two-dimensional array permits three-dimensional imaging with a large reduction in the complexity of the array when compared to a conventional 2D array with connections to all N2 elements. Only 2N connections are required and the image acquisition rate has the potential to be greatly increased. A simplification of the device at the imaging end will facilitate the integration of a three-dimensional imaging CMUT array into either an endoscope or catheter which is the ultimate purpose of this research project.
To date, many sizes of transducers which operate at different frequencies have been successfully fabricated. Initial characterization in terms of resonant frequency and, transmission and reception in immersion has been performed on most of the device types. Extensive characterization has been performed with a linear 32 element array transducer and a 32x32 element row-column transducer. Two- and three-dimensional phased array imaging has been demonstrated.
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Characterization of Perfluorocarbon Droplets for Focused Ultrasound TherapySchad, Kelly C. 15 February 2010 (has links)
Focused ultrasound therapy can be enhanced with microbubbles by thermal and cavitation effects. However, localization of treatment becomes difficult as bioeffects can occur outside of the target region. Spatial control of gas bubbles can be achieved with
acoustic vaporization of perfluorocarbon droplets. This study was undertaken to determine the acoustic parameters for bubble production by droplet vaporization and how it
depends on the acoustic conditions and droplet physical parameters. Droplets of varying sizes were sonicated in vitro with a focused ultrasound transducer and varying frequency and exposure. Simultaneous measurements of the vaporization and inertial cavitation thresholds were performed. The results show that droplets cannot be vaporized at low frequency without inertial cavitation occurring. However, the vaporization threshold decreased with increasing frequency, exposure and droplet size. In summary, we have demonstrated that droplet vaporization is feasible for clinically-relevant sized droplets and acoustic exposures.
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A New paradigm for Ultrasound-Based Tissue Typing in Prostate CancerMoradi, Mehdi 27 September 2008 (has links)
Prostate cancer is the most common malignancy among men. The gold
standard clinical diagnosis method for prostate cancer is histopathologic analysis of biopsy samples acquired under ultrasound
guidance. However, most prostate tumors lack visually distinct appearances on medical images. Therefore, pathologically significant
cases of cancer can be missed during biopsy, resulting in false negative or repeated trials. The goal of our research is to augment ultrasound-guided prostate biopsy by adding tissue typing information that can be used for targeted biopsies. As a new
paradigm in tissue typing, we hypothesize and demonstrate that if a specific location in tissue undergoes sequential interactions with ultrasound, the time series of echoes, which we call radiofrequency (RF) time series, would carry ``tissue typing'' information. We provide a potential physical explanation for this phenomenon and
justify it based on computer simulations of the ultrasound probe and scattering media. We also report laboratory and animal studies that illustrate the utility of the method. We rely on a set of seven spectral and fractal features extracted from RF time series for tissue typing.
To show the clinical value of the proposed approach, we report an ex-vivo study involving 35 patients in which the utility of
RF time series features for detection of prostate tumors is confirmed. The outcomes are validated using histopathologic disease
distribution maps provided for the studied specimen. We show that the RF time series features are powerful tissue typing parameters that result in an area under receiver operating characteristic (ROC)
curve of 0.87 in 10-fold cross validation for diagnosis of prostate cancer. They are significantly more accurate and sensitive than spectral features extracted from single RF frames, and also B-scan texture features (area under ROC curve of 0.78 and 0.72,
respectively). A combination of these three categories of features results in a feature vector that provides an area under ROC curve of 0.95 in 10-fold cross-validation and 0.82 in leave-one-patient-out cross validation for diagnosis of prostate cancer. Using this hybrid feature vector and support vector machines, we create cancer distribution probability maps that highlight areas of tissue with high risk of cancer. / Thesis (Ph.D, Computing) -- Queen's University, 2008-09-27 07:51:11.45
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Improvement of Speckle-Tracked Freehand 3-D Ultrasound Through the Use of Sensor FusionLang, Andrew 20 October 2009 (has links)
Freehand 3-D ultrasound (US) using a 2-D US probe has the advantage over conventional 3-D probes of being able to collect arbitrary 3-D volumes at a lower cost. Traditionally, generating a volume requires external tracking to record the US probe position. An alternative means of tracking the US probe position is through speckle tracking. Ultrasound imaging has the advantage that the speckle inherent in all images contains relative position information due to the decorrelation of speckle over distance. However, tracking the position of US images using speckle information alone suffers from drifts caused by tissue inconsistencies and overall lack of accuracy.
This thesis presents two novel methods of improving the accuracy of speckle-tracked 3-D US through the use of sensor fusion. The first method fuses the speckle-tracked US positions with those measured by an electromagnetic (EM) tracker. Measurements are combined using an unscented Kalman filter (UKF). The fusion is able to reduce drift errors as well as to eliminate high-frequency jitter noise from the EM tracker positions. Such fusion produces a smooth and accurate 3-D reconstruction superior to those using the EM tracker alone.
The second method involves the registration of speckle-tracked 3-D US volumes to preoperative CT volumes. We regard registration combined with speckle tracking as a form of sensor fusion. In this case, speckle tracking is used in the registration to generate an initial position for each US image. To improve the accuracy of the US-to-CT registration, the US volume is registered to the CT volume by creating individual US "sub-volumes", each consisting of a small section of the entire US volume. The registration proceeds from the beginning of the US volume to the end, registering every sub-volume. The work is validated through spine phantoms created from clinical patient CT data as well as an animal study using a lamb cadaver. Using this technique, we are able to successfully register a speckle-tracked US volume to a CT volume with excellent accuracy. As a by-product of accurate registration, any drift from the speckle tracking is eliminated and the freehand 3-D US volume is improved. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2009-10-19 00:10:25.717
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Characterization of Ultrasound Elevation Beamwidth Artefacts for Brachytherapy Needle InsertionPEIKARI, MOHAMMAD 01 September 2011 (has links)
Ultrasound elevation beamwidth is the out of plane thickness causing image artefacts
normally appearing around anechoic areas in the medium. These artefacts could also
cause uncertainties in localizing objects (such as a surgical needle) in the ultrasound
image slices. This thesis studies the clinical significance of elevation beamwidth artefacts
in needle insertion procedures. A new measurement device was constructed to
measure the transrectal ultrasound elevation beamwidth. The beam profiles of various
lateral and axial distances to the transducer were generated. It is shown that
the ultrasound elevation beamwidth converges to a point within its focal zone close
to the transducer. This means that the transrectal ultrasound images have the best
resolution within the focal zone of the ultrasound close to the transducer. It is also
shown that the ultrasound device settings have a considerable impact on the amount
of beamwidth artefacts. Needle tip localization error was examined for a curvilinear
transrectal ultrasound transducer. Beveled prostate brachytherapy needles were inserted
through all holes of a grid template orthogonal to the axial beam axis. The
effects of device imaging parameters were also investigated on the amount of localization
error. Based on the developed results, it was found that the imaging parameters
of an ultrasound device have direct impact on the amount of object localization error
from 0.5 mm to 4 mm. The smallest localization error occurs laterally close to the center of the grid template, and axially within the beam’s focal zone. Similarly, the
largest localization error occurs laterally around both sides of the grid template, and
axially within the beam’s far field. Using the ultrasound device with appropriate
imaging settings could minimize the effects of these artefacts. We suggest to reduce
the gain setting of the ultrasound device. This will reduce the energies assigned to
the off-axis beams and as a result, the elevation beamwidth artefacts are minimized. / Thesis (Master, Computing) -- Queen's University, 2011-09-01 15:27:43.098
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Application of Ultrasound to Guide Pedicle Screw Insertion during Scoliosis Surgery: a Feasibility StudyZhang, Chan Unknown Date
No description available.
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Attachment mechanisms of a novel, targeted, lipid-based, ultrasound contrast agentEdgeworth, Adele January 2010 (has links)
This thesis presents the development of a novel, targeted, lipid-based, microbubble ultrasound contrast agent (UCA) for assessment of coronary heart disease (CHD) with high frequency intravascular ultrasound (IVUS). The targeting mechanisms assessed for microbubble attachment include a streptavidin-biotin mechanism, electrostatic mechanism and antibody targeting. The microbubble has been optimized for use with 40MHz IVUS through an investigation into the effect of various production methods on the echogenicity of the agent. Echogenicity has been assessed from quantification of the RF data and determination of the mean ultrasound backscatter. Agitation was found to be the optimal method of production resulting in a 3.94(±1.14)dB increase in the mean backscatter. The stability of the agent has also been assessed over time and optimal storage of the agent determined. A novel flow chamber has been developed for assessment of microbubble detachment under very high WSS. The flow chamber has been calibrated to 50Pa wall shear stress (WSS) using laser Doppler anemometry (LDA). Higher WSS was achieved through the use of higher viscosity fluids. The streptavidin-biotin bond has been assessed within the flow chamber and was found to be 75 times stronger than an electrostatic control. Antibody attachment to the microbubbles via a streptavidin-biotin bridge has been optimised with 91.20(±0.02)% of the microbubbles having antibodies attached. A flow system has also been developed for assessment of microbubble attachment to cells under very low WSS. Microbubbles have been successfully targeted to SK-Hep-1 cells using acoustic radiation force. In addition attachment of the microbubbles to SK-Hep-1 cells has been observed under 0.03Pa WSS in the Ibidi μ-slides.
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Ultrasound imaging in the diagnosis of muscle diseaseHeckmatt, J. Z. January 1984 (has links)
No description available.
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Decreasing Error in Functional Hip Joint Center Calculation using Ultrasound ImagingUpadhyaya, Swati 16 September 2013 (has links)
The hip joint center (HJC) is needed for calculation of hip kinematics in various applications. In the functional method, the center is determined by moving femur with respect to acetabulum. A popular way for measuring this movement is through an optical motion capture system. This method is fast and economical for most applications where we require an instant HJC even though the reconstruction error in bone position calculation exists due to skin artifact. This error is caused by movement of markers placed on skin rather than on actual bone. Here we introduce ultrasound imaging as an additional modality to measure the change in soft tissue thickness above bone while hip is flexed. We use this information on the tissue thickness change to recalculate position of markers placed on skin to match the movement of bone. A good advantage of using ultrasound machine is its non-invasiveness. We calculated HJC using a symmetric center of rotation estimation (SCoRE) algorithm, which uses the concept of coordinate transformation on 3D marker position data. The algorithm gives the 3D position of two centers, one for each hip bone. The distance between these two centers (SCoRE residual) gives us a hint on the accuracy of the HJC calculation and has been proved to be proportional to the error with respect to actual center in previous studies. These two centers should ideally coincide as they collectively form a spherical joint. Our new algorithm for HJC calculation with tissue thickness compensation, measured using ultrasound imaging shows the error has been reduced from 9.13 mm to 4.87 mm
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Evaluation of hybrid GSC-based and ASSB-based beamforming methods applied to ultrasound imagingAlbulayli, Mohammed Bani M. 09 August 2012 (has links)
The application of adaptive beamforming to biomedical ultrasound imaging has been an active research area in recent years. Adaptive beamforming techniques have the capability of achieving excellent resolution and sidelobe suppression, thus improving the quality of the ultrasound images. This quality improvement, however, comes at a high computational cost. The work presented in this thesis aims to answer the following basic question: Can we reduce the computational complexity of adaptive beamforming without a significant degradation of the image quality? Our objective is to explore a combination of low-complexity non-adaptive beamforming, such as the conventional Delay-and-Sum (DAS) method, with high-complexity adaptive beamforming, such as the standard Minimum-Variance Distortionless Response (MVDR) method implemented using the Generalized Sidelobe Canceller (GSC). Such a combination should have the lower computational complexity than adaptive beamforming, but it should also offer the image quality comparable to that obtained using adaptive beamforming. In addition to the adaptive GSC-based MVDR beamforming method, we also investigate the performance of the so-called Adaptive Single Snapshot Beamformer (ASSB), which is relatively unexplored in the ultrasound imaging literature.
The main idea behind our approach to combining a non-adaptive beamformer with an adaptive one is based on the use of the data-dependent variable known as the coherence factor. The resulting hybrid beamforming method can be summarized as follows: For each input snapshot to be beamformed, calculate the corresponding coherence factor; if the coherence factor is below a certain threshold, use non-adaptive DAS beamforming, otherwise use adaptive (GSC-based or ASSB-based) beamforming. We have applied this simple switching scheme to the simulated B-mode ultrasound images of the 12-point and point-scatterer-cyst phantoms that are commonly used in the ultrasound imaging literature to evaluate the image quality. Our simulation results show that, in comparison to optimal high-complexity always-adaptive beamforming, our hybrid beamformer can yield significant computational savings that range from 59% to 99%, while maintaining the image quality (measured in terms of resolution and contrast) within a 5% degradation margin. / Graduate
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