This thesis describes the experimental procedure and results of an investigation into the effect of electric and acoustic fields on dead end vacuum filtration. The test suspension used was low concentration titanium dioxide. Ultrasound energy was applied tangentially and electrical energy parallel to the filter medium. Varying electric field gradients were applied to the filter cell, either alone or together with the constant frequency acoustic field. The filter cell was based on a Nutsche filter, and allowed samples of cake to be taken at the end of the filtration experiment. Electric and acoustic field strengths, suspension characteristics and process parameters could all be varied independently.

The increasing use of Point of Care (POC) ultrasound presents a challenge in providing efficient training to new POC ultrasound users. In response to this need, we have developed an affordable, compact, laptop-based obstetric ultrasound training simulator. It offers freehand ultrasound scan on an abdomen-sized scan surface with a 5 degrees of freedom sham transducer and utilizes 3D ultrasound image volumes as training material. On the simulator user interface is rendered a virtual torso, whose body surface models the abdomen of a particular pregnant scan subject. A virtual transducer scans the virtual torso, by following the sham transducer movements on the scan surface. The obstetric ultrasound training is self-paced and guided by the simulator using a set of tasks, which are focused on three broad areas, referred to as modules: 1) medical ultrasound basics, 2) orientation to obstetric space, and 3) fetal biometry. A learner completes the scan training through the following three steps: (i) watching demonstration videos, (ii) practicing scan skills by sequentially completing the tasks in Modules 2 and 3, with scan evaluation feedback and help functions available, and (iii) a final scan exercise on new image volumes for assessing the acquired competency. After each training task has been completed, the simulator evaluates whether the task has been carried out correctly or not, by comparing anatomical landmarks identified and/or measured by the learner to reference landmark bounds created by algorithms, or pre-inserted by experienced sonographers. Based on the simulator, an ultrasound E-training system has been developed for the medical practitioners for whom ultrasound training is not accessible at local level. The system, composed of a dedicated server and multiple networked simulators, provides synchronous and asynchronous training modes, and is able to operate with a very low bit rate. The synchronous (or group-learning) mode allows all training participants to observe the same 2D image in real-time, such as a demonstration by an instructor or scan ability of a chosen learner. The synchronization of 2D images on the different simulators is achieved by directly transmitting the position and orientation of the sham transducer, rather than the ultrasound image, and results in a system performance independent of network bandwidth. The asynchronous (or self-learning) mode is described in the previous paragraph. However, the E-training system allows all training participants to stay networked to communicate with each other via text channel. To verify the simulator performance and training efficacy, we conducted several performance experiments and clinical evaluations. The performance experiment results indicated that the simulator was able to generate greater than 30 2D ultrasound images per second with acceptable image quality on medium-priced computers. In our initial experiment investigating the simulator training capability and feasibility, three experienced sonographers individually scanned two image volumes on the simulator. They agreed that the simulated images and the scan experience were adequately realistic for ultrasound training; the training procedure followed standard obstetric ultrasound protocol. They further noted that the simulator had the potential for becoming a good supplemental training tool for medical students and resident doctors. A clinic study investigating the simulator training efficacy was integrated into the clerkship program of the Department of Obstetrics and Gynecology, University of Massachusetts Memorial Medical Center. A total of 24 3rd year medical students were recruited and each of them was directed to scan six image volumes on the simulator in two 2.5-hour sessions. The study results showed that the successful scan times for the training tasks significantly decreased as the training progressed. A post-training survey answered by the students found that they considered the simulator-based training useful and suitable for medical students and resident doctors. The experiment to validate the performance of the E-training system showed that the average transmission bit rate was approximately 3-4 kB/s; the data loss was less than 1% and no loss of 2D images was visually detected. The results also showed that the 2D images on all networked simulators could be considered to be synchronous even though inter-continental communication existed.

"Ultrasound imaging is a safe and powerful tool for providing detailed still and moving images of the human body. Most of today’s ultrasound systems are housed on a movable cart and designed for use within a clinical setting, such as in a hospital or doctor’s office. This configuration hinders its use in locations lacking controlled environments and stable power sources. Example locations include ambulances, disaster sights, war zones and rural medicine. A wearable ultrasound system, in the form of a vest worn by a sonographer, has been developed as a complete solution for performing untethered ultrasound examinations. The heart of the system is an enclosure containing an embedded computer running the Windows XP operating system, and a custom power supply. The power supply integrates a battery charger, a switching regulator, two linear regulators, a variable speed fan controller and a microcontroller providing an interface for monitoring and control to the embedded computer. Operation of the system is generally accomplished through the use of voice commands, but it may also be operated using a hand-held mouse. It is capable of operating for a full day, using two batteries contained in the vest. In addition, the system has the capability to wirelessly share live images with remote viewers in real-time, while also permitting full duplex voice communication. An integrated web-server also provides for the wireless retrieval of stored images, image loops and other information using a web-browser. "

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Medical ultrasound imaging is widely used to diagnose cardiacdiseases. The recent availability of real time 3D ultrasound posesseveral interesting challenges and opportunities, and the work of thisthesis is devoted to both challenges and opportunities. One of the key benefits of ultrasound imaging is that its images arereal time. This has been challenged with the recent introduction of 3Dimages, where the number of ultrasound beams is squared compared totraditional 2D images. One common way to alleviate this is byreceiving several closely spaced ultrasound beams from each pulsetransmission, which increases acquisition speed but affects the imagequality. Specifically, B-mode images are irregularly sampled and losespatial shift invariance while a bias in the Doppler velocityestimates causes a discontinuity in the velocity estimates in colorflow images. We have found that these artifacts can be reducedsignificantly by interpolation of the beamformed data from overlappingbeams, with the limitation of requiring at least twice the number ofbeamformers. We have also found that valvular regurgitation is one of thecardiac diseases that can benefit greatly from quantification ofseverity using 3D ultrasound. We have devised a modality that useshigh pulse repetition frequency 3D Doppler to isolate thebackscattered signal power from the vena contracta of a regurgitantjet. This measure is calibrated with a narrow reference beam insidethe jet to estimate the cross-sectional area of the vena contracta. Wehave validated this method with computer simulations, with an in vitrostudy and finally in vivo with 27 patients who had mitralregurgitation. We found that the cross-sectional area and regurgitantvolume of the vena contracta could be quantified without bias as long as the orifice was sufficiently large for a calibration beam tofit inside it. The severity of smaller regurgitations will beoverestimated, but this does not pose a clinical problem, as thesepatients can easily be identified by standard 2D Doppler examination and donot typically need further quantification. Finally, we have developed a new, fast 3D ultrasound simulation methodthat can incorporate anisotropic scattering from cardiac muscle cells. This approach is three orders of magnitudefaster than the most commonly used simulation methods, making it wellsuited for the simulation of dynamic 3D images for development and testingof quantitative diagnostic methods such as 3D speckle tracking andvolumetric measurements.

In this thesis focused ultrasound thrombolysis was investigated in vitro and in vivo. At high intensities it was demonstrated that clot breakdown only arises under the presence of inertial cavitation for longer pulse lengths, consistent with observations at significantly shorter pulse durations, and that the majority of clot debris is sub-capillary in size. Evidence of flow restoration was demonstrated in vivo by partially restoring flow to an occluded rabbit femoral artery. At slightly lower intensities it was observed that steady- state clot displacements scale linearly with power for clots treated with focused ultrasound pulses, and in some cases can reach magnitudes up to several hundred microns. It was demonstrated that the shear strain exerted on the clot by a focused ultrasound pulse scale with power, which may be implicated in enhancing drug permeation for studies in combination with lytic agents.

In this thesis focused ultrasound thrombolysis was investigated in vitro and in vivo. At high intensities it was demonstrated that clot breakdown only arises under the presence of inertial cavitation for longer pulse lengths, consistent with observations at significantly shorter pulse durations, and that the majority of clot debris is sub-capillary in size. Evidence of flow restoration was demonstrated in vivo by partially restoring flow to an occluded rabbit femoral artery. At slightly lower intensities it was observed that steady- state clot displacements scale linearly with power for clots treated with focused ultrasound pulses, and in some cases can reach magnitudes up to several hundred microns. It was demonstrated that the shear strain exerted on the clot by a focused ultrasound pulse scale with power, which may be implicated in enhancing drug permeation for studies in combination with lytic agents.

The intensities associated with the propagation of diagnostic and therapeutic ultrasound pulses are large enough to require a nonlinear description. As a nonlinear wave propagates it distorts, creating harmonics and eventually acoustic shocks. Harmonics can be used to generate images with improved spatial resolution and less clutter. The energy from nonlinear waves is deposited in a different way than in the linear case which modifies predictions for in situ acoustic exposure. Tissue heating and radiation force depend on this intensity. High intensity shock waves are essential for stone communition with lithotripsy because it depends on the shear gradients caused by the pressure differentials and on the peak negative pressures for cavitation. The work presented in this dissertation investigates numerical simulations that solve nonlinear ultrasonic wave propagation in both the strongly nonlinear regime, where shocks develop, and the weakly nonlinear regime, where the acoustic attenuation prevents the formation of pressure discontinuities. The Rankine-Hugoniot relation for shock wave propagation describes the shock speed of a nonlinear wave. This dissertation investigates time domain numerical methods that solve the nonlinear parabolic wave equation, or the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, and the conditions they require to satisfy the Rankine-Hugoniot relation. Two numerical methods commonly used in hyperbolic conservation laws are adapted to solve the KZK equation: Godunov's method and the monotonic upwind scheme for conservation laws (MUSCL). It is shown that they satisfy the Rankine-Hugoniot relation regardless of attenuation. These two methods are compared with the current implicit solution based method. When the attenuation is small, such as in water, the current method requires a degree of grid refinement that is computationally impractical. All three numerical methods are compared in simulations for lithotripters and high intensity focused ultrasound (HIFU) where the attenuation is small compared to the nonlinearity because much of the propagation occurs in water. The simulations are performed on grid sizes that are consistent with present-day computational resources but are not sufficiently refined for the current method to satisfy the Rankine-Hugoniot condition. It is shown that satisfying the Rankine-Hugoniot conditions has a significant impact on metrics relevant to lithotripsy (such as peak pressures), and HIFU (intensity). Because the Godunov and MUSCL schemes satisfy the Rankine-Hugoniot conditions on coarse grids they are particularly advantageous for three dimensional simulations. The propagation of focused and intense ultrasound beams is determined by nonlinearity, diffraction, and absorption. Most descriptions of nonlinear wave propagation in ultrasound, such as the KZK equation, rely on quadratic nonlinearity. At diagnostic and some therapeutic amplitudes the quadratic, or B/A, term dominates the nonlinear term. However, when the amplitudes are sufficiently large, such as in shock wave lithotripsy, the cubic, or C/A, term becomes significant. Conventionally the parabolic wave equation has only included the quadratic terms. This dissertation establishes a time domain numerical method that solves the parabolic wave equation with cubic nonlinearity in an attenuating medium. The differences between solutions of the quadratic and cubic equations for a focused lithotripter in a water bath are investigated. A study of numerical solutions to the linear full-wave equation and the KZK or parabolic wave equation is presented. Finite difference time domain methods are used to calculate the acoustic field emitted from a diagnostic ultrasound transducer. Results are compared to Field II, a simulation package that has been used extensively to linearly model transducers in ultrasound. The simulation of the parabolic equation can accurately predict the lateral beamplot for large F-numbers but exhibits errors for small F-numbers. It also overestimates the depth at which the focus occurs. It is shown that the finite difference solution of the full-wave equation is accurate for small and large F-numbers. The lateral beamplots and axial intensities are in excellent agreement with the Field II simulations. For these reasons the KZK equation is abandoned in favor of the full-wave equation to describe nonlinear propagation for ultrasound imaging. A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). Three dimensional solutions of the equation are verified with water tank measurements of a commercial diagnostic ultrasound transducer and are shown to be in excellent agreement in terms of the fundamental and harmonic acoustic fields, and the power spectrum at the focus. The linear and nonlinear components of the algorithm are also verified independently. In the linear non-attenuating regime solutions match simulations from Field II to within 0.3 dB. Nonlinear plane wave propagation is shown to closely match results from the Galerkin method up to four times the fundamental frequency. In addition to thermoviscous attenuation we present a numerical solution of the relaxation attenuation laws that allows modeling of arbitrary frequency dependent attenuation, such as that observed in tissue. A perfectly matched layer (PML) is implemented at the boundaries with a novel numerical implementation that allows the PML to be used with high order discretizations. A -78 dB reduction in the reflected amplitude is demonstrated. The numerical algorithm is used to simulate a diagnostic ultrasound pulse propagating through a histologically measured representation of human abdominal wall with spatial variation in the speed of sound, attenuation, nonlinearity, and density. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beamforming algorithm to generate images. The resulting harmonic image exhibits characteristic improvement in lesion boundary definition and contrast when compared to the fundamental image. We demonstrate a mechanism of harmonic image quality improvement by showing that the harmonic point spread function is less sensitive to reverberation clutter. Numerical solutions of the nonlinear full-wave equation in a heterogeneous attenuating medium are used to simulate the propagation of diagnostic ultrasound pulses through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-and-sum beamforming is used to generate point spread functions (PSF) from a point target located at the focus. These PSFs reveal that, for the particular imaging system considered, the primary source of degradation in fundamental imaging is due to reverberation from near-field structures. Compared to the harmonic PSF the mean magnitude of the reverberation clutter in the fundamental PSF is 26 dB higher. An artificial medium with uniform velocity but unchanged impedance characteristics is used to show that for the fundamental PSF the primary source of degradation is phase aberration. Ultrasound images are created in silico and these beamformed images are compared to images obtained from convolution of the PSF with a scatterer field to demonstrate that a very large portion of the PSF must be used to accurately represent the clutter observed in conventional imaging. Conventional delay-and-sum beamforming is used to generate images of an anechoic lesion located beneath the abdominal layer for various transducer configurations. Point spread functions (PSF) and estimates of the contrast to noise ratio (CNR) are used to quantify and determine the sources of improvement between harmonic and fundamental imaging. Simulations indicate that reducing the pressure amplitude at the transducer surface has no discernible effect on image quality. It is shown that when the aperture is reduced there is an increase in the image degradation due to reverberation clutter in the fundamental and an increase in the effects of reverberation and phase aberration in the harmonic. A doubling of the transmit frequency shows that the harmonic lesion CNR becomes worse than the fundamental CNR due to increases in pulse lengthening and phase aberration. Acoustic Radiation Force Impulse (ARFI) imaging uses brief, high intensity, focused ultrasound pulses to generate a radiation force that displaces tissue. Nonlinear propagation of acoustic pulses transfers energy to higher frequencies where it is preferentially absorbed by tissue. The radiation force is proportional to the absorbed energy. This dissertation examines the effects of nonlinearity on the displacements induced by radiation force with various ultrasound transducer configurations. A three dimensional numerical method that simulates nonlinear acoustic propagation is used to calculate the intensity and absorption losses for typical ARFI pulses. It is demonstrated that nonlinearity has a relatively small effect on the intensity but increases estimates of the loss by up to a factor of 20. The intensity fields obtained from the acoustic simulations are used as an input to a finite element method (FEM) model of the mechanical tissue response to a radiation force excitation. These simulations show that including nonlinearity in the acoustic intensity significantly reduces predictions of the displacement without having a significant impact on the lateral and elevation resolution. / Dissertation

The first objective was to estimate total internal fat in beef cattle based on a technique that measures kidney fat (uKFd) using real-time ultrasound (RTU). Data were obtained from 109 cattle from four studies, and animals were scanned 7 d preslaughter for uKFd and ultrasound backfat thickness. At slaughter carcass kidney fat depth (cKFd), KPH weight, and total internal fat were measured. The second objective was to characterize residual feed intake (RFI) in finishing cattle fed high grain diets and to examine the relationships with growth, ultrasound, carcass, non-carcass, and tenderness traits in two studies involving Santa Gertrudis (n = 114) steers, and Angus bulls (n = 16) and heifers (n = 16). In both experiments, RFI was calculated as the difference between actual DMI and predicted DMI. Results for the first objective indicated that RTU can be used to estimate cKFd, KPH weight and total internal fat (IFAT). Prediction equations developed to predict IFAT had R2 that ranged from 0.65 to 0.97 (P < 0.05). Results for the second objective indicate that RFI was not correlated with ADG, but was positively correlated with DMI and feed conversion ratio. Carcass 12th-rib fat depth was positively correlated with RFI in Santa Gertudis steers, such that steers with low RFI were leaner than steers with high RFI. Residual feed intake was not correlated with carcass or non-carcass composition traits in Angus bulls and heifers. Marbling and tenderness traits were not associated with RFI. Results from these studies indicate that we are able to measure IFAT with RTU, and that beef cattle producers can utilize RFI to identify animals that are more efficient with minimal impacts on growth, carcass composition and tenderness.

The purpose of the current study is to contribute to the understanding of prenatal cerebellar pathology in autism. Reduction of Purkinje neurons is well reported in the cerebella of individual’s with autism. While there is evidence to suggest that this abnormality may be evident as early as prenatal development, no study to date has examined in the anataomical prenatal development of the cerebella in children later diagnosed with autism. The primary prediction being made is that a reduction of Purkinje neurons during prenatal development will present as reduced cerebellar size in the reports from mother’s prenatal ultrasound records. It is hypothesized that this reduction will be greater in children with an autism diagnosis compared to the records of children without an autism diagnosis. The secondary prediction will attempt to further support the link between aberrant cerebellar development and increased stereotyped behavior and repetitive interests. A retrospective analysis of prenatal ultrasound records and autism diagnostic information will test these hypotheses, predicting that records from children who have been diagnosed with an autism spectrum disorder will show reductions in transverse cerebellar diameter measurements when compared to TD peers, and that greater reductions will correlate with increased stereotypical and repetitive behaviors as measured by a standard diagnostic tool. / text