Accurate insertion and monitoring of metal implants in-vivo is essential for clinical diagnosis and therapy of various diseases. Clinical studies and examples have demonstrated that the misplacement errors of these metal devices can have dramatic consequences. This thesis focuses on three main metal devices that are in widespread use today: needles, coronary stents and brachytherapy seeds. Each application requires proper image-guidance for correct usage. For needles, image guidance is required to ensure correct local injection delivery or needle aspiration biopsy. Fine needle aspiration biopsies are performed in order to avoid major surgical excisions when obtaining tissue biopsy procedures. However, because of the small biopsy sample, the risk is that the sample is collected outside of the tumorigenic region, resulting in a false negative result. Implantation of stents requires that confirmation that proper stent apposition has been achieved due to balloon inflation. Furthermore, it is important to guide the stent to shield the vulnerable region of an atherosclerotic plaque. With prostate brachytherapy seeds, the ability to monitor seed placement is crucial because needle deflections or tissue deformation can result in seed misplacement errors, decreasing the efficacy of the pre-established treatment plan. For the described applications and other possible clinical practices involving the use of metallic implants, an imaging technology that can accurately depict the location of the metal objects, relative to their respective backgrounds, in real-time, is necessary to improve the safety and the efficacy of these procedures. Currently, ultrasound is used because of its real-time capabilities, non-ionizing radiation, and soft tissue contrast. However, due to high acoustic scattering from tissue, the contrast of metal implants can be low. Photoacoustic imaging can be used as an alternative, or complementary, imaging method to ultrasound for imaging metal. This thesis focuses on the benefits and the pitfalls of using photoacoustic imaging for detecting three different metal implants, each having unique requirements. Overall, the goal of this work is to develop a framework for clinical applications using combined ultrasound and photoacoustic imaging to help guide, detect and follow-up on clinical metal implants introduced in-vivo. / text

A pose estimation method is proposed for measuring the position and orientation of a biopsy needle. The technique is to be used as a touchless needle guide system for guidance of percutaneous procedures with 4D ultrasound. A pair of uncalibrated, light-weight USB cameras are used as inputs. A database is prepared offline, using both the needle line estimated from camera-captured images and the true needle line recorded from an independent tracking device. A nonparametric learning algorithm determines the best fit model from the database. This model can then be used in real-time to estimate the true position of the needle with inputs from only the camera images. Simulation results confirm the feasibility of the method and show how a small, accurately made database can provide satisfactory results. In a series of tests with cameras, we achieved an average error of 2.4mm in position and 2.61° in orientation. The system is also extended to real ultrasound imaging, as the two miniature cameras capture images of the needle in air and the ultrasound system captures a volume as the needle moves through the workspace. A new database is created with the estimated 3D position of the needle from the ultrasound volume and the 2D position and orientation of the needle calculated from the camera images. This study achieved an average error of 0.94 mm in position and 3.93° in orientation.

Many opportunities exist in medical ultrasound research for experimenting with novel designs, both of transducers and of signal processing techniques. However any experiment must have a reliable platform on which to develop these techniques. In my thesis work, I have designed, built, and tested a high-speed reconfigurable ultrasound beamforming platform. The complete receive beamformer system described in this thesis consists of hardware, firmware, and software components. All of these components work together to provide a platform for beamforming that is expandable, high-speed, and robust. The complexity of the operations being performed is hidden from the user by a simple to use and accessible software interface. Existing beamformer hardware is usually designed for real-time 2D image formation often using serial processing. The platform I built uses parallel processing in order to process ultrasound images 100 times faster than conventional systems. Conventional hardware is locked to a single or small number of similar transducers, while my design can be on-the-fly reprogrammed to work with nearly any transducer type. The system is also expandable to handle any size of device, while conventional systems can only handle a fixed number of device channels. The software I have created interfaces with the hardware and firmware components to provide an easy way to make use of the system’s reconfigurability. It also delivers a platform that can be simply expanded to host post-processing or signal analysis software to further fulfill a researcher’s needs. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-12-10 11:23:01.961

This thesis presents the design of a high-frequency annular array ultrasound system suitable for medical imaging. To reduce the cost of the system, off-the-shelf parts were used whenever possible. The system consists of four main components; 1) a transmit beamformer, 2) a high voltage pulse generator, 3) an annular array transducer and 4) a receive beamformer. The transmit beamformer and pulser were designed for an 8-channel array but could be easily expanded for larger arrays. The pulser produces monocycle electrical pulses with centre frequencies that could be adjusted from 10-50 MHz and with amplitudes up to 90 Vpp. The annular array transducer has 12 equal area elements and a total active aperture of 6 mm. The transducer array produced pulses with a centre frequency of 20 MHz and 50% bandwidth. The resulting images had a lateral resolution of 172.5 μm at 10 mm and an axial resolution of 180 μm. A new fabrication method was developed that makes it easier to build the array. The receive beamformer was based on a commercial 8-channel analog-to-digital converter. The digital signals were transferred to a laptop where the beamforming was performed in software. This avoided the need to develop custom hardware and allowed it to be reconfigured for different transducers by simply modifying the software. The beamformer used a new interpolation method that reduced the required sampling frequency while maintaining a satisfactory radiation pattern. The system produces images at 10 frames/sec. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-05-06 13:15:34.495

A novel technique for blind deconvolution of ultrasound is introduced. Existing deconvolution techniques for ultrasound such as cepstrum-based methods and the work of Adam and Michailovich – based on Discrete Wavelet Transform (DWT) shrinkage of the log-spectrum – exploit the smoothness of the pulse log-spectrum relative to the reflectivity function to estimate the pulse. To reduce the effects of non-stationarity in the ultrasound signal on both the pulse estimation and deconvolution, the log-spectrum is time-localized and represented as the Continuous Wavelet Transform (CWT) log-scalogram in the proposed technique. The pulse CWT coefficients are estimated via DWT shrinkage of the log-scalogram and are then deconvolved by wavelet-domain Wiener filtering. Parameters of the technique are found by heuristic optimization on a training set with various quality metrics: entropy, autocorrelation 6-dB width and fractal dimension. The technique is further enhanced by using different CWT wavelets for estimation and deconvolution, similar to the WienerChop method.

Analysis of the waveforms obtained from the umbilical artery using Doppler ultrasound has been claimed in a number of recent reports to be a highly specific method of identifying babies with intrauterine growth retardation. Because of the morbidity and mortality associated with this condition it was important to evaluate the validity of those claims before introducing the method into obstetric practise. The work in this thesis was carried out in four parts. Firstly the technique was found to be reproducible with small intra and inter-observer errors. Secondly, possible influencing factors were studied, and it was found that the fetal heart rate and fetal breathing movements have a significant effect on the waveform. Thirdly, a longitudinal study of 50 healthy women with normal pregnancies was performed to define the normal range of A/B ratios (the principle method of analysis of the waveforms was the A/B ratio: ratio of peak systolic to end-diastolic frequency). Finally, Doppler ultrasound was performed in 205 women with high risk pregnancies, and results were compared to the normal reference data. When high risk cases with abnormal Doppler results (A/B ratio > 95th centile) were compared with high risk cases with normal Doppler results (A/B ratio < 95th centile) the Doppler abnormal group were found to have a significantly increased incidence of preterm delivery, operative delivery, late fetal heart rate decelerations in labour, increased admission to the special care baby unit, and increased neonatal morbidity. Although an abnormal Doppler result was associated with small for gestational age in 61% of cases, only 41% of cases of small for gestational age had abnormal Doppler results. The conclusion from this thesis is that Doppler flow velocity waveform analysis, although lacking the previously claimed diagnostic precision of detecting intrauterine growth retardation, could contribute to fetal management by identifying babies at high risk of intrapartum complications.

The effects of ultrasound on the cell membrane of HeLa cells have been investigated using 750 KHz and 1.5 MHz transducers. The insonation chamber was designed to present minimum perturbance to ultrasound, while a castor-oil filled cylinder was used to reduce unwanted reflections and subsequent interference. Cells were insonated in monolayers and cell suspensions using continuous wave ultrasound with peak intensities up to 7 W/cm² for both transducers and temperatures up to 45^oC. The insonations were carried out in progressive wave and standing wave fields. Scanning Electron Microscopy revealed damage to cell membrane of cells insonated in suspension in the standing wave fields. No damage was inflicted on HeLa cells in the monolayers which were insonated under otherwise identical conditions. Furthermore, the damage was absent in both the cell suspensions and monolayers when insonated in the progressive wave fields. The observed damage progressed through distinct stages and it was temperature and intensity dependent. Cavitation monitoring indicated the presence of oscillating gas bubbles rather than collapse cavitation. In general, all these findings have given support to shearing stresses as the likely mechanism responsible for the damage. The severity of damage produced in the HeLa cell membrane strengthens the view held by other workers that the cell membrane is a major target for ultrasound damage. Coulter Counter study has also demonstrated the dependence of cell damage on the geometry of the container and highlights the importance of specifying the precise insonation conditions. ESR spin labelling technique has been employed in this study to probe the ultrasound effect on the fluidity of cell membrane. This preliminary investigation indicated that ultrasound increases the fluidity of the cell membrane. The implication of this increase in fluidity has been discussed.

This thesis is in the area of ultrasound tomography, which is a non-destructive imaging method that attempts to create quantitative images of the acoustical properties of an object of interest (OI). Specifically, three quantitative images per OI are created in this thesis, two of which correspond to the complex compressibility profile of the OI, and the other corresponds to its density profile. The focus of this thesis is on the development of an appropriate two-dimensional inverse scattering algorithm to create these quantitative images. The core of this algorithm is the Born iterative method that is used in conjunction with a fast and efficient method of moments forward solver, a Krylov subspace regularization technique, and a balancing method. This inversion algorithm is capable of simultaneous inversion of multiple-frequency data, and can handle a large imaging domain. This algorithm is finally tested against synthetic and measured data.

A novel technique for blind deconvolution of ultrasound is introduced. Existing deconvolution techniques for ultrasound such as cepstrum-based methods and the work of Adam and Michailovich – based on Discrete Wavelet Transform (DWT) shrinkage of the log-spectrum – exploit the smoothness of the pulse log-spectrum relative to the reflectivity function to estimate the pulse. To reduce the effects of non-stationarity in the ultrasound signal on both the pulse estimation and deconvolution, the log-spectrum is time-localized and represented as the Continuous Wavelet Transform (CWT) log-scalogram in the proposed technique. The pulse CWT coefficients are estimated via DWT shrinkage of the log-scalogram and are then deconvolved by wavelet-domain Wiener filtering. Parameters of the technique are found by heuristic optimization on a training set with various quality metrics: entropy, autocorrelation 6-dB width and fractal dimension. The technique is further enhanced by using different CWT wavelets for estimation and deconvolution, similar to the WienerChop method.

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